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deflate.c
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deflate.c
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/*
* Reimplementation of Deflate (RFC1951) compression. Adapted from
* the version in PuTTY, and extended to write dynamic Huffman
* trees and choose block boundaries usefully.
*/
/*
* TODO:
*
* - Feature: could do with forms of flush other than SYNC_FLUSH.
* I'm not sure exactly how those work when you don't know in
* advance that your next block will be static (as we did in
* PuTTY). And remember the 9-bit limitation of zlib.
* + also, zlib has FULL_FLUSH which clears the LZ77 state as
* well, for random access.
*
* - Compression quality: chooseblock() appears to be computing
* wildly inaccurate block size estimates. Possible resolutions:
* + find and fix some trivial bug I haven't spotted yet
* + abandon the entropic approximation and go with trial
* Huffman runs
*
* - Compression quality: see if increasing SYMLIMIT causes
* dynamic blocks to start being consistently smaller than it.
* + actually we seem to be there already, but check on a
* larger corpus.
*
* - Compression quality: we ought to be able to fall right back
* to actual uncompressed blocks if really necessary, though
* it's not clear what the criterion for doing so would be.
*/
/*
* This software is copyright 2000-2006 Simon Tatham.
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
* IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include <stdio.h>
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include "halibut.h"
#include "huffman.h"
#include "lz77.h"
#include "deflate.h"
/* ----------------------------------------------------------------------
* This file can be compiled in a number of modes.
*
* With -DSTANDALONE, it builds a self-contained deflate tool which
* can compress, decompress, and also analyse a deflated file to
* print out the sequence of literals and copy commands it
* contains.
*
* With -DTESTMODE, it builds a test application which is given a
* file on standard input, both compresses and decompresses it, and
* outputs the re-decompressed result so it can be conveniently
* diffed against the original. Define -DTESTDBG as well for lots
* of diagnostics.
*/
#if defined TESTDBG
/* gcc-specific diagnostic macro */
#define debug_int(x...) ( fprintf(stderr, x) )
#define debug(x) ( debug_int x )
#else
#define debug(x) ((void)0)
#endif
#ifdef STANDALONE
#define ANALYSIS
#endif
#ifdef ANALYSIS
int analyse_level = 0;
#endif
/* ----------------------------------------------------------------------
* Deflate functionality common to both compression and decompression.
*/
#define DWINSIZE 32768
static const unsigned char lenlenmap[] = {
16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
};
/*
* Given a sequence of Huffman code lengths, compute the actual codes
* in the final form suitable for feeding to outbits (i.e. already
* bit-mirrored). Returns the same as compute_huffman_codes.
*/
static int deflate_hufcodes(const unsigned char *lengths,
int *codes, int nsyms)
{
int maxlen = compute_huffman_codes(lengths, codes, nsyms);
int i, j;
for (i = 0; i < nsyms; i++) {
int code = codes[i];
codes[i] = 0;
for (j = 0; j < lengths[i]; j++) {
codes[i] = (codes[i] << 1) | (code & 1);
code >>= 1;
}
}
return maxlen;
}
/*
* Adler32 checksum function.
*/
static unsigned long adler32_update(unsigned long s,
const unsigned char *data, int len)
{
unsigned s1 = s & 0xFFFF, s2 = (s >> 16) & 0xFFFF;
int i;
for (i = 0; i < len; i++) {
s1 += data[i];
s2 += s1;
if (!(i & 0xFFF)) {
s1 %= 65521;
s2 %= 65521;
}
}
return ((s2 % 65521) << 16) | (s1 % 65521);
}
/*
* CRC32 checksum function.
