stb-imv/stb_image.c

/* stbi-0.95 - public domain JPEG/PNG reader - http://nothings.org/stb_image.c
                      when you control the images you're loading

   QUICK NOTES:
      Primarily of interest to game developers and other people who can
          avoid problematic images and only need the trivial interface

      JPEG baseline (no JPEG progressive, no oddball channel decimations)
      PNG non-interlaced
      BMP non-1bpp, non-RLE
      writes BMP,TGA (define STBI_NO_WRITE to remove code)
      decoded from memory or through stdio FILE (define STBI_NO_STDIO to remove code)
        
   TODO:
      stbi_info_*
      PSD loader
  
   history:
      0.95   during header scan, seek to markers in case of padding
      0.94   STBI_NO_STDIO to disable stdio usage; rename all #defines the same
      0.93   handle jpegtran output; verbose errors
      0.92   read 4,8,16,24,32-bit BMP files of several formats
      0.91   output 24-bit Windows 3.0 BMP files
      0.90   fix a few more warnings; bump version number to approach 1.0
      0.61   bugfixes due to Marc LeBlanc, Christopher Lloyd
      0.60   fix compiling as c++
      0.59   fix warnings: merge Dave Moore's -Wall fixes
      0.58   fix bug: zlib uncompressed mode len/nlen was wrong endian
      0.57   fix bug: jpg last huffman symbol before marker was >9 bits but less
                      than 16 available
      0.56   fix bug: zlib uncompressed mode len vs. nlen
      0.55   fix bug: restart_interval not initialized to 0
      0.54   allow NULL for 'int *comp'
      0.53   fix bug in png 3->4; speedup png decoding
      0.52   png handles req_comp=3,4 directly; minor cleanup; jpeg comments
      0.51   obey req_comp requests, 1-component jpegs return as 1-component,
             on 'test' only check type, not whether we support this variant
*/


////   begin header file  ////////////////////////////////////////////////////
//
// Limitations:
//    - no progressive/interlaced support (jpeg, png)
//    - 8-bit samples only (jpeg, png)
//    - not threadsafe
//    - channel subsampling of at most 2 in each dimension (jpeg)
//    - no delayed line count (jpeg) -- IJG doesn't support either
//
// Basic usage:
//    int x,y,n;
//    unsigned char *data = stbi_load(filename, &x, &y, &n, 0);
//    // ... process data if not NULL ... 
//    // ... x = width, y = height, n = # 8-bit components per pixel ...
//    // ... replace '0' with '1'..'4' to force that many components per pixel
//    stbi_image_free(data)
//
// Standard parameters:
//    int *x       -- outputs image width in pixels
//    int *y       -- outputs image height in pixels
//    int *comp    -- outputs # of image components in image file
//    int req_comp -- if non-zero, # of image components requested in result
//
// The return value from an image loader is an 'unsigned char *' which points
// to the pixel data. The pixel data consists of *y scanlines of *x pixels,
// with each pixel consisting of N interleaved 8-bit components; the first
// pixel pointed to is top-left-most in the image. There is no padding between
// image scanlines or between pixels, regardless of format. The number of
// components N is 'req_comp' if req_comp is non-zero, or *comp otherwise.
// If req_comp is non-zero, *comp has the number of components that _would_
// have been output otherwise. E.g. if you set req_comp to 4, you will always
// get RGBA output, but you can check *comp to easily see if it's opaque.
//
// An output image with N components has the following components interleaved
// in this order in each pixel:
//
//     N=#comp     components
//       1           grey
//       2           grey, alpha
//       3           red, green, blue
//       4           red, green, blue, alpha
//
// If image loading fails for any reason, the return value will be NULL,
// and *x, *y, *comp will be unchanged. The function stbi_failure_reason()
// can be queried for an extremely brief, end-user unfriendly explanation
// of why the load failed. Define STBI_NO_FAILURE_STRINGS to avoid
// compiling these strings at all, and STBI_FAILURE_USERMSG to get slightly
// more user-friendly ones.
//
// Paletted PNG and BMP images are automatically depalettized.

#ifndef STBI_NO_STDIO
#include <stdio.h>
#endif

enum
{
   STBI_default = 0, // only used for req_comp

   STBI_grey       = 1,
   STBI_grey_alpha = 2,
   STBI_rgb        = 3,
   STBI_rgb_alpha  = 4,
};

typedef unsigned char stbi_uc;

#ifdef __cplusplus
extern "C" {
#endif

// WRITING API

#ifndef STBI_NO_WRITE
// write a BMP/TGA file given tightly packed 'comp' channels (no padding, nor bmp-stride-padding)
// (you must include the appropriate extension in the filename).
// returns TRUE on success, FALSE if couldn't open file, error writing file
extern int      stbi_write_bmp       (char *filename,           int x, int y, int comp, void *data);
extern int      stbi_write_tga       (char *filename,           int x, int y, int comp, void *data);
#endif

// PRIMARY API - works on images of any type

// load image by filename, open file, or memory buffer
#ifndef STBI_NO_STDIO
extern stbi_uc *stbi_load            (char *filename,           int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_load_from_file  (FILE *f,                  int *x, int *y, int *comp, int req_comp);
#endif
extern stbi_uc *stbi_load_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp);
// for stbi_load_from_file, file pointer is left pointing immediately after image

// get a VERY brief reason for failure
extern char    *stbi_failure_reason  (void);

// free the loaded image -- this is just free()
extern void     stbi_image_free      (stbi_uc *retval_from_stbi_load);

// get image dimensions & components without fully decoding
extern int      stbi_info            (char *filename,           int *x, int *y, int *comp);
extern int      stbi_info_from_file  (char *filename,           int *x, int *y, int *comp);
extern int      stbi_info_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp);

// ZLIB client - used by PNG, available for other purposes

extern char *stbi_zlib_decode_malloc_guesssize(int initial_size, int *outlen);
extern char *stbi_zlib_decode_malloc(char *buffer, int len, int *outlen);
extern int   stbi_zlib_decode_buffer(char *obuffer, int olen, char *ibuffer, int ilen);


// TYPE-SPECIFIC ACCESS

// is it a jpeg?
extern int      stbi_jpeg_test_file       (FILE *f);
extern int      stbi_jpeg_test_memory     (stbi_uc *buffer, int len);

extern stbi_uc *stbi_jpeg_load            (char *filename,           int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_jpeg_load_from_file  (FILE *f,                  int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_jpeg_load_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp);
extern int      stbi_jpeg_info            (char *filename,           int *x, int *y, int *comp);
extern int      stbi_jpeg_info_from_file  (FILE *f,                  int *x, int *y, int *comp);
extern int      stbi_jpeg_info_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp);

extern int      stbi_jpeg_dc_only; // only decode DC component

// is it a png?
extern int      stbi_png_test_file        (FILE *f);
extern int      stbi_png_test_memory      (stbi_uc *buffer, int len);

extern stbi_uc *stbi_png_load             (char *filename,           int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_png_load_from_file   (FILE *f,                  int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_png_load_from_memory (stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp);
extern int      stbi_png_info             (char *filename,           int *x, int *y, int *comp);
extern int      stbi_png_info_from_file   (FILE *f,                  int *x, int *y, int *comp);
extern int      stbi_png_info_from_memory (stbi_uc *buffer, int len, int *x, int *y, int *comp);

// is it a bmp?
extern int      stbi_bmp_test_file        (FILE *f);
extern int      stbi_bmp_test_memory      (stbi_uc *buffer, int len);

extern stbi_uc *stbi_bmp_load             (char *filename,           int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_bmp_load_from_file   (FILE *f,                  int *x, int *y, int *comp, int req_comp);
extern stbi_uc *stbi_bmp_load_from_memory (stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp);

#ifdef __cplusplus
}
#endif

//
//
////   end header file   /////////////////////////////////////////////////////

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <assert.h>
#include <stdarg.h>

#ifndef _MSC_VER
#define __forceinline
#endif

// implementation:
typedef unsigned char uint8;
typedef unsigned short uint16;
typedef   signed short  int16;
typedef unsigned int   uint32;
typedef   signed int    int32;
typedef unsigned int   uint;

// should produce compiler error if size is wrong
typedef unsigned char validate_uint32[sizeof(uint32)==4];

//////////////////////////////////////////////////////////////////////////////
//
// Generic API that works on all image types
//

static char *failure_reason;

char *stbi_failure_reason(void)
{
   return failure_reason;
}

static int e(char *str)
{
   failure_reason = str;
   return 0;
}

#ifdef STBI_NO_FAILURE_STRINGS
   #define e(x,y)  0
#elif defined(STBI_FAILURE_USERMSG)
   #define e(x,y)  e(y)
#else
   #define e(x,y)  e(x)
#endif

#define ep(x,y)   (e(x,y),NULL)   

void stbi_image_free(unsigned char *retval_from_stbi_load)
{
   free(retval_from_stbi_load);
}

#ifndef STBI_NO_STDIO
unsigned char *stbi_load(char *filename, int *x, int *y, int *comp, int req_comp)
{
   FILE *f = fopen(filename, "rb");
   unsigned char *result;
   if (!f) return ep("can't fopen", "Unable to open file");
   result = stbi_load_from_file(f,x,y,comp,req_comp);
   fclose(f);
   return result;
}

unsigned char *stbi_load_from_file(FILE *f, int *x, int *y, int *comp, int req_comp)
{
   if (stbi_jpeg_test_file(f))
      return stbi_jpeg_load_from_file(f,x,y,comp,req_comp);
   if (stbi_png_test_file(f))
      return stbi_png_load_from_file(f,x,y,comp,req_comp);
   if (stbi_bmp_test_file(f))
      return stbi_bmp_load_from_file(f,x,y,comp,req_comp);
   return ep("unknown image type", "Image not of any known type, or corrupt");
}
#endif

unsigned char *stbi_load_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp)
{
   if (stbi_jpeg_test_memory(buffer,len))
      return stbi_jpeg_load_from_memory(buffer,len,x,y,comp,req_comp);
   if (stbi_png_test_memory(buffer,len))
      return stbi_png_load_from_memory(buffer,len,x,y,comp,req_comp);
   if (stbi_bmp_test_memory(buffer,len))
      return stbi_bmp_load_from_memory(buffer,len,x,y,comp,req_comp);
   return ep("unknown image type", "Image not of any known type, or corrupt");
}

// @TODO: get image dimensions & components without fully decoding
extern int      stbi_info            (char *filename,           int *x, int *y, int *comp);
extern int      stbi_info_from_file  (char *filename,           int *x, int *y, int *comp);
extern int      stbi_info_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp);

//////////////////////////////////////////////////////////////////////////////
//
// Common code used by all image loaders
//

// image width, height, # components
static uint32 img_x, img_y;
static int img_n, img_out_n;

enum
{
   SCAN_load=0,
   SCAN_type,
   SCAN_header,
};

// An API for reading either from memory or file.
// It fits on a single screen. No abstract base classes needed.
#ifndef STBI_NO_STDIO
static FILE  *img_file;
#endif
static uint8 *img_buffer, *img_buffer_end;

