in zlib/deflate.c [379:524]
int ZEXPORT deflateInit2_(z_streamp strm, int level, int method,
int windowBits, int memLevel, int strategy,
const char *version, int stream_size) {
deflate_state *s;
int wrap = 1;
static const char my_version[] = ZLIB_VERSION;
if (version == Z_NULL || version[0] != my_version[0] ||
stream_size != sizeof(z_stream)) {
return Z_VERSION_ERROR;
}
if (strm == Z_NULL) return Z_STREAM_ERROR;
strm->msg = Z_NULL;
if (strm->zalloc == (alloc_func)0) {
#ifdef Z_SOLO
return Z_STREAM_ERROR;
#else
strm->zalloc = zcalloc;
strm->opaque = (voidpf)0;
#endif
}
if (strm->zfree == (free_func)0)
#ifdef Z_SOLO
return Z_STREAM_ERROR;
#else
strm->zfree = zcfree;
#endif
#ifdef FASTEST
if (level != 0) level = 1;
#else
if (level == Z_DEFAULT_COMPRESSION) level = 6;
#endif
if (windowBits < 0) { /* suppress zlib wrapper */
wrap = 0;
if (windowBits < -15)
return Z_STREAM_ERROR;
windowBits = -windowBits;
}
#ifdef GZIP
else if (windowBits > 15) {
wrap = 2; /* write gzip wrapper instead */
windowBits -= 16;
}
#endif
if (memLevel < 1 || memLevel > MAX_MEM_LEVEL || method != Z_DEFLATED ||
windowBits < 8 || windowBits > 15 || level < 0 || level > 9 ||
strategy < 0 || strategy > Z_FIXED || (windowBits == 8 && wrap != 1)) {
return Z_STREAM_ERROR;
}
if (windowBits == 8) windowBits = 9; /* until 256-byte window bug fixed */
s = (deflate_state *) ZALLOC(strm, 1, sizeof(deflate_state));
if (s == Z_NULL) return Z_MEM_ERROR;
strm->state = (struct internal_state FAR *)s;
s->strm = strm;
s->status = INIT_STATE; /* to pass state test in deflateReset() */
s->wrap = wrap;
s->gzhead = Z_NULL;
s->w_bits = (uInt)windowBits;
s->w_size = 1 << s->w_bits;
s->w_mask = s->w_size - 1;
s->hash_bits = (uInt)memLevel + 7;
s->hash_size = 1 << s->hash_bits;
s->hash_mask = s->hash_size - 1;
s->hash_shift = ((s->hash_bits + MIN_MATCH-1) / MIN_MATCH);
s->window = (Bytef *) ZALLOC(strm, s->w_size, 2*sizeof(Byte));
s->prev = (Posf *) ZALLOC(strm, s->w_size, sizeof(Pos));
s->head = (Posf *) ZALLOC(strm, s->hash_size, sizeof(Pos));
s->high_water = 0; /* nothing written to s->window yet */
s->lit_bufsize = 1 << (memLevel + 6); /* 16K elements by default */
/* We overlay pending_buf and sym_buf. This works since the average size
* for length/distance pairs over any compressed block is assured to be 31
* bits or less.
*
* Analysis: The longest fixed codes are a length code of 8 bits plus 5
* extra bits, for lengths 131 to 257. The longest fixed distance codes are
* 5 bits plus 13 extra bits, for distances 16385 to 32768. The longest
* possible fixed-codes length/distance pair is then 31 bits total.
*
* sym_buf starts one-fourth of the way into pending_buf. So there are
* three bytes in sym_buf for every four bytes in pending_buf. Each symbol
* in sym_buf is three bytes -- two for the distance and one for the
* literal/length. As each symbol is consumed, the pointer to the next
* sym_buf value to read moves forward three bytes. From that symbol, up to
* 31 bits are written to pending_buf. The closest the written pending_buf
* bits gets to the next sym_buf symbol to read is just before the last
* code is written. At that time, 31*(n - 2) bits have been written, just
* after 24*(n - 2) bits have been consumed from sym_buf. sym_buf starts at
* 8*n bits into pending_buf. (Note that the symbol buffer fills when n - 1
* symbols are written.) The closest the writing gets to what is unread is
* then n + 14 bits. Here n is lit_bufsize, which is 16384 by default, and
* can range from 128 to 32768.
*
* Therefore, at a minimum, there are 142 bits of space between what is
* written and what is read in the overlain buffers, so the symbols cannot
* be overwritten by the compressed data. That space is actually 139 bits,
* due to the three-bit fixed-code block header.
*
* That covers the case where either Z_FIXED is specified, forcing fixed
* codes, or when the use of fixed codes is chosen, because that choice
* results in a smaller compressed block than dynamic codes. That latter
* condition then assures that the above analysis also covers all dynamic
* blocks. A dynamic-code block will only be chosen to be emitted if it has
* fewer bits than a fixed-code block would for the same set of symbols.
* Therefore its average symbol length is assured to be less than 31. So
* the compressed data for a dynamic block also cannot overwrite the
* symbols from which it is being constructed.
*/
s->pending_buf = (uchf *) ZALLOC(strm, s->lit_bufsize, LIT_BUFS);
s->pending_buf_size = (ulg)s->lit_bufsize * 4;
if (s->window == Z_NULL || s->prev == Z_NULL || s->head == Z_NULL ||
s->pending_buf == Z_NULL) {
s->status = FINISH_STATE;
strm->msg = ERR_MSG(Z_MEM_ERROR);
deflateEnd (strm);
return Z_MEM_ERROR;
}
#ifdef LIT_MEM
s->d_buf = (ushf *)(s->pending_buf + (s->lit_bufsize << 1));
s->l_buf = s->pending_buf + (s->lit_bufsize << 2);
s->sym_end = s->lit_bufsize - 1;
#else
s->sym_buf = s->pending_buf + s->lit_bufsize;
s->sym_end = (s->lit_bufsize - 1) * 3;
#endif
/* We avoid equality with lit_bufsize*3 because of wraparound at 64K
* on 16 bit machines and because stored blocks are restricted to
* 64K-1 bytes.
*/
s->level = level;
s->strategy = strategy;
s->method = (Byte)method;
return deflateReset(strm);
}