*/
static unsigned long crc32_update(unsigned long crcword,
const unsigned char *data, int len)
{
static const unsigned long crc32_table[256] = {
0x00000000L, 0x77073096L, 0xEE0E612CL, 0x990951BAL,
0x076DC419L, 0x706AF48FL, 0xE963A535L, 0x9E6495A3L,
0x0EDB8832L, 0x79DCB8A4L, 0xE0D5E91EL, 0x97D2D988L,
0x09B64C2BL, 0x7EB17CBDL, 0xE7B82D07L, 0x90BF1D91L,
0x1DB71064L, 0x6AB020F2L, 0xF3B97148L, 0x84BE41DEL,
0x1ADAD47DL, 0x6DDDE4EBL, 0xF4D4B551L, 0x83D385C7L,
0x136C9856L, 0x646BA8C0L, 0xFD62F97AL, 0x8A65C9ECL,
0x14015C4FL, 0x63066CD9L, 0xFA0F3D63L, 0x8D080DF5L,
0x3B6E20C8L, 0x4C69105EL, 0xD56041E4L, 0xA2677172L,
0x3C03E4D1L, 0x4B04D447L, 0xD20D85FDL, 0xA50AB56BL,
0x35B5A8FAL, 0x42B2986CL, 0xDBBBC9D6L, 0xACBCF940L,
0x32D86CE3L, 0x45DF5C75L, 0xDCD60DCFL, 0xABD13D59L,
0x26D930ACL, 0x51DE003AL, 0xC8D75180L, 0xBFD06116L,
0x21B4F4B5L, 0x56B3C423L, 0xCFBA9599L, 0xB8BDA50FL,
0x2802B89EL, 0x5F058808L, 0xC60CD9B2L, 0xB10BE924L,
0x2F6F7C87L, 0x58684C11L, 0xC1611DABL, 0xB6662D3DL,
0x76DC4190L, 0x01DB7106L, 0x98D220BCL, 0xEFD5102AL,
0x71B18589L, 0x06B6B51FL, 0x9FBFE4A5L, 0xE8B8D433L,
0x7807C9A2L, 0x0F00F934L, 0x9609A88EL, 0xE10E9818L,
0x7F6A0DBBL, 0x086D3D2DL, 0x91646C97L, 0xE6635C01L,
0x6B6B51F4L, 0x1C6C6162L, 0x856530D8L, 0xF262004EL,
0x6C0695EDL, 0x1B01A57BL, 0x8208F4C1L, 0xF50FC457L,
0x65B0D9C6L, 0x12B7E950L, 0x8BBEB8EAL, 0xFCB9887CL,
0x62DD1DDFL, 0x15DA2D49L, 0x8CD37CF3L, 0xFBD44C65L,
0x4DB26158L, 0x3AB551CEL, 0xA3BC0074L, 0xD4BB30E2L,
0x4ADFA541L, 0x3DD895D7L, 0xA4D1C46DL, 0xD3D6F4FBL,
0x4369E96AL, 0x346ED9FCL, 0xAD678846L, 0xDA60B8D0L,
0x44042D73L, 0x33031DE5L, 0xAA0A4C5FL, 0xDD0D7CC9L,
0x5005713CL, 0x270241AAL, 0xBE0B1010L, 0xC90C2086L,
0x5768B525L, 0x206F85B3L, 0xB966D409L, 0xCE61E49FL,
0x5EDEF90EL, 0x29D9C998L, 0xB0D09822L, 0xC7D7A8B4L,
0x59B33D17L, 0x2EB40D81L, 0xB7BD5C3BL, 0xC0BA6CADL,
0xEDB88320L, 0x9ABFB3B6L, 0x03B6E20CL, 0x74B1D29AL,
0xEAD54739L, 0x9DD277AFL, 0x04DB2615L, 0x73DC1683L,
0xE3630B12L, 0x94643B84L, 0x0D6D6A3EL, 0x7A6A5AA8L,
0xE40ECF0BL, 0x9309FF9DL, 0x0A00AE27L, 0x7D079EB1L,
0xF00F9344L, 0x8708A3D2L, 0x1E01F268L, 0x6906C2FEL,
0xF762575DL, 0x806567CBL, 0x196C3671L, 0x6E6B06E7L,
0xFED41B76L, 0x89D32BE0L, 0x10DA7A5AL, 0x67DD4ACCL,
0xF9B9DF6FL, 0x8EBEEFF9L, 0x17B7BE43L, 0x60B08ED5L,
0xD6D6A3E8L, 0xA1D1937EL, 0x38D8C2C4L, 0x4FDFF252L,
0xD1BB67F1L, 0xA6BC5767L, 0x3FB506DDL, 0x48B2364BL,
0xD80D2BDAL, 0xAF0A1B4CL, 0x36034AF6L, 0x41047A60L,
0xDF60EFC3L, 0xA867DF55L, 0x316E8EEFL, 0x4669BE79L,
0xCB61B38CL, 0xBC66831AL, 0x256FD2A0L, 0x5268E236L,