#ifndef STBI_NO_STDIO
static void start_file(FILE *f)
{
   img_file = f;
}
#endif

static void start_mem(uint8 *buffer, int len)
{
#ifndef STBI_NO_STDIO
   img_file = NULL;
#endif
   img_buffer = buffer;
   img_buffer_end = buffer+len;
}

static int get8(void)
{
#ifndef STBI_NO_STDIO
   if (img_file) {
      int c = fgetc(img_file);
      return c == EOF ? 0 : c;
   }
#endif
   if (img_buffer < img_buffer_end)
      return *img_buffer++;
   return 0;
}

static int at_eof(void)
{
#ifndef STBI_NO_STDIO
   if (img_file)
      return feof(img_file);
#endif
   return img_buffer >= img_buffer_end;   
}

static uint8 get8u(void)
{
   return (uint8) get8();
}

static void skip(int n)
{
#ifndef STBI_NO_STDIO
   if (img_file)
      fseek(img_file, n, SEEK_CUR);
   else
#endif
      img_buffer += n;
}

static int get16(void)
{
   int z = get8();
   return (z << 8) + get8();
}

static uint32 get32(void)
{
   uint32 z = get16();
   return (z << 16) + get16();
}

static int get16le(void)
{
   int z = get8();
   return z + (get8() << 8);
}

static uint32 get32le(void)
{
   uint32 z = get16le();
   return z + (get16le() << 16);
}

static void getn(stbi_uc *buffer, int n)
{
#ifndef STBI_NO_STDIO
   if (img_file) {
      fread(buffer, 1, n, img_file);
      return;
   }
#endif
   memcpy(buffer, img_buffer, n);
   img_buffer += n;
}

//////////////////////////////////////////////////////////////////////////////
//
//  generic converter from built-in img_n to req_comp
//    individual types do this automatically as much as possible (e.g. jpeg
//    does all cases internally since it needs to colorspace convert anyway,
//    and it never has alpha, so very few cases ). png can automatically
//    interleave an alpha=255 channel, but falls back to this for other cases
//
//  assume data buffer is malloced, so malloc a new one and free that one
//  only failure mode is malloc failing

static uint8 compute_y(int r, int g, int b)
{
   return (uint8) (((r*77) + (g*150) +  (29*b)) >> 8);
}

static unsigned char *convert_format(unsigned char *data, int img_n, int req_comp)
{
   uint i,j;
   unsigned char *good;

   if (req_comp == img_n) return data;
   assert(req_comp >= 1 && req_comp <= 4);

   good = (unsigned char *) malloc(req_comp * img_x * img_y);
   if (good == NULL) {
      free(data);
      return ep("outofmem", "Out of memory");
   }

   for (j=0; j < img_y; ++j) {
      unsigned char *src  = data + j * img_x * img_n   ;
      unsigned char *dest = good + j * img_x * req_comp;

      #define COMBO(a,b)  ((a)*8+(b))
      #define CASE(a,b)   case COMBO(a,b): for(i=0; i < img_x; ++i, src += a, dest += b)

      // convert source image with img_n components to one with req_comp components
      switch(COMBO(img_n, req_comp)) {
         CASE(1,2) dest[0]=src[0], dest[1]=255; break;
         CASE(1,3) dest[0]=dest[1]=dest[2]=src[0]; break;
         CASE(1,4) dest[0]=dest[1]=dest[2]=src[0], dest[3]=255; break;
         CASE(2,1) dest[0]=src[0]; break;
         CASE(2,3) dest[0]=dest[1]=dest[2]=src[0]; break;
         CASE(2,4) dest[0]=dest[1]=dest[2]=src[0], dest[3]=src[1]; break;
         CASE(3,4) dest[0]=src[0],dest[1]=src[1],dest[2]=src[2],dest[3]=255; break;
         CASE(3,1) dest[0]=compute_y(src[0],src[1],src[2]); break;
         CASE(3,2) dest[0]=compute_y(src[0],src[1],src[2]), dest[1] = 255; break;
         CASE(4,1) dest[0]=compute_y(src[0],src[1],src[2]); break;
         CASE(4,2) dest[0]=compute_y(src[0],src[1],src[2]), dest[1] = src[3]; break;
         CASE(4,3) dest[0]=src[0],dest[1]=src[1],dest[2]=src[2]; break;
         default: assert(0);
      }
      #undef CASE
   }

   free(data);
   img_out_n = req_comp;
   return good;
}



//////////////////////////////////////////////////////////////////////////////
//
//  "baseline" JPEG/JFIF decoder (not actually fully baseline implementation)
//
//    simple implementation
//      - channel subsampling of at most 2 in each dimension
//      - doesn't support delayed output of y-dimension
//      - simple interface (only one output format: 8-bit interleaved RGB)
//      - doesn't try to recover corrupt jpegs
//      - doesn't allow partial loading, loading multiple at once
//      - still fast on x86 (copying globals into locals doesn't help x86)
//      - allocates lots of intermediate memory (full size of all components)
//        - non-interleaved case requires this anyway
//        - allows good upsampling (see next)
//    high-quality
//      - upsampled channels are bilinearly interpolated, even across blocks
//      - quality integer IDCT derived from IJG's 'slow'
//    performance
//      - fast huffman; reasonable integer IDCT
//      - uses a lot of intermediate memory, could cache poorly
//      - load http://nothings.org/remote/anemones.jpg 3 times on 2.8Ghz P4
//          stb_jpeg:   1.34 seconds (MSVC6, default release build)
//          stb_jpeg:   1.06 seconds (MSVC6, processor = Pentium Pro)
//          IJL11.dll:  1.08 seconds (compiled by intel)
//          IJG 1998:   0.98 seconds (MSVC6, makefile provided by IJG)
//          IJG 1998:   0.95 seconds (MSVC6, makefile + proc=PPro)

int stbi_jpeg_dc_only;

// huffman decoding acceleration
#define FAST_BITS   9  // larger handles more cases; smaller stomps less cache

typedef struct
{
   uint8  fast[1 << FAST_BITS];
   // weirdly, repacking this into AoS is a 10% speed loss, instead of a win
   uint16 code[256];
   uint8  values[256];
   uint8  size[257];
   unsigned int maxcode[18];
   int    delta[17];   // old 'firstsymbol' - old 'firstcode'
} huffman;

static huffman huff_dc[4];  // baseline is 2 tables, extended is 4
static huffman huff_ac[4];
static uint8 dequant[4][64];

static int build_huffman(huffman *h, int *count)
{
   int i,j,k=0,code;
   // build size list for each symbol (from JPEG spec)
   for (i=0; i < 16; ++i)
      for (j=0; j < count[i]; ++j)
         h->size[k++] = (uint8) (i+1);
   h->size[k] = 0;

   // compute actual symbols (from jpeg spec)
   code = 0;
   k = 0;
   for(j=1; j <= 16; ++j) {
      // compute delta to add to code to compute symbol id
      h->delta[j] = k - code;
      if (h->size[k] == j) {
         while (h->size[k] == j)
            h->code[k++] = (uint16) (code++);
         if (code-1 >= (1 << j)) return e("bad code lengths","Corrupt JPEG");
      }
      // compute largest code + 1 for this size, preshifted as needed later
      h->maxcode[j] = code << (16-j);
      code <<= 1;
   }
   h->maxcode[j] = 0xffffffff;

   // build non-spec acceleration table; 255 is flag for not-accelerated
   memset(h->fast, 255, 1 << FAST_BITS);
   for (i=0; i < k; ++i) {
      int s = h->size[i];
      if (s <= FAST_BITS) {
         int c = h->code[i] << (FAST_BITS-s);
         int m = 1 << (FAST_BITS-s);
         for (j=0; j < m; ++j) {
            h->fast[c+j] = (uint8) i;
         }
      }
   }
   return 1;
}

// sizes for components, interleaved MCUs
static int img_h_max, img_v_max;
static int img_mcu_x, img_mcu_y;
static int img_mcu_w, img_mcu_h;

// definition of jpeg image component
static struct
{
   int id;
   int h,v;
   int tq;
   int hd,ha;
   int dc_pred;

   int x,y,w2,h2;
   uint8 *data;
} img_comp[4];

static unsigned long  code_buffer; // jpeg entropy-coded buffer
static int            code_bits;   // number of valid bits
static unsigned char  marker;      // marker seen while filling entropy buffer
static int            nomore;      // flag if we saw a marker so must stop
 
static void grow_buffer_unsafe(void)
{
   do {
      int b = nomore ? 0 : get8();
      if (b == 0xff) {
         int c = get8();
         if (c != 0) {
            marker = (unsigned char) c;
            nomore = 1;
            return;
         }
      }
      code_buffer = (code_buffer << 8) | b;
      code_bits += 8;
   } while (code_bits <= 24);
}

// (1 << n) - 1
static unsigned long bmask[17]={0,1,3,7,15,31,63,127,255,511,1023,2047,4095,8191,16383,32767,65535};

// decode a jpeg huffman value from the bitstream
__forceinline static int decode(huffman *h)
{
   unsigned int temp;
   int c,k;

   if (code_bits < 16) grow_buffer_unsafe();

   // look at the top FAST_BITS and determine what symbol ID it is,
   // if the code is <= FAST_BITS
   c = (code_buffer >> (code_bits - FAST_BITS)) & ((1 << FAST_BITS)-1);
   k = h->fast[c];
   if (k < 255) {
      if (h->size[k] > code_bits)
         return -1;
      code_bits -= h->size[k];
      return h->values[k];
   }

   // naive test is to shift the code_buffer down so k bits are
   // valid, then test against maxcode. To speed this up, we've
   // preshifted maxcode left so that it has (16-k) 0s at the
   // end; in other words, regardless of the number of bits, it
   // wants to be compared against something shifted to have 16;
   // that way we don't need to shift inside the loop.
   if (code_bits < 16)
      temp = (code_buffer << (16 - code_bits)) & 0xffff;
   else
      temp = (code_buffer >> (code_bits - 16)) & 0xffff;
   for (k=FAST_BITS+1 ; ; ++k)
      if (temp < h->maxcode[k])
         break;
   if (k == 17) {
      // error! code not found
      code_bits -= 16;
      return -1;
   }

   if (k > code_bits)
      return -1;

   // convert the huffman code to the symbol id
   c = ((code_buffer >> (code_bits - k)) & bmask[k]) + h->delta[k];
   assert((((code_buffer) >> (code_bits - h->size[c])) & bmask[h->size[c]]) == h->code[c]);

   // convert the id to a symbol
   code_bits -= k;
   return h->values[c];
}

// combined JPEG 'receive' and JPEG 'extend', since baseline
// always extends everything it receives.
__forceinline static int extend_receive(int n)
{
   unsigned int m = 1 << (n-1);
   unsigned int k;
   if (code_bits < n) grow_buffer_unsafe();
   k = (code_buffer >> (code_bits - n)) & bmask[n];
   code_bits -= n;
   // the following test is probably a random branch that won't
   // predict well. I tried to table accelerate it but failed.
   // maybe it's compiling as a conditional move?
   if (k < m)
      return (-1 << n) + k + 1;
   else
      return k;
}

// given a value that's at position X in the zigzag stream,
// where does it appear in the 8x8 matrix coded as row-major?
static uint8 dezigzag[64+15] =
{
    0,  1,  8, 16,  9,  2,  3, 10,
   17, 24, 32, 25, 18, 11,  4,  5,
   12, 19, 26, 33, 40, 48, 41, 34,
   27, 20, 13,  6,  7, 14, 21, 28,
   35, 42, 49, 56, 57, 50, 43, 36,
   29, 22, 15, 23, 30, 37, 44, 51,
   58, 59, 52, 45, 38, 31, 39, 46,
   53, 60, 61, 54, 47, 55, 62, 63,
   // let corrupt input sample past end
   63, 63, 63, 63, 63, 63, 63, 63,
   63, 63, 63, 63, 63, 63, 63
};

