acd6fdee98
the differences between the "zlib format" used by SQLAR, the raw deflate format used by ZIP, and the custom format used by compress.c. No changes to code. FossilOrigin-Name: c13415c5caf06eaa73086c500907451dfcdfd1354ac4a9ab63edb7255edbfa1b
130 lines
3.7 KiB
C
130 lines
3.7 KiB
C
/*
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** 2014-06-13
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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******************************************************************************
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**
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** This SQLite extension implements SQL compression functions
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** compress() and uncompress() using ZLIB.
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*/
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#include "sqlite3ext.h"
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SQLITE_EXTENSION_INIT1
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#include <zlib.h>
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/*
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** Implementation of the "compress(X)" SQL function. The input X is
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** compressed using zLib and the output is returned.
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**
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** The output is a BLOB that begins with a variable-length integer that
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** is the input size in bytes (the size of X before compression). The
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** variable-length integer is implemented as 1 to 5 bytes. There are
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** seven bits per integer stored in the lower seven bits of each byte.
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** More significant bits occur first. The most significant bit (0x80)
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** is a flag to indicate the end of the integer.
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**
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** This function, SQLAR, and ZIP all use the same "deflate" compression
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** algorithm, but each is subtly different:
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**
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** * ZIP uses raw deflate.
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**
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** * SQLAR uses the "zlib format" which is raw deflate with a two-byte
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** algorithm-identification header and a four-byte checksum at the end.
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**
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** * This utility uses the "zlib format" like SQLAR, but adds the variable-
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** length integer uncompressed size value at the beginning.
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**
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** This function might be extended in the future to support compression
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** formats other than deflate, by providing a different algorithm-id
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** mark following the variable-length integer size parameter.
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*/
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static void compressFunc(
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sqlite3_context *context,
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int argc,
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sqlite3_value **argv
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){
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const unsigned char *pIn;
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unsigned char *pOut;
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unsigned int nIn;
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unsigned long int nOut;
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unsigned char x[8];
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int rc;
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int i, j;
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pIn = sqlite3_value_blob(argv[0]);
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nIn = sqlite3_value_bytes(argv[0]);
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nOut = 13 + nIn + (nIn+999)/1000;
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pOut = sqlite3_malloc( nOut+5 );
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for(i=4; i>=0; i--){
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x[i] = (nIn >> (7*(4-i)))&0x7f;
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}
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for(i=0; i<4 && x[i]==0; i++){}
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for(j=0; i<=4; i++, j++) pOut[j] = x[i];
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pOut[j-1] |= 0x80;
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rc = compress(&pOut[j], &nOut, pIn, nIn);
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if( rc==Z_OK ){
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sqlite3_result_blob(context, pOut, nOut+j, sqlite3_free);
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}else{
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sqlite3_free(pOut);
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}
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}
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/*
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** Implementation of the "uncompress(X)" SQL function. The argument X
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** is a blob which was obtained from compress(Y). The output will be
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** the value Y.
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*/
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static void uncompressFunc(
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sqlite3_context *context,
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int argc,
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sqlite3_value **argv
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){
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const unsigned char *pIn;
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unsigned char *pOut;
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unsigned int nIn;
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unsigned long int nOut;
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int rc;
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int i;
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pIn = sqlite3_value_blob(argv[0]);
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nIn = sqlite3_value_bytes(argv[0]);
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nOut = 0;
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for(i=0; i<nIn && i<5; i++){
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nOut = (nOut<<7) | (pIn[i]&0x7f);
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if( (pIn[i]&0x80)!=0 ){ i++; break; }
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}
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pOut = sqlite3_malloc( nOut+1 );
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rc = uncompress(pOut, &nOut, &pIn[i], nIn-i);
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if( rc==Z_OK ){
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sqlite3_result_blob(context, pOut, nOut, sqlite3_free);
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}else{
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sqlite3_free(pOut);
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}
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}
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#ifdef _WIN32
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__declspec(dllexport)
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#endif
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int sqlite3_compress_init(
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sqlite3 *db,
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char **pzErrMsg,
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const sqlite3_api_routines *pApi
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){
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int rc = SQLITE_OK;
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SQLITE_EXTENSION_INIT2(pApi);
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(void)pzErrMsg; /* Unused parameter */
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rc = sqlite3_create_function(db, "compress", 1, SQLITE_UTF8, 0,
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compressFunc, 0, 0);
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if( rc==SQLITE_OK ){
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rc = sqlite3_create_function(db, "uncompress", 1, SQLITE_UTF8, 0,
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uncompressFunc, 0, 0);
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}
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return rc;
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}
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