0xCC0C7795L, 0xBB0B4703L, 0x220216B9L, 0x5505262FL,
0xC5BA3BBEL, 0xB2BD0B28L, 0x2BB45A92L, 0x5CB36A04L,
0xC2D7FFA7L, 0xB5D0CF31L, 0x2CD99E8BL, 0x5BDEAE1DL,
0x9B64C2B0L, 0xEC63F226L, 0x756AA39CL, 0x026D930AL,
0x9C0906A9L, 0xEB0E363FL, 0x72076785L, 0x05005713L,
0x95BF4A82L, 0xE2B87A14L, 0x7BB12BAEL, 0x0CB61B38L,
0x92D28E9BL, 0xE5D5BE0DL, 0x7CDCEFB7L, 0x0BDBDF21L,
0x86D3D2D4L, 0xF1D4E242L, 0x68DDB3F8L, 0x1FDA836EL,
0x81BE16CDL, 0xF6B9265BL, 0x6FB077E1L, 0x18B74777L,
0x88085AE6L, 0xFF0F6A70L, 0x66063BCAL, 0x11010B5CL,
0x8F659EFFL, 0xF862AE69L, 0x616BFFD3L, 0x166CCF45L,
0xA00AE278L, 0xD70DD2EEL, 0x4E048354L, 0x3903B3C2L,
0xA7672661L, 0xD06016F7L, 0x4969474DL, 0x3E6E77DBL,
0xAED16A4AL, 0xD9D65ADCL, 0x40DF0B66L, 0x37D83BF0L,
0xA9BCAE53L, 0xDEBB9EC5L, 0x47B2CF7FL, 0x30B5FFE9L,
0xBDBDF21CL, 0xCABAC28AL, 0x53B39330L, 0x24B4A3A6L,
0xBAD03605L, 0xCDD70693L, 0x54DE5729L, 0x23D967BFL,
0xB3667A2EL, 0xC4614AB8L, 0x5D681B02L, 0x2A6F2B94L,
0xB40BBE37L, 0xC30C8EA1L, 0x5A05DF1BL, 0x2D02EF8DL
};
crcword ^= 0xFFFFFFFFL;
while (len--) {
unsigned long newbyte = *data++;
newbyte ^= crcword & 0xFFL;
crcword = (crcword >> 8) ^ crc32_table[newbyte];
}
return crcword ^ 0xFFFFFFFFL;
}
typedef struct {
short code, extrabits;
int min, max;
} coderecord;
static const coderecord lencodes[] = {
{257, 0, 3, 3},
{258, 0, 4, 4},
{259, 0, 5, 5},
{260, 0, 6, 6},
{261, 0, 7, 7},
{262, 0, 8, 8},
{263, 0, 9, 9},
{264, 0, 10, 10},
{265, 1, 11, 12},
{266, 1, 13, 14},
{267, 1, 15, 16},
{268, 1, 17, 18},
{269, 2, 19, 22},
{270, 2, 23, 26},
{271, 2, 27, 30},
{272, 2, 31, 34},
{273, 3, 35, 42},
{274, 3, 43, 50},
{275, 3, 51, 58},
{276, 3, 59, 66},
{277, 4, 67, 82},
{278, 4, 83, 98},
{279, 4, 99, 114},
{280, 4, 115, 130},
{281, 5, 131, 162},
{282, 5, 163, 194},
{283, 5, 195, 226},
{284, 5, 227, 257},
{285, 0, 258, 258},
};
static const coderecord distcodes[] = {
{0, 0, 1, 1},
{1, 0, 2, 2},
{2, 0, 3, 3},
{3, 0, 4, 4},
{4, 1, 5, 6},
{5, 1, 7, 8},
{6, 2, 9, 12},
{7, 2, 13, 16},
{8, 3, 17, 24},
{9, 3, 25, 32},
{10, 4, 33, 48},
{11, 4, 49, 64},
{12, 5, 65, 96},
{13, 5, 97, 128},
{14, 6, 129, 192},
{15, 6, 193, 256},
{16, 7, 257, 384},
{17, 7, 385, 512},
{18, 8, 513, 768},
{19, 8, 769, 1024},
{20, 9, 1025, 1536},
{21, 9, 1537, 2048},
{22, 10, 2049, 3072},
{23, 10, 3073, 4096},
{24, 11, 4097, 6144},
{25, 11, 6145, 8192},
{26, 12, 8193, 12288},
{27, 12, 12289, 16384},
{28, 13, 16385, 24576},
{29, 13, 24577, 32768},
};
/* ----------------------------------------------------------------------
* Deflate compression.