// decode one 64-entry block--
static int decode_block(short data[64], huffman *hdc, huffman *hac, int b)
{
   int diff,dc,k;
   int t = decode(hdc);
   if (t < 0) return e("bad huffman code","Corrupt JPEG");

   // 0 all the ac values now so we can do it 32-bits at a time
   memset(data,0,64*sizeof(data[0]));

   diff = t ? extend_receive(t) : 0;
   dc = img_comp[b].dc_pred + diff;
   img_comp[b].dc_pred = dc;
   data[0] = (short) dc;

   // decode AC components, see JPEG spec
   k = 1;
   do {
      int r,s;
      int rs = decode(hac);
      if (rs < 0) return e("bad huffman code","Corrupt JPEG");
      s = rs & 15;
      r = rs >> 4;
      if (s == 0) {
         if (rs != 0xf0) break; // end block
         k += 16;
      } else {
         k += r;
         // decode into unzigzag'd location
         data[dezigzag[k++]] = (short) extend_receive(s);
      }
   } while (k < 64);
   return 1;
}

// take a -128..127 value and clamp it and convert to 0..255
__forceinline static uint8 clamp(int x)
{
   x += 128;
   // trick to use a single test to catch both cases
   if ((unsigned int) x > 255) {
      if (x < 0) return 0;
      if (x > 255) return 255;
   }
   return (uint8) x;
}

#define f2f(x)  (int) (((x) * 4096 + 0.5))
#define fsh(x)  ((x) << 12)

// derived from jidctint -- DCT_ISLOW
#define IDCT_1D(s0,s1,s2,s3,s4,s5,s6,s7)       \
   int t0,t1,t2,t3,p1,p2,p3,p4,p5,x0,x1,x2,x3; \
   p2 = s2;                                    \
   p3 = s6;                                    \
   p1 = (p2+p3) * f2f(0.5411961f);             \
   t2 = p1 + p3*f2f(-1.847759065f);            \
   t3 = p1 + p2*f2f( 0.765366865f);            \
   p2 = s0;                                    \
   p3 = s4;                                    \
   t0 = fsh(p2+p3);                            \
   t1 = fsh(p2-p3);                            \
   x0 = t0+t3;                                 \
   x3 = t0-t3;                                 \
   x1 = t1+t2;                                 \
   x2 = t1-t2;                                 \
   t0 = s7;                                    \
   t1 = s5;                                    \
   t2 = s3;                                    \
   t3 = s1;                                    \
   p3 = t0+t2;                                 \
   p4 = t1+t3;                                 \
   p1 = t0+t3;                                 \
   p2 = t1+t2;                                 \
   p5 = (p3+p4)*f2f( 1.175875602f);            \
   t0 = t0*f2f( 0.298631336f);                 \
   t1 = t1*f2f( 2.053119869f);                 \
   t2 = t2*f2f( 3.072711026f);                 \
   t3 = t3*f2f( 1.501321110f);                 \
   p1 = p5 + p1*f2f(-0.899976223f);            \
   p2 = p5 + p2*f2f(-2.562915447f);            \
   p3 = p3*f2f(-1.961570560f);                 \
   p4 = p4*f2f(-0.390180644f);                 \
   t3 += p1+p4;                                \
   t2 += p2+p3;                                \
   t1 += p2+p4;                                \
   t0 += p1+p3;

// .344 seconds on 3*anemones.jpg
static void idct_block(uint8 *out, int out_stride, short data[64], uint8 *dequantize)
{
   int i,val[64],*v=val;
   uint8 *o,*dq = dequantize;
   short *d = data;

   if (stbi_jpeg_dc_only) {
      // ok, I don't really know why this is right, but it seems to be:
      int z = 128 + ((d[0] * dq[0]) >> 3);
      for (i=0; i < 8; ++i) {
         out[0] = out[1] = out[2] = out[3] = out[4] = out[5] = out[6] = out[7] = z;
         out += out_stride;
      }
      return;
   }

   // columns
   for (i=0; i < 8; ++i,++d,++dq, ++v) {
      // if all zeroes, shortcut -- this avoids dequantizing 0s and IDCTing
      if (d[ 8]==0 && d[16]==0 && d[24]==0 && d[32]==0
           && d[40]==0 && d[48]==0 && d[56]==0) {
         //    no shortcut                 0     seconds
         //    (1|2|3|4|5|6|7)==0          0     seconds
         //    all separate               -0.047 seconds
         //    1 && 2|3 && 4|5 && 6|7:    -0.047 seconds
         int dcterm = d[0] * dq[0] << 2;
         v[0] = v[8] = v[16] = v[24] = v[32] = v[40] = v[48] = v[56] = dcterm;
      } else {
         IDCT_1D(d[ 0]*dq[ 0],d[ 8]*dq[ 8],d[16]*dq[16],d[24]*dq[24],
                 d[32]*dq[32],d[40]*dq[40],d[48]*dq[48],d[56]*dq[56])
         // constants scaled things up by 1<<12; let's bring them back
         // down, but keep 2 extra bits of precision
         x0 += 512; x1 += 512; x2 += 512; x3 += 512;
         v[ 0] = (x0+t3) >> 10;
         v[56] = (x0-t3) >> 10;
         v[ 8] = (x1+t2) >> 10;
         v[48] = (x1-t2) >> 10;
         v[16] = (x2+t1) >> 10;
         v[40] = (x2-t1) >> 10;
         v[24] = (x3+t0) >> 10;
         v[32] = (x3-t0) >> 10;
      }
   }

   for (i=0, v=val, o=out; i < 8; ++i,v+=8,o+=out_stride) {
      // no fast case since the first 1D IDCT spread components out
      IDCT_1D(v[0],v[1],v[2],v[3],v[4],v[5],v[6],v[7])
      // constants scaled things up by 1<<12, plus we had 1<<2 from first
      // loop, plus horizontal and vertical each scale by sqrt(8) so together
      // we've got an extra 1<<3, so 1<<17 total we need to remove.
      x0 += 65536; x1 += 65536; x2 += 65536; x3 += 65536;
      o[0] = clamp((x0+t3) >> 17);
      o[7] = clamp((x0-t3) >> 17);
      o[1] = clamp((x1+t2) >> 17);
      o[6] = clamp((x1-t2) >> 17);
      o[2] = clamp((x2+t1) >> 17);
      o[5] = clamp((x2-t1) >> 17);
      o[3] = clamp((x3+t0) >> 17);
      o[4] = clamp((x3-t0) >> 17);
   }
}

#define MARKER_none  0xff
// if there's a pending marker from the entropy stream, return that
// otherwise, fetch from the stream and get a marker. if there's no
// marker, return 0xff, which is never a valid marker value
static uint8 get_marker(void)
{
   uint8 x;
   if (marker != MARKER_none) { x = marker; marker = MARKER_none; return x; }
   x = get8u();
   if (x != 0xff) return MARKER_none;
   while (x == 0xff)
      x = get8u();
   return x;
}

// in each scan, we'll have scan_n components, and the order
// of the components is specified by order[]
static int scan_n, order[4];
static int restart_interval, todo;
#define RESTART(x)     ((x) >= 0xd0 && (x) <= 0xd7)

// after a restart interval, reset the entropy decoder and
// the dc prediction
static void reset(void)
{
   code_bits = 0;
   code_buffer = 0;
   nomore = 0;
   img_comp[0].dc_pred = img_comp[1].dc_pred = img_comp[2].dc_pred = 0;
   marker = MARKER_none;
   todo = restart_interval ? restart_interval : 0x7fffffff;
   // no more than 1<<31 MCUs if no restart_interal? that's plenty safe,
   // since we don't even allow 1<<30 pixels
}

static int parse_entropy_coded_data(void)
{
   reset();
   if (scan_n == 1) {
      int i,j;
      short data[64];
      int n = order[0];
      // non-interleaved data, we just need to process one block at a time,
      // in trivial scanline order
      // number of blocks to do just depends on how many actual "pixels" this
      // component has, independent of interleaved MCU blocking and such
      int w = (img_comp[n].x+7) >> 3;
      int h = (img_comp[n].y+7) >> 3;
      for (j=0; j < h; ++j) {
         for (i=0; i < w; ++i) {
            if (!decode_block(data, huff_dc+img_comp[n].hd, huff_ac+img_comp[n].ha, n)) return 0;
            idct_block(img_comp[n].data+img_comp[n].w2*j*8+i*8, img_comp[n].w2, data, dequant[img_comp[n].tq]);
            // every data block is an MCU, so countdown the restart interval
            if (--todo <= 0) {
               if (code_bits < 24) grow_buffer_unsafe();
               // if it's NOT a restart, then just bail, so we get corrupt data
               // rather than no data
               if (!RESTART(marker)) return 1;
               reset();
            }
         }
      }
   } else { // interleaved!
      int i,j,k,x,y;
      short data[64];
      for (j=0; j < img_mcu_y; ++j) {
         for (i=0; i < img_mcu_x; ++i) {
            // scan an interleaved mcu... process scan_n components in order
            for (k=0; k < scan_n; ++k) {
               int n = order[k];
               // scan out an mcu's worth of this component; that's just determined
               // by the basic H and V specified for the component
               for (y=0; y < img_comp[n].v; ++y) {
                  for (x=0; x < img_comp[n].h; ++x) {
                     int x2 = (i*img_comp[n].h + x)*8;
                     int y2 = (j*img_comp[n].v + y)*8;
                     if (!decode_block(data, huff_dc+img_comp[n].hd, huff_ac+img_comp[n].ha, n)) return 0;
                     idct_block(img_comp[n].data+img_comp[n].w2*y2+x2, img_comp[n].w2, data, dequant[img_comp[n].tq]);
                  }
               }
            }
            // after all interleaved components, that's an interleaved MCU,
            // so now count down the restart interval
            if (--todo <= 0) {
               if (code_bits < 24) grow_buffer_unsafe();
               // if it's NOT a restart, then just bail, so we get corrupt data
               // rather than no data
               if (!RESTART(marker)) return 1;
               reset();
            }
         }
      }
   }
   return 1;
}

static int process_marker(int m)
{
   int L;
   switch (m) {
      case MARKER_none: // no marker found
         return e("expected marker","Corrupt JPEG");

      case 0xC2: // SOF - progressive
         return e("progressive jpeg","JPEG format not supported (progressive)");

      case 0xDD: // DRI - specify restart interval
         if (get16() != 4) return e("bad DRI len","Corrupt JPEG");
         restart_interval = get16();
         return 1;

      case 0xDB: // DQT - define quantization table
         L = get16()-2;
         while (L > 0) {
            int z = get8();
            int p = z >> 4;
            int t = z & 15,i;
            if (p != 0) return e("bad DQT type","Corrupt JPEG");
            if (t > 3) return e("bad DQT table","Corrupt JPEG");
            for (i=0; i < 64; ++i)
               dequant[t][dezigzag[i]] = get8u();
            L -= 65;
         }
         return L==0;

      case 0xC4: // DHT - define huffman table
         L = get16()-2;
         while (L > 0) {
            uint8 *v;
            int sizes[16],i,m=0;
            int z = get8();
            int tc = z >> 4;
            int th = z & 15;
            if (tc > 1 || th > 3) return e("bad DHT header","Corrupt JPEG");
            for (i=0; i < 16; ++i) {
               sizes[i] = get8();
               m += sizes[i];
            }
            L -= 17;
            if (tc == 0) {
               if (!build_huffman(huff_dc+th, sizes)) return 0;
               v = huff_dc[th].values;
            } else {
               if (!build_huffman(huff_ac+th, sizes)) return 0;
               v = huff_ac[th].values;
            }
            for (i=0; i < m; ++i)
               v[i] = get8u();
            L -= m;
         }
         return L==0;
   }
   // check for comment block or APP blocks
   if ((m >= 0xE0 && m <= 0xEF) || m == 0xFE) {
      skip(get16()-2);
      return 1;
   }
   return 0;
}

