stb-imv/stb_image.c

/* stbi-0.93 - public domain JPEG/PNG reader - http://nothings.org/stb_image.c
                      when you control the images you're loading
  
   TODO:
      stbi_info_*
  
   history:
      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) -- image height must be in header
//    - unsophisticated error handling
//
// 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 STB_IMAGE_NO_FAILURE_REASON to avoid
// compiling these strings at all.
//
// Paletted PNG images are automatically depalettized.

#include <stdio.h>

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
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);
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 STB_IMAGE_NO_FAILURE_STRINGS
   #define e(x,y)  0
#elif defined(STB_IMAGE_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);
}

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");
}

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.
static FILE  *img_file;
static uint8 *img_buffer, *img_buffer_end;

static void start_file(FILE *f)
{
   img_file = f;
}

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

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

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

static void skip(int n)
{
   if (img_file)
      fseek(img_file, n, SEEK_CUR);
   else
      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)
{
   if (img_file)
      fread(buffer, 1, n, img_file);
   else {
      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();
   }
   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;
   }
}

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;
}

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);
}

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;
}

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;
            }
            if (img_file) {
               if (fread(idata+ioff,1,c.length,img_file) != c.length) return e("outofdata","Corrupt PNG");
            } else {
               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 STB_IMAGE_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;
}

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;
}

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);
}

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;
}

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 == 108) return 1;
   return 0;
}

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;
}

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 != 108) return ep("unknown BMP", "BMP type not supported: unknown");
   failure_reason = "bad BMP";
   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 = get32();
      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) {
         if (bpp == 16 || bpp == 32) {
            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();
            } 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;
}

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);
}

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