*/
#define SYMLIMIT 65536
#define SYMPFX_LITLEN 0x00000000U
#define SYMPFX_DIST 0x40000000U
#define SYMPFX_EXTRABITS 0x80000000U
#define SYMPFX_CODELEN 0xC0000000U
#define SYMPFX_MASK 0xC0000000U
#define SYM_EXTRABITS_MASK 0x3C000000U
#define SYM_EXTRABITS_SHIFT 26
struct huftrees {
unsigned char *len_litlen;
int *code_litlen;
unsigned char *len_dist;
int *code_dist;
unsigned char *len_codelen;
int *code_codelen;
};
struct deflate_compress_ctx {
struct LZ77Context *lzc;
unsigned char *outbuf;
int outlen, outsize;
unsigned long outbits;
int noutbits;
bool firstblock;
unsigned long *syms;
int symstart, nsyms;
int type;
unsigned long checksum;
unsigned long datasize;
bool lastblock;
bool finished;
unsigned char static_len1[288], static_len2[30];
int static_code1[288], static_code2[30];
struct huftrees sht;
#ifdef STATISTICS
unsigned long bitcount;
#endif
};
static void outbits(deflate_compress_ctx *out,
unsigned long bits, int nbits)
{
assert(out->noutbits + nbits <= 32);
out->outbits |= bits << out->noutbits;
out->noutbits += nbits;
while (out->noutbits >= 8) {
if (out->outlen >= out->outsize) {
out->outsize = out->outlen + 64;
out->outbuf = sresize(out->outbuf, out->outsize, unsigned char);
}
out->outbuf[out->outlen++] = (unsigned char) (out->outbits & 0xFF);
out->outbits >>= 8;
out->noutbits -= 8;
}
#ifdef STATISTICS
out->bitcount += nbits;
#endif
}
/*
* Compute the bit length of a symbol, given the three Huffman
* trees.
*/
static int symsize(unsigned sym, const struct huftrees *trees)
{
unsigned basesym = sym &~ SYMPFX_MASK;
switch (sym & SYMPFX_MASK) {
case SYMPFX_LITLEN:
return trees->len_litlen[basesym];
case SYMPFX_DIST:
return trees->len_dist[basesym];
case SYMPFX_CODELEN:
return trees->len_codelen[basesym];
default /*case SYMPFX_EXTRABITS*/:
return basesym >> SYM_EXTRABITS_SHIFT;
}
}
/*
* Write out a single symbol, given the three Huffman trees.
*/
static void writesym(deflate_compress_ctx *out,
unsigned sym, const struct huftrees *trees)
{
unsigned basesym = sym &~ SYMPFX_MASK;
int i;
switch (sym & SYMPFX_MASK) {
case SYMPFX_LITLEN:
debug(("send: litlen %d\n", basesym));
outbits(out, trees->code_litlen[basesym], trees->len_litlen[basesym]);
break;
case SYMPFX_DIST:
debug(("send: dist %d\n", basesym));
outbits(out, trees->code_dist[basesym], trees->len_dist[basesym]);
break;
case SYMPFX_CODELEN:
debug(("send: codelen %d\n", basesym));
outbits(out, trees->code_codelen[basesym],trees->len_codelen[basesym]);
break;
case SYMPFX_EXTRABITS:
i = basesym >> SYM_EXTRABITS_SHIFT;
basesym &= ~SYM_EXTRABITS_MASK;
debug(("send: extrabits %d/%d\n", basesym, i));
outbits(out, basesym, i);
break;
}
}
/*
* outblock() must output _either_ a dynamic block of length
* `dynamic_len', _or_ a static block of length `static_len', but
* it gets to choose which.