// after we see SOS
static int process_scan_header(void)
{
   int i;
   int Ls = get16();
   scan_n = get8();
   if (scan_n < 1 || scan_n > 4 || scan_n > (int) img_n) return e("bad SOS component count","Corrupt JPEG");
   if (Ls != 6+2*scan_n) return e("bad SOS len","Corrupt JPEG");
   for (i=0; i < scan_n; ++i) {
      int id = get8(), which;
      int z = get8();
      for (which = 0; which < img_n; ++which)
         if (img_comp[which].id == id)
            break;
      if (which == img_n) return 0;
      img_comp[which].hd = z >> 4;   if (img_comp[which].hd > 3) return e("bad DC huff","Corrupt JPEG");
      img_comp[which].ha = z & 15;   if (img_comp[which].ha > 3) return e("bad AC huff","Corrupt JPEG");
      order[i] = which;
   }
   if (get8() != 0) return e("bad SOS","Corrupt JPEG");
   get8(); // should be 63, but might be 0
   if (get8() != 0) return e("bad SOS","Corrupt JPEG");

   return 1;
}

static int process_frame_header(int scan)
{
   int Lf,p,i,z, h_max=1,v_max=1;
   Lf = get16();         if (Lf < 11) return e("bad SOF len","Corrupt JPEG"); // JPEG
   p  = get8();          if (p != 8) return e("only 8-bit","JPEG format not supported: 8-bit only"); // JPEG baseline
   img_y = get16();      if (img_y == 0) return e("no header height", "JPEG format not supported: delayed height"); // Legal, but we don't handle it--but neither does IJG
   img_x = get16();      if (img_x == 0) return e("0 width","Corrupt JPEG"); // JPEG requires
   img_n = get8();
   if (img_n != 3 && img_n != 1) return e("bad component count","Corrupt JPEG");    // JFIF requires

   if (Lf != 8+3*img_n) return e("bad SOF len","Corrupt JPEG");

   for (i=0; i < img_n; ++i) {
      img_comp[i].id = get8();
      if (img_comp[i].id != i+1)   // JFIF requires
         if (img_comp[i].id != i)  // jpegtran outputs non-JFIF-compliant files!
            return e("bad component ID","Corrupt JPEG");
      z = get8();
      img_comp[i].h = (z >> 4);  if (!img_comp[i].h || img_comp[i].h > 4) return e("bad H","Corrupt JPEG");
      img_comp[i].v = z & 15;    if (!img_comp[i].h || img_comp[i].h > 4) return e("bad V","Corrupt JPEG");
      img_comp[i].tq = get8();   if (img_comp[i].tq > 3) return e("bad TQ","Corrupt JPEG");
   }

   if (scan != SCAN_load) return 1;

   for (i=0; i < img_n; ++i) {
      if (img_comp[i].h > h_max) h_max = img_comp[i].h;
      if (img_comp[i].v > v_max) v_max = img_comp[i].v;
   }

   // compute interleaved mcu info
   img_h_max = h_max;
   img_v_max = v_max;
   img_mcu_w = h_max * 8;
   img_mcu_h = v_max * 8;
   img_mcu_x = (img_x + img_mcu_w-1) / img_mcu_w;
   img_mcu_y = (img_y + img_mcu_h-1) / img_mcu_h;

   for (i=0; i < img_n; ++i) {
      // number of effective pixels (e.g. for non-interleaved MCU)
      img_comp[i].x = (img_x * img_comp[i].h + h_max-1) / h_max;
      img_comp[i].y = (img_y * img_comp[i].v + v_max-1) / v_max;
      // to simplify generation, we'll allocate enough memory to decode
      // the bogus oversized data from using interleaved MCUs and their
      // big blocks (e.g. a 16x16 iMCU on an image of width 33); we won't
      // discard the extra data until colorspace conversion
      img_comp[i].w2 = img_mcu_x * img_comp[i].h * 8;
      img_comp[i].h2 = img_mcu_y * img_comp[i].v * 8;
      img_comp[i].data = (uint8 *) malloc(img_comp[i].w2 * img_comp[i].h2);
   }

   return 1;
}

// use comparisons since in some cases we handle more than one case (e.g. SOF)
#define DNL(x)         ((x) == 0xdc)
#define SOI(x)         ((x) == 0xd8)
#define EOI(x)         ((x) == 0xd9)
#define SOF(x)         ((x) == 0xc0 || (x) == 0xc1)
#define SOS(x)         ((x) == 0xda)

static int decode_jpeg_header(int scan)
{
   int m;
   marker = MARKER_none; // initialize cached marker to empty
   m = get_marker();
   if (!SOI(m)) return e("no SOI","Corrupt JPEG");
   if (scan == SCAN_type) return 1;
   m = get_marker();
   while (!SOF(m)) {
      if (!process_marker(m)) return 0;
      m = get_marker();
      while (m == MARKER_none) {
         // some files have extra padding after their blocks, so ok, we'll scan
         if (at_eof()) return e("no SOF", "Corrupt JPEG");
         m = get_marker();
      }
   }
   if (!process_frame_header(scan)) return 0;
   return 1;
}

static int decode_jpeg_image(void)
{
   int m;
   restart_interval = 0;
   if (!decode_jpeg_header(SCAN_load)) return 0;
   m = get_marker();
   while (!EOI(m)) {
      if (SOS(m)) {
         if (!process_scan_header()) return 0;
         if (!parse_entropy_coded_data()) return 0;
      } else {
         if (!process_marker(m)) return 0;
      }
      m = get_marker();
   }
   return 1;
}

// static jfif-centered resampling with cross-block smoothing
// here by cross-block smoothing what I mean is that the resampling
// is bilerp and crosses blocks; I dunno what IJG means

#define div4(x) ((uint8) ((x) >> 2))

static void resample_v_2(uint8 *out1, uint8 *input, int w, int h, int s)
{
   // need to generate two samples vertically for every one in input
   uint8 *above;
   uint8 *below;
   uint8 *source;
   uint8 *out2;
   int i,j;
   source = input;
   out2 = out1+w;
   for (j=0; j < h; ++j) {
      above = source;
      source = input + j*s;
      below = source + s; if (j == h-1) below = source;
      for (i=0; i < w; ++i) {
         int n = source[i]*3;
         out1[i] = div4(above[i] + n);
         out2[i] = div4(below[i] + n);
      }
      out1 += w*2;
      out2 += w*2;
   }
}

static void resample_h_2(uint8 *out, uint8 *input, int w, int h, int s)
{
   // need to generate two samples horizontally for every one in input
   int i,j;
   if (w == 1) {
      for (j=0; j < h; ++j)
         out[j*2+0] = out[j*2+1] = input[j*s];
      return;
   }
   for (j=0; j < h; ++j) {
      out[0] = input[0];
      out[1] = div4(input[0]*3 + input[1]);
      for (i=1; i < w-1; ++i) {
         int n = input[i]*3;
         out[i*2-2] = div4(input[i-1] + n);
         out[i*2-1] = div4(input[i+1] + n);
      }
      out[w*2-2] = div4(input[w-2]*3 + input[w-1]);
      out[w*2-1] = input[w-1];
      out += w*2;
      input += s;
   }
}

// .172 seconds on 3*anemones.jpg
static void resample_hv_2(uint8 *out, uint8 *input, int w, int h, int s)
{
   // need to generate 2x2 samples for every one in input
   int i,j;
   int os = w*2;
   // generate edge samples... @TODO lerp them!
   for (i=0; i < w; ++i) {
      out[i*2+0] = out[i*2+1] = input[i];
      out[i*2+(2*h-1)*os+0] = out[i*2+(2*h-1)*os+1] = input[i+(h-1)*w];
   }
   for (j=0; j < h; ++j) {
      out[j*os*2+0] = out[j*os*2+os+0] = input[j*w];
      out[j*os*2+os-1] = out[j*os*2+os+os-1] = input[j*w+i-1];
   }
   // now generate interior samples; i & j point to top left of input
   for (j=0; j < h-1; ++j) {
      uint8 *in1 = input+j*s;
      uint8 *in2 = in1 + s;
      uint8 *out1 = out + (j*2+1)*os + 1;
      uint8 *out2 = out1 + os;
      for (i=0; i < w-1; ++i) {
         int p00 = in1[0], p01=in1[1], p10=in2[0], p11=in2[1];
         int p00_3 = p00*3, p01_3 = p01*3, p10_3 = p10*3, p11_3 = p11*3;

         #define div16(x)  ((uint8) ((x) >> 4))

         out1[0] = div16(p00*9 + p01_3 + p10_3 + p11);
         out1[1] = div16(p01*9 + p00_3 + p01_3 + p10);
         out2[0] = div16(p10*9 + p11_3 + p00_3 + p01);
         out2[1] = div16(p11*9 + p10_3 + p01_3 + p00);
         out1 += 2;
         out2 += 2;                                                         
         ++in1;
         ++in2;
      }
   }
}

#define float2fixed(x)  ((int) ((x) * 65536 + 0.5))

// 0.38 seconds on 3*anemones.jpg   (0.25 with processor = Pro)
// VC6 without processor=Pro is generating multiple LEAs per multiply!
static void YCbCr_to_RGB_row(uint8 *out, uint8 *y, uint8 *pcb, uint8 *pcr, int count, int step)
{
   int i;
   for (i=0; i < count; ++i) {
      int y_fixed = (y[i] << 16) + 32768; // rounding
      int r,g,b;
      int cr = pcr[i] - 128;
      int cb = pcb[i] - 128;
      r = y_fixed + cr*float2fixed(1.40200f);
      g = y_fixed - cr*float2fixed(0.71414f) - cb*float2fixed(0.34414f);
      b = y_fixed                            + cb*float2fixed(1.77200f);
      r >>= 16;
      g >>= 16;
      b >>= 16;
      if ((unsigned) r > 255) { if (r < 0) r = 0; else r = 255; }
      if ((unsigned) g > 255) { if (g < 0) g = 0; else g = 255; }
      if ((unsigned) b > 255) { if (b < 0) b = 0; else b = 255; }
      out[0] = (uint8)r;
      out[1] = (uint8)g;
      out[2] = (uint8)b;
      if (step == 4) out[3] = 255;
      out += step;
   }
}

// clean up the temporary component buffers
static void cleanup_jpeg(void)
{
   int i;
   for (i=0; i < img_n; ++i) {
      if (img_comp[i].data) {
         free(img_comp[i].data);
         img_comp[i].data = NULL;
      }
   }
}

static uint8 *load_jpeg_image(int *out_x, int *out_y, int *comp, int req_comp)
{
   int i, n;
   // validate req_comp
   if (req_comp < 0 || req_comp > 4) return ep("bad req_comp", "Internal error");

   // load a jpeg image from whichever source
   if (!decode_jpeg_image()) { cleanup_jpeg(); return NULL; }

   // determine actual number of components to generate
   n = req_comp ? req_comp : img_n;