*/
static void outblock(deflate_compress_ctx *out,
int dynamic_len, int static_len)
{
int freqs1[286], freqs2[30], freqs3[19];
unsigned char len1[286], len2[30], len3[19];
int code1[286], code2[30], code3[19];
int hlit, hdist, hclen, bfinal, btype;
int treesrc[286 + 30];
int treesyms[286 + 30];
int codelen[19];
int i, ntreesrc, ntreesyms;
bool dynamic;
int blklen;
struct huftrees dht;
const struct huftrees *ht;
#ifdef STATISTICS
unsigned long bitcount_before;
#endif
dht.len_litlen = len1;
dht.len_dist = len2;
dht.len_codelen = len3;
dht.code_litlen = code1;
dht.code_dist = code2;
dht.code_codelen = code3;
/*
* We make our choice of block to output by doing all the
* detailed work to determine the exact length of each possible
* block. Then we choose the one which has fewest output bits
* per symbol.
*/
/*
* First build the two main Huffman trees for the dynamic
* block.
*/
/*
* Count up the frequency tables.
*/
memset(freqs1, 0, sizeof(freqs1));
memset(freqs2, 0, sizeof(freqs2));
freqs1[256] = 1; /* we're bound to need one EOB */
for (i = 0; i < dynamic_len; i++) {
unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
/*
* Increment the occurrence counter for this symbol, if
* it's in one of the Huffman alphabets and isn't extra
* bits.
*/
if ((sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
sym &= ~SYMPFX_MASK;
assert(sym < lenof(freqs1));
freqs1[sym]++;
} else if ((sym & SYMPFX_MASK) == SYMPFX_DIST) {
sym &= ~SYMPFX_MASK;
assert(sym < lenof(freqs2));
freqs2[sym]++;
}
}
build_huffman_tree(freqs1, len1, lenof(freqs1), 15);
build_huffman_tree(freqs2, len2, lenof(freqs2), 15);
deflate_hufcodes(len1, code1, lenof(freqs1));
deflate_hufcodes(len2, code2, lenof(freqs2));
/*
* Determine HLIT and HDIST.
*/
for (hlit = 286; hlit > 257 && len1[hlit-1] == 0; hlit--);
for (hdist = 30; hdist > 1 && len2[hdist-1] == 0; hdist--);
/*
* Write out the list of symbols used to transmit the
* trees.
*/
ntreesrc = 0;
for (i = 0; i < hlit; i++)
treesrc[ntreesrc++] = len1[i];
for (i = 0; i < hdist; i++)
treesrc[ntreesrc++] = len2[i];
ntreesyms = 0;
for (i = 0; i < ntreesrc ;) {
int j = 1;
int k;
/* Find length of run of the same length code. */
while (i+j < ntreesrc && treesrc[i+j] == treesrc[i])
j++;
/* Encode that run as economically as we can. */
k = j;
if (treesrc[i] == 0) {
/*
* Zero code length: we can output run codes for
* 3-138 zeroes. So if we have fewer than 3 zeroes,
* we just output literals. Otherwise, we output
* nothing but run codes, and tweak their lengths
* to make sure we aren't left with under 3 at the
* end.
*/
if (k < 3) {
while (k--)
treesyms[ntreesyms++] = 0 | SYMPFX_CODELEN;
} else {
while (k > 0) {
int rpt = (k < 138 ? k : 138);
if (rpt > k-3 && rpt < k)
rpt = k-3;
assert(rpt >= 3 && rpt <= 138);
if (rpt < 11) {
treesyms[ntreesyms++] = 17 | SYMPFX_CODELEN;
treesyms[ntreesyms++] =
(SYMPFX_EXTRABITS | (rpt - 3) |
(3 << SYM_EXTRABITS_SHIFT));
} else {
treesyms[ntreesyms++] = 18 | SYMPFX_CODELEN;
treesyms[ntreesyms++] =
(SYMPFX_EXTRABITS | (rpt - 11) |
(7 << SYM_EXTRABITS_SHIFT));
}
k -= rpt;
}
}
} else {
/*
* Non-zero code length: we must output the first
* one explicitly, then we can output a copy code
* for 3-6 repeats. So if we have fewer than 4
* repeats, we _just_ output literals. Otherwise,
* we output one literal plus at least one copy
* code, and tweak the copy codes to make sure we
* aren't left with under 3 at the end.
*/
assert(treesrc[i] < 16);
treesyms[ntreesyms++] = treesrc[i] | SYMPFX_CODELEN;
k--;
if (k < 3) {
while (k--)
treesyms[ntreesyms++] = treesrc[i] | SYMPFX_CODELEN;
} else {
while (k > 0) {
int rpt = (k < 6 ? k : 6);
if (rpt > k-3 && rpt < k)
rpt = k-3;
assert(rpt >= 3 && rpt <= 6);
treesyms[ntreesyms++] = 16 | SYMPFX_CODELEN;
treesyms[ntreesyms++] = (SYMPFX_EXTRABITS | (rpt - 3) |
(2 << SYM_EXTRABITS_SHIFT));
k -= rpt;
}
}
}
i += j;
}
assert((unsigned)ntreesyms < lenof(treesyms));
/*
* Count up the frequency table for the tree-transmission
* symbols, and build the auxiliary Huffman tree for that.
*/
memset(freqs3, 0, sizeof(freqs3));
for (i = 0; i < ntreesyms; i++) {
unsigned sym = treesyms[i];
/*
* Increment the occurrence counter for this symbol, if
* it's the Huffman alphabet and isn't extra bits.
*/
if ((sym & SYMPFX_MASK) == SYMPFX_CODELEN) {
sym &= ~SYMPFX_MASK;
assert(sym < lenof(freqs3));
freqs3[sym]++;
}
}
build_huffman_tree(freqs3, len3, lenof(freqs3), 7);
deflate_hufcodes(len3, code3, lenof(freqs3));
/*
* Reorder the code length codes into transmission order, and
* determine HCLEN.
*/
for (i = 0; i < 19; i++)
codelen[i] = len3[lenlenmap[i]];
for (hclen = 19; hclen > 4 && codelen[hclen-1] == 0; hclen--)
/* empty loop body */;
/*
* Now work out the exact size of both the dynamic and the
* static block, in bits.
*/
{
int ssize, dsize;
/*
* First the dynamic block.
*/
dsize = 3 + 5 + 5 + 4; /* 3-bit header, HLIT, HDIST, HCLEN */
dsize += 3 * hclen; /* code-length-alphabet code lengths */
/* Code lengths */
for (i = 0; i < ntreesyms; i++)
dsize += symsize(treesyms[i], &dht);
/* The actual block data */
for (i = 0; i < dynamic_len; i++) {
unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
dsize += symsize(sym, &dht);
}
/* And the end-of-data symbol. */
dsize += symsize(SYMPFX_LITLEN | 256, &dht);
/*
* Now the static block.
*/
ssize = 3; /* 3-bit block header */
/* The actual block data */
for (i = 0; i < static_len; i++) {
unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
ssize += symsize(sym, &out->sht);
}
/* And the end-of-data symbol. */
ssize += symsize(SYMPFX_LITLEN | 256, &out->sht);
/*
* Compare the two and decide which to output. We break
* exact ties in favour of the static block, because of the
* special case in which that block has zero length.
*/
dynamic = ((double)ssize * dynamic_len > (double)dsize * static_len);
ht = dynamic ? &dht : &out->sht;
blklen = dynamic ? dynamic_len : static_len;
}
/*
* Actually transmit the block.