   // resample components to full size... memory wasteful, but this
   // lets us bilerp across blocks while upsampling
   for (i=0; i < img_n; ++i) {
      // if we're outputting fewer than 3 components, we're grey not RGB;
      // in that case, don't bother upsampling Cb or Cr
      if (n < 3 && i) continue;

      // check if the component scale is less than max; if so it needs upsampling
      if (img_comp[i].h != img_h_max || img_comp[i].v != img_v_max) {
         int stride = img_x;
         // allocate final size; make sure it's big enough for upsampling off
         // the edges with upsample up to 4x4 (although we only support 2x2
         // currently)
         uint8 *new_data = (uint8 *) malloc((img_x+3)*(img_y+3));
         if (img_comp[i].h*2 == img_h_max && img_comp[i].v*2 == img_v_max) {
            int tx = (img_x+1)>>1;
            resample_hv_2(new_data, img_comp[i].data, tx,(img_y+1)>>1, img_comp[i].w2);
            stride = tx*2;
         } else if (img_comp[i].h == img_h_max && img_comp[i].v*2 == img_v_max) {
            resample_v_2(new_data, img_comp[i].data, img_x,(img_y+1)>>1, img_comp[i].w2);
         } else if (img_comp[i].h*2 == img_h_max && img_comp[i].v == img_v_max) {
            int tx = (img_x+1)>>1;
            resample_h_2(new_data, img_comp[i].data, tx,img_y, img_comp[i].w2);
            stride = tx*2;
         } else {
            // @TODO resample uncommon sampling pattern with nearest neighbor
            free(new_data);
            cleanup_jpeg();
            return ep("uncommon H or V", "JPEG not supported: atypical downsampling mode");
         }
         img_comp[i].w2 = stride;
         free(img_comp[i].data);
         img_comp[i].data = new_data;
      }
   }

   // now convert components to output image
   {
      uint32 i,j;
      uint8 *output = (uint8 *) malloc(n * img_x * img_y + 1);
      if (n >= 3) { // output STBI_rgb_*
         for (j=0; j < img_y; ++j) {
            uint8 *y  = img_comp[0].data + j*img_comp[0].w2;
            uint8 *out = output + n * img_x * j;
            if (img_n == 3) {
               uint8 *cb = img_comp[1].data + j*img_comp[1].w2;
               uint8 *cr = img_comp[2].data + j*img_comp[2].w2;
               YCbCr_to_RGB_row(out, y, cb, cr, img_x, n);
            } else {
               for (i=0; i < img_x; ++i) {
                  out[0] = out[1] = out[2] = y[i];
                  out[3] = 255; // not used if n == 3
                  out += n;
               }
            }
         }
      } else {      // output STBI_grey_*
         for (j=0; j < img_y; ++j) {
            uint8 *y  = img_comp[0].data + j*img_comp[0].w2;
            uint8 *out = output + n * img_x * j;
            if (n == 1)
               for (i=0; i < img_x; ++i) *out++ = *y++;
            else
               for (i=0; i < img_x; ++i) *out++ = *y++, *out++ = 255;
         }
      }
      cleanup_jpeg();
      *out_x = img_x;
      *out_y = img_y;
      if (comp) *comp  = img_n; // report original components, not output
      return output;
   }
}

#ifndef STBI_NO_STDIO
unsigned char *stbi_jpeg_load_from_file(FILE *f, int *x, int *y, int *comp, int req_comp)
{
   start_file(f);
   return load_jpeg_image(x,y,comp,req_comp);
}

unsigned char *stbi_jpeg_load(char *filename, int *x, int *y, int *comp, int req_comp)
{
   unsigned char *data;
   FILE *f = fopen(filename, "rb");
   if (!f) return NULL;
   data = stbi_jpeg_load_from_file(f,x,y,comp,req_comp);
   fclose(f);
   return data;
}
#endif

unsigned char *stbi_jpeg_load_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp)
{
   start_mem(buffer,len);
   return load_jpeg_image(x,y,comp,req_comp);
}

#ifndef STBI_NO_STDIO
int stbi_jpeg_test_file(FILE *f)
{
   int n,r;
   n = ftell(f);
   start_file(f);
   r = decode_jpeg_header(SCAN_type);
   fseek(f,n,SEEK_SET);
   return r;
}
#endif

int stbi_jpeg_test_memory(unsigned char *buffer, int len)
{
   start_mem(buffer,len);
   return decode_jpeg_header(SCAN_type);
}

// @TODO:
extern int      stbi_jpeg_info            (char *filename,           int *x, int *y, int *comp);
extern int      stbi_jpeg_info_from_file  (FILE *f,                  int *x, int *y, int *comp);
extern int      stbi_jpeg_info_from_memory(stbi_uc *buffer, int len, int *x, int *y, int *comp);

// public domain zlib decode    v0.2  Sean Barrett 2006-11-18
//    simple implementation
//      - all input must be provided in an upfront buffer
//      - all output is written to a single output buffer (can malloc/realloc)
//    performance
//      - fast huffman

// fast-way is faster to check than jpeg huffman, but slow way is slower
#define ZFAST_BITS  9 // accelerate all cases in default tables
#define ZFAST_MASK  ((1 << ZFAST_BITS) - 1)

// zlib-style huffman encoding
// (jpegs packs from left, zlib from right, so can't share code)
typedef struct
{
   uint16 fast[1 << ZFAST_BITS];
   uint16 firstcode[16];
   int maxcode[17];
   uint16 firstsymbol[16];
   uint8  size[288];
   uint16 value[288]; 
} zhuffman;

__forceinline static int bitreverse16(int n)
{
  n = ((n & 0xAAAA) >>  1) | ((n & 0x5555) << 1);
  n = ((n & 0xCCCC) >>  2) | ((n & 0x3333) << 2);
  n = ((n & 0xF0F0) >>  4) | ((n & 0x0F0F) << 4);
  n = ((n & 0xFF00) >>  8) | ((n & 0x00FF) << 8);
  return n;
}

__forceinline static int bit_reverse(int v, int bits)
{
   assert(bits <= 16);
   // to bit reverse n bits, reverse 16 and shift
   // e.g. 11 bits, bit reverse and shift away 5
   return bitreverse16(v) >> (16-bits);
}

static int zbuild_huffman(zhuffman *z, uint8 *sizelist, int num)
{
   int i,k=0;
   int code, next_code[16], sizes[17];

   // DEFLATE spec for generating codes
   memset(sizes, 0, sizeof(sizes));
   memset(z->fast, 255, sizeof(z->fast));
   for (i=0; i < num; ++i) 
      ++sizes[sizelist[i]];
   sizes[0] = 0;
   for (i=1; i < 16; ++i)
      assert(sizes[i] <= (1 << i));
   code = 0;
   for (i=1; i < 16; ++i) {
      next_code[i] = code;
      z->firstcode[i] = (uint16) code;
      z->firstsymbol[i] = (uint16) k;
      code = (code + sizes[i]);
      if (sizes[i])
         if (code-1 >= (1 << i)) return e("bad codelengths","Corrupt JPEG");
      z->maxcode[i] = code << (16-i); // preshift for inner loop
      code <<= 1;
      k += sizes[i];
   }
   z->maxcode[16] = 0x10000; // sentinel
   for (i=0; i < num; ++i) {
      int s = sizelist[i];
      if (s) {
         int c = next_code[s] - z->firstcode[s] + z->firstsymbol[s];
         z->size[c] = (uint8)s;
         z->value[c] = (uint16)i;
         if (s <= ZFAST_BITS) {
            int k = bit_reverse(next_code[s],s);
            while (k < (1 << ZFAST_BITS)) {
               z->fast[k] = (uint16) c;
               k += (1 << s);
            }
         }
         ++next_code[s];
      }
   }
   return 1;
}

// zlib-from-memory implementation for PNG reading
//    because PNG allows splitting the zlib stream arbitrarily,
//    and it's annoying structurally to have PNG call ZLIB call PNG,
//    we require PNG read all the IDATs and combine them into a single
//    memory buffer

static uint8 *zbuffer, *zbuffer_end;

__forceinline static int zget8(void)
{
   if (zbuffer >= zbuffer_end) return 0;
   return *zbuffer++;
}

//static unsigned long code_buffer;
static int           num_bits;

static void fill_bits(void)
{
   do {
      assert(code_buffer < (1U << num_bits));
      code_buffer |= zget8() << num_bits;
      num_bits += 8;
   } while (num_bits <= 24);
}

__forceinline static unsigned int zreceive(int n)
{
   unsigned int k;
   if (num_bits < n) fill_bits();
   k = code_buffer & ((1 << n) - 1);
   code_buffer >>= n;
   num_bits -= n;
   return k;   
}

__forceinline static int zhuffman_decode(zhuffman *z)
{
   int b,s,k;
   if (num_bits < 16) fill_bits();
   b = z->fast[code_buffer & ZFAST_MASK];
   if (b < 0xffff) {
      s = z->size[b];
      code_buffer >>= s;
      num_bits -= s;
      return z->value[b];
   }

   // not resolved by fast table, so compute it the slow way
   // use jpeg approach, which requires MSbits at top
   k = bit_reverse(code_buffer, 16);
   for (s=ZFAST_BITS+1; ; ++s)
      if (k < z->maxcode[s])
         break;
   if (s == 16) return -1; // invalid code!
   // code size is s, so:
   b = (k >> (16-s)) - z->firstcode[s] + z->firstsymbol[s];
   assert(z->size[b] == s);
   code_buffer >>= s;
   num_bits -= s;
   return z->value[b];
}

static char *zout;
static char *zout_start;
static char *zout_end;
static int   z_expandable;

static int expand(int n)  // need to make room for n bytes
{
   char *q;
   int cur, limit;
   if (!z_expandable) return e("output buffer limit","Corrupt PNG");
   cur   = (int) (zout     - zout_start);
   limit = (int) (zout_end - zout_start);
   while (cur + n > limit)
      limit *= 2;
   q = (char *) realloc(zout_start, limit);
   if (q == NULL) return e("outofmem", "Out of memory");
   zout_start = q;
   zout       = q + cur;
   zout_end   = q + limit;
   return 1;
}

static zhuffman z_length, z_distance;

static int length_base[31] = {
   3,4,5,6,7,8,9,10,11,13,
   15,17,19,23,27,31,35,43,51,59,
   67,83,99,115,131,163,195,227,258,0,0 };

static int length_extra[31]= 
{ 0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0,0,0 };

static int dist_base[32] = { 1,2,3,4,5,7,9,13,17,25,33,49,65,97,129,193,
257,385,513,769,1025,1537,2049,3073,4097,6145,8193,12289,16385,24577,0,0};

static int dist_extra[32] =
{ 0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13};

static int parse_huffman_block(void)
{
   for(;;) {
      int z = zhuffman_decode(&z_length);
      if (z < 256) {
         if (z < 0) return e("bad huffman code","Corrupt PNG"); // error in huffman codes
         if (zout >= zout_end) if (!expand(1)) return 0;
         *zout++ = (char) z;
      } else {
         uint8 *p;
         int len,dist;
         if (z == 256) return 1;
         z -= 257;
         len = length_base[z];
         if (length_extra[z]) len += zreceive(length_extra[z]);
         z = zhuffman_decode(&z_distance);
         if (z < 0) return e("bad huffman code","Corrupt PNG");
         dist = dist_base[z];
         if (dist_extra[z]) dist += zreceive(dist_extra[z]);
         if (zout - zout_start < dist) return e("bad dist","Corrupt PNG");
         if (zout + len > zout_end) if (!expand(len)) return 0;
         p = (uint8 *) (zout - dist);
         while (len--)
            *zout++ = *p++;
      }
   }
}