*/
/* 3-bit block header */
bfinal = (out->lastblock ? 1 : 0);
btype = dynamic ? 2 : 1;
debug(("send: bfinal=%d btype=%d\n", bfinal, btype));
outbits(out, bfinal, 1);
outbits(out, btype, 2);
#ifdef STATISTICS
bitcount_before = out->bitcount;
#endif
if (dynamic) {
/* HLIT, HDIST and HCLEN */
debug(("send: hlit=%d hdist=%d hclen=%d\n", hlit, hdist, hclen));
outbits(out, hlit - 257, 5);
outbits(out, hdist - 1, 5);
outbits(out, hclen - 4, 4);
/* Code lengths for the auxiliary tree */
for (i = 0; i < hclen; i++) {
debug(("send: lenlen %d\n", codelen[i]));
outbits(out, codelen[i], 3);
}
/* Code lengths for the literal/length and distance trees */
for (i = 0; i < ntreesyms; i++)
writesym(out, treesyms[i], ht);
#ifdef STATISTICS
fprintf(stderr, "total tree size %lu bits\n",
out->bitcount - bitcount_before);
#endif
}
/* Output the actual symbols from the buffer */
for (i = 0; i < blklen; i++) {
unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
writesym(out, sym, ht);
}
/* Output the end-of-data symbol */
writesym(out, SYMPFX_LITLEN | 256, ht);
/*
* Remove all the just-output symbols from the symbol buffer by
* adjusting symstart and nsyms.
*/
out->symstart = (out->symstart + blklen) % SYMLIMIT;
out->nsyms -= blklen;
}
/*
* Give the approximate log-base-2 of an input integer, measured in
* 8ths of a bit. (I.e. this computes an integer approximation to
* 8*logbase2(x).)
*/
static int approxlog2(unsigned x)
{
int ret = 31*8;
/*
* Binary-search to get the top bit of x up to bit 31.
*/
if (x < 0x00010000U) x <<= 16, ret -= 16*8;
if (x < 0x01000000U) x <<= 8, ret -= 8*8;
if (x < 0x10000000U) x <<= 4, ret -= 4*8;
if (x < 0x40000000U) x <<= 2, ret -= 2*8;
if (x < 0x80000000U) x <<= 1, ret -= 1*8;
/*
* Now we know the logarithm we want is in [ret,ret+1).
* Determine the bottom three bits by checking against
* threshold values.
*
* (Each of these threshold values is 0x80000000 times an odd
* power of 2^(1/16). Therefore, this function rounds to
* nearest.)
*/
if (x <= 0xAD583EEAU) {
if (x <= 0x91C3D373U)
ret += (x <= 0x85AAC367U ? 0 : 1);
else
ret += (x <= 0x9EF53260U ? 2 : 3);
} else {
if (x <= 0xCE248C15U)
ret += (x <= 0xBD08A39FU ? 4 : 5);
else
ret += (x <= 0xE0CCDEECU ? 6 : x <= 0xF5257D15L ? 7 : 8);
}
return ret;
}
static void chooseblock(deflate_compress_ctx *out)
{
int freqs1[286], freqs2[30];
int i, len, bestlen, longestlen = 0;
int total1, total2;
int bestvfm;
memset(freqs1, 0, sizeof(freqs1));
memset(freqs2, 0, sizeof(freqs2));
freqs1[256] = 1; /* we're bound to need one EOB */
total1 = 1;
total2 = 0;
/*
* Iterate over all possible block lengths, computing the
* entropic coding approximation to the final length at every
* stage. We divide the result by the number of symbols
* encoded, to determine the `value for money' (overall
* bits-per-symbol count) of a block of that length.
*/
bestlen = -1;
bestvfm = 0;
len = 300 * 8; /* very approximate size of the Huffman trees */
for (i = 0; i < out->nsyms; i++) {
unsigned sym = out->syms[(out->symstart + i) % SYMLIMIT];
if (i > 0 && (sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
/*
* This is a viable point at which to end the block.
* Compute the value for money.
*/
int vfm = i * 32768 / len; /* symbols encoded per bit */
if (bestlen < 0 || vfm > bestvfm) {
bestlen = i;
bestvfm = vfm;
}
longestlen = i;
}
/*
* Increment the occurrence counter for this symbol, if
* it's in one of the Huffman alphabets and isn't extra
* bits.