static int compute_huffman_codes(void)
{
   static uint8 length_dezigzag[19] = { 16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15 };
   static zhuffman z_codelength; // static just to save stack space
   uint8 lencodes[286+32+137];//padding for maximum single op
   uint8 codelength_sizes[19];
   int i,n;

   int hlit  = zreceive(5) + 257;
   int hdist = zreceive(5) + 1;
   int hclen = zreceive(4) + 4;

   memset(codelength_sizes, 0, sizeof(codelength_sizes));
   for (i=0; i < hclen; ++i) {
      int s = zreceive(3);
      codelength_sizes[length_dezigzag[i]] = (uint8) s;
   }
   if (!zbuild_huffman(&z_codelength, codelength_sizes, 19)) return 0;

   n = 0;
   while (n < hlit + hdist) {
      int c = zhuffman_decode(&z_codelength);
      assert(c >= 0 && c < 19);
      if (c < 16)
         lencodes[n++] = (uint8) c;
      else if (c == 16) {
         c = zreceive(2)+3;
         memset(lencodes+n, lencodes[n-1], c);
         n += c;
      } else if (c == 17) {
         c = zreceive(3)+3;
         memset(lencodes+n, 0, c);
         n += c;
      } else {
         assert(c == 18);
         c = zreceive(7)+11;
         memset(lencodes+n, 0, c);
         n += c;
      }
   }
   if (n != hlit+hdist) return e("bad codelengths","Corrupt PNG");
   if (!zbuild_huffman(&z_length, lencodes, hlit)) return 0;
   if (!zbuild_huffman(&z_distance, lencodes+hlit, hdist)) return 0;
   return 1;
}

static int parse_uncompressed_block(void)
{
   uint8 header[4];
   int len,nlen,k;
   if (num_bits & 7)
      zreceive(num_bits & 7); // discard
   // drain the bit-packed data into header
   k = 0;
   while (num_bits > 0) {
      header[k++] = (uint8) (code_buffer & 255); // wtf this warns?
      code_buffer >>= 8;
      num_bits -= 8;
   }
   assert(num_bits == 0);
   // now fill header the normal way
   while (k < 4)
      header[k++] = (uint8) zget8();
   len  = header[1] * 256 + header[0];
   nlen = header[3] * 256 + header[2];
   if (nlen != (len ^ 0xffff)) return e("zlib corrupt","Corrupt PNG");
   if (zbuffer + len > zbuffer_end) return e("read past buffer","Corrupt PNG");
   if (zout + len > zout_end)
      if (!expand(len)) return 0;
   memcpy(zout, zbuffer, len);
   zbuffer += len;
   zout += len;
   return 1;
}

static int parse_zlib_header(void)
{
   int cmf   = zget8();
   int cm    = cmf & 15;
   /* int cinfo = cmf >> 4; */
   int flg   = zget8();
   if ((cmf*256+flg) % 31 != 0) return e("bad zlib header","Corrupt PNG"); // zlib spec
   if (flg & 32) return e("no preset dict","Corrupt PNG"); // preset dictionary not allowed in png
   if (cm != 8) return e("bad compression","Corrupt PNG"); // DEFLATE required for png
   // window = 1 << (8 + cinfo)... but who cares, we fully buffer output
   return 1;
}

static uint8 default_length[288], default_distance[32];
static void init_defaults(void)
{
   int i;   // use <= to match clearly with spec
   for (i=0; i <= 143; ++i)     default_length[i]   = 8;
   for (   ; i <= 255; ++i)     default_length[i]   = 9;
   for (   ; i <= 279; ++i)     default_length[i]   = 7;
   for (   ; i <= 287; ++i)     default_length[i]   = 8;

   for (i=0; i <=  31; ++i)     default_distance[i] = 5;
}

static int parse_zlib(void)
{
   int final, type;
   if (!parse_zlib_header()) return 0;
   num_bits = 0;
   code_buffer = 0;
   do {
      final = zreceive(1);
      type = zreceive(2);
      if (type == 0) {
         if (!parse_uncompressed_block()) return 0;
      } else if (type == 3) {
         return 0;
      } else {
         if (type == 1) {
            // use fixed code lengths
            if (!default_length[0]) init_defaults();
            if (!zbuild_huffman(&z_length  , default_length  , 288)) return 0;
            if (!zbuild_huffman(&z_distance, default_distance,  32)) return 0;
         } else {
            if (!compute_huffman_codes()) return 0;
         }
         if (!parse_huffman_block()) return 0;
      }
   } while (!final);
   return 1;
}

static int do_zlib(char *obuf, int olen, int exp)
{
   zout_start = obuf;
   zout       = obuf;
   zout_end   = obuf + olen;
   z_expandable = exp;

   return parse_zlib();
}

char *stbi_zlib_decode_malloc_guesssize(int initial_size, int *outlen)
{
   char *p = (char *) malloc(initial_size);
   if (p == NULL) return NULL;
   if (do_zlib(p, initial_size, 1)) {
      *outlen = (int) (zout - zout_start);
      return zout_start;
   } else {
      free(zout_start);
      return NULL;
   }
}

char *stbi_zlib_decode_malloc(char *buffer, int len, int *outlen)
{
   zbuffer = (uint8 *) buffer;
   zbuffer_end = (uint8 *) buffer+len;
   return stbi_zlib_decode_malloc_guesssize(16384, outlen);
}

int stbi_zlib_decode_buffer(char *obuffer, int olen, char *ibuffer, int ilen)
{
   zbuffer = (uint8 *) ibuffer;
   zbuffer_end = (uint8 *) ibuffer + ilen;
   if (do_zlib(obuffer, olen, 0))
      return (int) (zout - zout_start);
   else
      return -1;
}
// public domain "baseline" PNG decoder   v0.10  Sean Barrett 2006-11-18
//    simple implementation
//      - only 8-bit samples
//      - no CRC checking
//      - allocates lots of intermediate memory
//        - avoids problem of streaming data between subsystems
//        - avoids explicit window management
//    performance
//      - uses stb_zlib, a PD zlib implementation with fast huffman decoding


typedef struct
{
   unsigned long length;
   unsigned long type;
} chunk;

#define PNG_TYPE(a,b,c,d)  (((a) << 24) + ((b) << 16) + ((c) << 8) + (d))

static chunk get_chunk_header(void)
{
   chunk c;
   c.length = get32();
   c.type   = get32();
   return c;
}

static int check_png_header(void)
{
   static uint8 png_sig[8] = { 137,80,78,71,13,10,26,10 };
   int i;
   for (i=0; i < 8; ++i)
      if (get8() != png_sig[i]) return e("bad png sig","Not a PNG");
   return 1;
}

static uint8 *idata, *expanded, *out;

enum {
   F_none=0, F_sub=1, F_up=2, F_avg=3, F_paeth=4,
   F_avg_first, F_paeth_first,
};

static uint8 first_row_filter[5] =
{
   F_none, F_sub, F_none, F_avg_first, F_paeth_first
};

static int paeth(int a, int b, int c)
{
   int p = a + b - c;
   int pa = abs(p-a);
   int pb = abs(p-b);
   int pc = abs(p-c);
   if (pa <= pb && pa <= pc) return a;
   if (pb <= pc) return b;
   return c;
}

// create the png data from post-deflated data
static int create_png_image(uint8 *raw, uint32 raw_len, int out_n)
{
   uint32 i,j,stride = img_x*out_n;
   int k;
   assert(out_n == img_n || out_n == img_n+1);
   out = (uint8 *) malloc(img_x * img_y * out_n);
   if (!out) return e("outofmem", "Out of memory");
   if (raw_len != (img_n * img_x + 1) * img_y) return e("not enough pixels","Corrupt PNG");
   for (j=0; j < img_y; ++j) {
      uint8 *cur = out + stride*j;
      uint8 *prior = cur - stride;
      int filter = *raw++;
      if (filter > 4) return e("invalid filter","Corrupt PNG");
      // if first row, use special filter that doesn't sample previous row
      if (j == 0) filter = first_row_filter[filter];
      // handle first pixel explicitly
      for (k=0; k < img_n; ++k) {
         switch(filter) {
            case F_none       : cur[k] = raw[k]; break;
            case F_sub        : cur[k] = raw[k]; break;
            case F_up         : cur[k] = raw[k] + prior[k]; break;
            case F_avg        : cur[k] = raw[k] + (prior[k]>>1); break;
            case F_paeth      : cur[k] = (uint8) (raw[k] + paeth(0,prior[k],0)); break;
            case F_avg_first  : cur[k] = raw[k]; break;
            case F_paeth_first: cur[k] = raw[k]; break;
         }
      }
      if (img_n != out_n) cur[img_n] = 255;
      raw += img_n;
      cur += out_n;
      prior += out_n;
      // this is a little gross, so that we don't switch per-pixel or per-component
      if (img_n == out_n) {
         #define CASE(f) \
             case f:     \
                for (i=1; i < img_x; ++i, raw+=img_n,cur+=img_n,prior+=img_n) \
                   for (k=0; k < img_n; ++k)
         switch(filter) {
            CASE(F_none)  cur[k] = raw[k]; break;
            CASE(F_sub)   cur[k] = raw[k] + cur[k-img_n]; break;
            CASE(F_up)    cur[k] = raw[k] + prior[k]; break;
            CASE(F_avg)   cur[k] = raw[k] + ((prior[k] + cur[k-img_n])>>1); break;
            CASE(F_paeth)  cur[k] = (uint8) (raw[k] + paeth(cur[k-img_n],prior[k],prior[k-img_n])); break;
            CASE(F_avg_first)    cur[k] = raw[k] + (cur[k-img_n] >> 1); break;
            CASE(F_paeth_first)  cur[k] = (uint8) (raw[k] + paeth(cur[k-img_n],0,0)); break;
         }
         #undef CASE
      } else {
         assert(img_n+1 == out_n);
         #define CASE(f) \
             case f:     \
                for (i=1; i < img_x; ++i, cur[img_n]=255,raw+=img_n,cur+=out_n,prior+=out_n) \
                   for (k=0; k < img_n; ++k)
         switch(filter) {
            CASE(F_none)  cur[k] = raw[k]; break;
            CASE(F_sub)   cur[k] = raw[k] + cur[k-out_n]; break;
            CASE(F_up)    cur[k] = raw[k] + prior[k]; break;
            CASE(F_avg)   cur[k] = raw[k] + ((prior[k] + cur[k-out_n])>>1); break;
            CASE(F_paeth)  cur[k] = (uint8) (raw[k] + paeth(cur[k-out_n],prior[k],prior[k-out_n])); break;
            CASE(F_avg_first)    cur[k] = raw[k] + (cur[k-out_n] >> 1); break;
            CASE(F_paeth_first)  cur[k] = (uint8) (raw[k] + paeth(cur[k-out_n],0,0)); break;
         }
         #undef CASE
      }
   }
   return 1;
}

static int compute_transparency(uint8 tc[3], int out_n)
{
   uint32 i, pixel_count = img_x * img_y;
   uint8 *p = out;

   // compute color-based transparency, assuming we've
   // already got 255 as the alpha value in the output
   assert(out_n == 2 || out_n == 4);

   p = out;
   if (out_n == 2) {
      for (i=0; i < pixel_count; ++i) {
         p[1] = (p[0] == tc[0] ? 0 : 255);
         p += 2;
      }
   } else {
      for (i=0; i < pixel_count; ++i) {
         if (p[0] == tc[0] && p[1] == tc[1] && p[2] == tc[2])
            p[3] = 0;
         p += 4;
      }
   }
   return 1;
}

static int expand_palette(uint8 *palette, int len, int pal_img_n)
{
   uint32 i, pixel_count = img_x * img_y;
   uint8 *p, *temp_out, *orig = out;

   p = (uint8 *) malloc(pixel_count * pal_img_n);
   if (p == NULL) return e("outofmem", "Out of memory");

   // between here and free(out) below, exitting would leak
   temp_out = p;

   if (pal_img_n == 3) {
      for (i=0; i < pixel_count; ++i) {
         int n = orig[i]*4;
         p[0] = palette[n  ];
         p[1] = palette[n+1];
         p[2] = palette[n+2];
         p += 3;
      }
   } else {
      for (i=0; i < pixel_count; ++i) {
         int n = orig[i]*4;
         p[0] = palette[n  ];
         p[1] = palette[n+1];
         p[2] = palette[n+2];
         p[3] = palette[n+3];
         p += 4;
      }
   }
   free(out);
   out = temp_out;
   return 1;
}

static int parse_png_file(int scan, int req_comp)
{
   uint8 palette[1024], pal_img_n=0;
   uint8 has_trans=0, tc[3];
   uint32 ioff=0, idata_limit=0, i, pal_len=0;
   int first=1,k;

   if (!check_png_header()) return 0;

   if (scan == SCAN_type) return 1;

   for(;;first=0) {
      chunk c = get_chunk_header();
      if (first && c.type != PNG_TYPE('I','H','D','R'))
         return e("first not IHDR","Corrupt PNG");
      switch (c.type) {
         case PNG_TYPE('I','H','D','R'): {
            int depth,color,interlace,comp,filter;
            if (!first) return e("multiple IHDR","Corrupt PNG");
            if (c.length != 13) return e("bad IHDR len","Corrupt PNG");
            img_x = get32(); if (img_x > (1 << 24)) return e("too large","Corrupt PNG");
            img_y = get32(); if (img_y > (1 << 24)) return e("too large","Corrupt PNG");
            depth = get8();  if (depth != 8)        return e("8bit only","PNG not supported: 8-bit only");
            color = get8();  if (color > 6)         return e("bad ctype","Corrupt PNG");
            if (color == 3) pal_img_n = 3; else if (color & 1) return e("bad ctype","Corrupt PNG");
            comp  = get8();  if (comp) return e("bad comp method","Corrupt PNG");
            filter= get8();  if (filter) return e("bad filter method","Corrupt PNG");
            interlace = get8(); if (interlace) return e("interlaced","PNG not supported: interlaced mode");
            if (!img_x || !img_y) return e("0-pixel image","Corrupt PNG");
            if (!pal_img_n) {
               img_n = (color & 2 ? 3 : 1) + (color & 4 ? 1 : 0);
               if ((1 << 30) / img_x / img_n < img_y) return e("too large", "Corrupt PNG");
               if (scan == SCAN_header) return 1;
            } else {
               // if paletted, then pal_n is our final components, and
               // img_n is # components to decompress/filter.
               img_n = 1;
               if ((1 << 30) / img_x / 4 < img_y) return e("too large","Corrupt PNG");
               // if SCAN_header, have to scan to see if we have a tRNS
            }
            break;
         }

         case PNG_TYPE('P','L','T','E'):  {
            if (c.length > 256*3) return e("invalid PLTE","Corrupt PNG");
            pal_len = c.length / 3;
            if (pal_len * 3 != c.length) return e("invalid PLTE","Corrupt PNG");
            for (i=0; i < pal_len; ++i) {
               palette[i*4+0] = get8u();
               palette[i*4+1] = get8u();
               palette[i*4+2] = get8u();
               palette[i*4+3] = 255;
            }
            break;
         }

         case PNG_TYPE('t','R','N','S'): {
            if (idata) return e("tRNS after IDAT","Corrupt PNG");
            if (pal_img_n) {
               if (scan == SCAN_header) { img_n = 4; return 1; }
               if (pal_len == 0) return e("tRNS before PLTE","Corrupt PNG");
               if (c.length > pal_len) return e("bad tRNS len","Corrupt PNG");
               for (i=0; i < c.length; ++i)
                  palette[i*4+3] = get8u();
            } else {
               if (!(img_n & 1)) return e("tRNS with alpha","Corrupt PNG");
               if (c.length != (uint32) img_n*2) return e("bad tRNS len","Corrupt PNG");
               has_trans = 1;
               for (k=0; k < img_n; ++k)
                  tc[k] = (uint8) get16(); // non 8-bit images will be larger
            }
            break;
         }

         case PNG_TYPE('I','D','A','T'): {
            if (pal_img_n && !pal_len) return e("no PLTE","Corrupt PNG");
            if (scan == SCAN_header) { img_n = pal_img_n; return 1; }
            if (ioff + c.length > idata_limit) {
               uint8 *p;
               if (idata_limit == 0) idata_limit = c.length > 4096 ? c.length : 4096;
               while (ioff + c.length > idata_limit)
                  idata_limit *= 2;
               p = (uint8 *) realloc(idata, idata_limit); if (p == NULL) return e("outofmem", "Out of memory");
               idata = p;
            }
            #ifndef STBI_NO_STDIO
            if (img_file)
            {
               if (fread(idata+ioff,1,c.length,img_file) != c.length) return e("outofdata","Corrupt PNG");
            }
            else
            #endif
            {
               memcpy(idata+ioff, img_buffer, c.length);
               img_buffer += c.length;
            }
            ioff += c.length;
            break;
         }

         case PNG_TYPE('I','E','N','D'): {
            uint32 raw_len;
            if (scan != SCAN_load) return 1;
            if (idata == NULL) return e("no IDAT","Corrupt PNG");
            expanded = (uint8 *) stbi_zlib_decode_malloc((char *) idata, ioff, (int *) &raw_len);
            if (expanded == NULL) return 0; // zlib should set error
            free(idata); idata = NULL;
            if ((req_comp == img_n+1 && req_comp != 3 && !pal_img_n) || has_trans)
               img_out_n = img_n+1;
            else
               img_out_n = img_n;
            if (!create_png_image(expanded, raw_len, img_out_n)) return 0;
            if (has_trans)
               if (!compute_transparency(tc, img_out_n)) return 0;
            if (pal_img_n) {
               // pal_img_n == 3 or 4
               img_n = pal_img_n; // record the actual colors we had
               img_out_n = pal_img_n;
               if (req_comp >= 3) img_out_n = req_comp;
               if (!expand_palette(palette, pal_len, img_out_n))
                  return 0;
            }
            free(expanded); expanded = NULL;
            return 1;
         }

         default:
            // if critical, fail
            if ((c.type & (1 << 29)) == 0) {
               #ifndef STBI_NO_FAILURE_STRINGS
               static char invalid_chunk[] = "XXXX chunk not known";
               invalid_chunk[0] = (uint8) (c.type >> 24);
               invalid_chunk[1] = (uint8) (c.type >> 16);
               invalid_chunk[2] = (uint8) (c.type >>  8);
               invalid_chunk[3] = (uint8) (c.type >>  0);
               #endif
               return e(invalid_chunk, "PNG not supported: unknown chunk type");
            }
            skip(c.length);
            break;
      }
      // end of chunk, read and skip CRC
      get8(); get8(); get8(); get8();
   }
}

static unsigned char *do_png(int *x, int *y, int *n, int req_comp)
{
   unsigned char *result=NULL;
   if (req_comp < 0 || req_comp > 4) return ep("bad req_comp", "Internal error");
   if (parse_png_file(SCAN_load, req_comp)) {
      result = out;
      out = NULL;
      if (req_comp && req_comp != img_out_n) {
         result = convert_format(result, img_out_n, req_comp);
         if (result == NULL) return result;
      }
      *x = img_x;
      *y = img_y;
      if (n) *n = img_n;
   }
   free(out);      out      = NULL;
   free(expanded); expanded = NULL;
   free(idata);    idata    = NULL;

   return result;
}

#ifndef STBI_NO_STDIO
unsigned char *stbi_png_load_from_file(FILE *f, int *x, int *y, int *comp, int req_comp)
{
   start_file(f);
   return do_png(x,y,comp,req_comp);
}

unsigned char *stbi_png_load(char *filename, int *x, int *y, int *comp, int req_comp)
{
   unsigned char *data;
   FILE *f = fopen(filename, "rb");
   if (!f) return NULL;
   data = stbi_png_load_from_file(f,x,y,comp,req_comp);
   fclose(f);
   return data;
}
#endif

unsigned char *stbi_png_load_from_memory(unsigned char *buffer, int len, int *x, int *y, int *comp, int req_comp)
{
   start_mem(buffer,len);
   return do_png(x,y,comp,req_comp);
}

#ifndef STBI_NO_STDIO
int stbi_png_test_file(FILE *f)
{
   int n,r;
   n = ftell(f);
   start_file(f);
   r = parse_png_file(SCAN_type,STBI_default);
   fseek(f,n,SEEK_SET);
   return r;
}
#endif

int stbi_png_test_memory(unsigned char *buffer, int len)
{
   start_mem(buffer, len);
   return parse_png_file(SCAN_type,STBI_default);
}

// TODO: load header from png
extern int      stbi_png_info             (char *filename,           int *x, int *y, int *comp);
extern int      stbi_png_info_from_file   (FILE *f,                  int *x, int *y, int *comp);
extern int      stbi_png_info_from_memory (stbi_uc *buffer, int len, int *x, int *y, int *comp);

/////////////////////// write image ///////////////////////

// Microsoft/Windows BMP image

static int bmp_test(void)
{
   int sz;
   if (get8() != 'B') return 0;
   if (get8() != 'M') return 0;
   get32le(); // discard filesize
   get16le(); // discard reserved
   get16le(); // discard reserved
   get32le(); // discard data offset
   sz = get32le();
   if (sz == 12 || sz == 40 || sz == 56 || sz == 108) return 1;
   return 0;
}

#ifndef STBI_NO_STDIO
int      stbi_bmp_test_file        (FILE *f)
{
   int r,n = ftell(f);
   start_file(f);
   r = bmp_test();
   fseek(f,n,SEEK_SET);
   return r;
}
#endif

int      stbi_bmp_test_memory      (stbi_uc *buffer, int len)
{
   start_mem(buffer, len);
   return bmp_test();
}

// returns 0..31 for the highest set bit
static int high_bit(unsigned int z)
{
   int n=0;
   if (z == 0) return -1;
   if (z >= 0x10000) n += 16, z >>= 16;
   if (z >= 0x00100) n +=  8, z >>=  8;
   if (z >= 0x00010) n +=  4, z >>=  4;
   if (z >= 0x00004) n +=  2, z >>=  2;
   if (z >= 0x00002) n +=  1, z >>=  1;
   return n;
}

static int bitcount(unsigned int a)
{
   a = (a & 0x55555555) + ((a >>  1) & 0x55555555); // max 2
   a = (a & 0x33333333) + ((a >>  2) & 0x33333333); // max 4
   a = (a + (a >> 4)) & 0x0f0f0f0f; // max 8 per 4, now 8 bits
   a = (a + (a >> 8)); // max 16 per 8 bits
   a = (a + (a >> 16)); // max 32 per 8 bits
   return a & 0xff;
}

static int shiftsigned(int v, int shift, int bits)
{
   int result;
   int z=0;

   if (shift < 0) v <<= -shift;
   else v >>= shift;
   result = v;

   z = bits;
   while (z < 8) {
      result += v >> z;
      z += bits;
   }
   return result;
}

static stbi_uc *bmp_load(int *x, int *y, int *comp, int req_comp)
{
   unsigned int mr=0,mg=0,mb=0,ma=0;
   stbi_uc pal[256][4];
   int psize=0,i,j,compress=0,width;
   int bpp, flip_vertically, pad, target, offset, hsz;
   if (get8() != 'B' || get8() != 'M') return ep("not BMP", "Corrupt BMP");
   get32le(); // discard filesize
   get16le(); // discard reserved
   get16le(); // discard reserved
   offset = get32le();
   hsz = get32le();
   if (hsz != 12 && hsz != 40 && hsz != 56 && hsz != 108) return ep("unknown BMP", "BMP type not supported: unknown");
   failure_reason = "bad BMP";
   if (hsz == 12) {
      img_x = get16le();
      img_y = get16le();
   } else {
      img_x = get32le();
      img_y = get32le();
   }
   if (get16le() != 1) return 0;
   bpp = get16le();
   if (bpp == 1) return ep("monochrome", "BMP type not supported: 1-bit");
   flip_vertically = img_y > 0;
   img_y = abs(img_y);
   if (hsz == 12) {
      if (bpp < 24)
         psize = (offset - 14 - 24) / 3;
   } else {
      compress = get32le();
      if (compress == 1 || compress == 2) return ep("BMP RLE", "BMP type not supported: RLE");
      get32le(); // discard sizeof
      get32le(); // discard hres
      get32le(); // discard vres
      get32le(); // discard colorsused
      get32le(); // discard max important
      if (hsz == 40 || hsz == 56) {
         if (hsz == 56) {
            get32le();
            get32le();
            get32le();
            get32le();
         }
         if (bpp == 16 || bpp == 32) {
            mr = mg = mb = 0;
            if (compress == 0) {
               if (bpp == 32) {
                  mr = 0xff << 16;
                  mg = 0xff <<  8;
                  mb = 0xff <<  0;
               } else {
                  mr = 31 << 10;
                  mg = 31 <<  5;
                  mb = 31 <<  0;
               }
            } else if (compress == 3) {
               mr = get32le();
               mg = get32le();
               mb = get32le();
               // not documented, but generated by photoshop and handled by mspaint
               if (mr == mg && mg == mb) {
                  // ?!?!?
                  return NULL;
               }
            } else
               return NULL;
         }
      } else {
         assert(hsz == 108);
         mr = get32le();
         mg = get32le();
         mb = get32le();
         ma = get32le();
         get32le(); // discard color space
         for (i=0; i < 12; ++i)
            get32le(); // discard color space parameters
      }
      if (bpp < 16)
         psize = (offset - 14 - hsz) >> 2;
   }
   img_n = ma ? 4 : 3;
   if (req_comp && req_comp >= 3) // we can directly decode 3 or 4
      target = req_comp;
   else
      target = img_n; // if they want monochrome, we'll post-convert
   out = (stbi_uc *) malloc(target * img_x * img_y);
   if (!out) return ep("outofmem", "Out of memory");
   if (bpp < 16) {
      int z=0;
      if (psize == 0 || psize > 256) return ep("invalid", "Corrupt BMP");
      for (i=0; i < psize; ++i) {
         pal[i][2] = get8();
         pal[i][1] = get8();
         pal[i][0] = get8();
         if (hsz != 12) get8();
         pal[i][3] = 255;
      }
      skip(offset - 14 - hsz - psize * (hsz == 12 ? 3 : 4));
      if (bpp == 4) width = (img_x + 1) >> 1;
      else if (bpp == 8) width = img_x;
      else return ep("bad bpp", "Corrupt BMP");
      pad = (-width)&3;
      for (j=0; j < (int) img_y; ++j) {
         for (i=0; i < (int) img_x; i += 2) {
            int v=get8(),v2;
            if (bpp == 4) {
               v2 = v & 15;
               v >>= 4;
            }
            out[z++] = pal[v][0];
            out[z++] = pal[v][1];
            out[z++] = pal[v][2];
            if (target == 4) out[z++] = 255;
            if (i+1 == (int) img_x) break;
            v = (bpp == 8) ? get8() : v2;
            out[z++] = pal[v][0];
            out[z++] = pal[v][1];
            out[z++] = pal[v][2];
            if (target == 4) out[z++] = 255;
         }
         skip(pad);
      }
   } else {
      int rshift,gshift,bshift,ashift,rcount,gcount,bcount,acount;
      int z = 0;
      int easy=0;
      skip(offset - 14 - hsz);
      if (bpp == 24) width = 3 * img_x;
      else if (bpp == 16) width = 2*img_x;
      else /* bpp = 32 and pad = 0 */ width=0;
      pad = (-width) & 3;
      if (bpp == 24) {
         easy = 1;
      } else if (bpp == 32) {
         if (mb == 0xff && mg == 0xff00 && mr == 0xff000000 && ma == 0xff000000)
            easy = 2;
      }
      if (!easy) {
         if (!mr || !mg || !mb) return ep("bad masks", "Corrupt BMP");
         // right shift amt to put high bit in position #7
         rshift = high_bit(mr)-7; rcount = bitcount(mr);
         gshift = high_bit(mg)-7; gcount = bitcount(mr);
         bshift = high_bit(mb)-7; bcount = bitcount(mr);
         ashift = high_bit(ma)-7; acount = bitcount(mr);
      }
      for (j=0; j < (int) img_y; ++j) {
         if (easy) {
            for (i=0; i < (int) img_x; ++i) {
               int a;
               out[z+2] = get8();
               out[z+1] = get8();
               out[z+0] = get8();
               z += 3;
               a = (easy == 2 ? get8() : 255);
               if (target == 4) out[z++] = a;
            }
         } else {
            for (i=0; i < (int) img_x; ++i) {
               unsigned long v = (bpp == 16 ? get16le() : get32le());
               int a;
               out[z++] = shiftsigned(v & mr, rshift, rcount);
               out[z++] = shiftsigned(v & mg, gshift, gcount);
               out[z++] = shiftsigned(v & mb, bshift, bcount);
               a = (ma ? shiftsigned(v & ma, ashift, acount) : 255);
               if (target == 4) out[z++] = a; 
            }
         }
         skip(pad);
      }
   }
   if (flip_vertically) {
      stbi_uc t;
      for (j=0; j < (int) img_y>>1; ++j) {
         stbi_uc *p1 = out +      j     *img_x*target;
         stbi_uc *p2 = out + (img_y-1-j)*img_x*target;
         for (i=0; i < (int) img_x*target; ++i) {
            t = p1[i], p1[i] = p2[i], p2[i] = t;
         }
      }
   }

   if (req_comp && req_comp != target) {
      out = convert_format(out, target, req_comp);
      if (out == NULL) return out; // convert_format frees input on failure
   }

   *x = img_x;
   *y = img_y;
   if (comp) *comp = target;
   return out;
}

#ifndef STBI_NO_STDIO
stbi_uc *stbi_bmp_load             (char *filename,           int *x, int *y, int *comp, int req_comp)
{
   stbi_uc *data;
   FILE *f = fopen(filename, "rb");
   if (!f) return NULL;
   data = bmp_load(x,y,comp,req_comp);
   fclose(f);
   return data;
}

stbi_uc *stbi_bmp_load_from_file   (FILE *f,                  int *x, int *y, int *comp, int req_comp)
{
   start_file(f);
   return bmp_load(x,y,comp,req_comp);
}
#endif

stbi_uc *stbi_bmp_load_from_memory (stbi_uc *buffer, int len, int *x, int *y, int *comp, int req_comp)
{
   start_mem(buffer, len);
   return bmp_load(x,y,comp,req_comp);
}





/////////////////////// write image ///////////////////////

#ifndef STBI_NO_WRITE

static void write8(FILE *f, int x) { uint8 z = (uint8) x; fwrite(&z,1,1,f); }

static void writefv(FILE *f, char *fmt, va_list v)
{
   while (*fmt) {
      switch (*fmt++) {
         case ' ': break;
         case '1': { uint8 x = va_arg(v, int); write8(f,x); break; }
         case '2': { int16 x = va_arg(v, int); write8(f,x); write8(f,x>>8); break; }
         case '4': { int32 x = va_arg(v, int); write8(f,x); write8(f,x>>8); write8(f,x>>16); write8(f,x>>24); break; }
         default:
            assert(0);
            va_end(v);
            return;
      }
   }
}

static void writef(FILE *f, char *fmt, ...)
{
   va_list v;
   va_start(v, fmt);
   writefv(f,fmt,v);
   va_end(v);
}

static void write_pixels(FILE *f, int rgb_dir, int vdir, int x, int y, int comp, void *data, int write_alpha, int scanline_pad)
{
   uint8 bg[3] = { 255, 0, 255}, px[3];
   uint32 zero = 0;
   int i,j,k, j_end;

   if (vdir < 0) 
      j_end = -1, j = y-1;
   else
      j_end =  y, j = 0;

   for (; j != j_end; j += vdir) {
      for (i=0; i < x; ++i) {
         uint8 *d = (uint8 *) data + (j*x+i)*comp;
         if (write_alpha < 0)
            fwrite(&d[comp-1], 1, 1, f);
         switch (comp) {
            case 1:
            case 2: writef(f, "111", d[0],d[0],d[0]);
                    break;
            case 4:
               if (!write_alpha) {
                  for (k=0; k < 3; ++k)
                     px[k] = bg[k] + ((d[k] - bg[k]) * d[3])/255;
                  writef(f, "111", px[1-rgb_dir],px[1],px[1+rgb_dir]);
                  break;
               }
               /* FALLTHROUGH */
            case 3:
               writef(f, "111", d[1-rgb_dir],d[1],d[1+rgb_dir]);
               break;
         }
         if (write_alpha > 0)
            fwrite(&d[comp-1], 1, 1, f);
      }
      fwrite(&zero,scanline_pad,1,f);
   }
}

static int outfile(char *filename, int rgb_dir, int vdir, int x, int y, int comp, void *data, int alpha, int pad, char *fmt, ...)
{
   FILE *f = fopen(filename, "wb");
   if (f) {
      va_list v;
      va_start(v, fmt);
      writefv(f, fmt, v);
      va_end(v);
      write_pixels(f,rgb_dir,vdir,x,y,comp,data,alpha,pad);
      fclose(f);
   }
   return f != NULL;
}

int stbi_write_bmp(char *filename, int x, int y, int comp, void *data)
{
   int pad = (-x*3) & 3;
   return outfile(filename,-1,-1,x,y,comp,data,0,pad,
           "11 4 22 4" "4 44 22 444444",
           'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40,  // file header
            40, x,y, 1,24, 0,0,0,0,0,0);             // bitmap header
}

int stbi_write_tga(char *filename, int x, int y, int comp, void *data)
{
   int has_alpha = !(comp & 1);
   return outfile(filename, -1,-1, x, y, comp, data, has_alpha, 0,
                  "111 221 2222 11", 0,0,2, 0,0,0, 0,0,x,y, 24+8*has_alpha, 8*has_alpha);
}

// any other image formats that do interleaved rgb data?
//    PNG: requires adler32,crc32 -- significant amount of code
//    PSD: no, channels output separately
//    TIFF: no, stripwise-interleaved... i think


#endif