*/
if ((sym & SYMPFX_MASK) == SYMPFX_LITLEN) {
sym &= ~SYMPFX_MASK;
assert(sym < lenof(freqs1));
len += freqs1[sym] * approxlog2(freqs1[sym]);
len -= total1 * approxlog2(total1);
freqs1[sym]++;
total1++;
len -= freqs1[sym] * approxlog2(freqs1[sym]);
len += total1 * approxlog2(total1);
} else if ((sym & SYMPFX_MASK) == SYMPFX_DIST) {
sym &= ~SYMPFX_MASK;
assert(sym < lenof(freqs2));
len += freqs2[sym] * approxlog2(freqs2[sym]);
len -= total2 * approxlog2(total2);
freqs2[sym]++;
total2++;
len -= freqs2[sym] * approxlog2(freqs2[sym]);
len += total2 * approxlog2(total2);
} else if ((sym & SYMPFX_MASK) == SYMPFX_EXTRABITS) {
len += 8 * ((sym &~ SYMPFX_MASK) >> SYM_EXTRABITS_SHIFT);
}
}
assert(bestlen > 0);
outblock(out, bestlen, longestlen);
}
/*
* Force the current symbol buffer to be flushed out as a single
* block.
*/
static void flushblock(deflate_compress_ctx *out)
{
/*
* No need to check that out->nsyms is a valid block length: we
* know it has to be, because flushblock() is called in between
* two matches/literals.
*/
outblock(out, out->nsyms, out->nsyms);
assert(out->nsyms == 0);
}
/*
* Place a symbol into the symbols buffer.
*/
static void outsym(deflate_compress_ctx *out, unsigned long sym)
{
assert(out->nsyms < SYMLIMIT);
out->syms[(out->symstart + out->nsyms++) % SYMLIMIT] = sym;
if (out->nsyms == SYMLIMIT)
chooseblock(out);
}
static void literal(struct LZ77Context *ectx, unsigned char c)
{
deflate_compress_ctx *out = (deflate_compress_ctx *) ectx->userdata;
outsym(out, SYMPFX_LITLEN | c);
}
static void match(struct LZ77Context *ectx, int distance, int len)
{
const coderecord *d, *l;
int i, j, k;
deflate_compress_ctx *out = (deflate_compress_ctx *) ectx->userdata;
while (len > 0) {
int thislen;
/*
* We can transmit matches of lengths 3 through 258
* inclusive. So if len exceeds 258, we must transmit in
* several steps, with 258 or less in each step.
*
* Specifically: if len >= 261, we can transmit 258 and be
* sure of having at least 3 left for the next step. And if
* len <= 258, we can just transmit len. But if len == 259
* or 260, we must transmit len-3.
*/
thislen = (len > 260 ? 258 : len <= 258 ? len : len - 3);
len -= thislen;
/*
* Binary-search to find which length code we're
* transmitting.
*/
i = -1;
j = sizeof(lencodes) / sizeof(*lencodes);
while (1) {
assert(j - i >= 2);
k = (j + i) / 2;
if (thislen < lencodes[k].min)
j = k;
else if (thislen > lencodes[k].max)
i = k;
else {
l = &lencodes[k];
break; /* found it! */
}
}
/*
* Transmit the length code.
*/
outsym(out, SYMPFX_LITLEN | l->code);
/*
* Transmit the extra bits.
*/
if (l->extrabits) {
outsym(out, (SYMPFX_EXTRABITS | (thislen - l->min) |
(l->extrabits << SYM_EXTRABITS_SHIFT)));
}
/*
* Binary-search to find which distance code we're
* transmitting.
*/
i = -1;
j = sizeof(distcodes) / sizeof(*distcodes);
while (1) {
assert(j - i >= 2);
k = (j + i) / 2;
if (distance < distcodes[k].min)
j = k;
else if (distance > distcodes[k].max)
i = k;
else {
d = &distcodes[k];
break; /* found it! */
}
}
/*
* Write the distance code.
*/
outsym(out, SYMPFX_DIST | d->code);
/*
* Transmit the extra bits.
*/
if (d->extrabits) {
outsym(out, (SYMPFX_EXTRABITS | (distance - d->min) |
(d->extrabits << SYM_EXTRABITS_SHIFT)));
}
}
}
deflate_compress_ctx *deflate_compress_new(int type)
{
deflate_compress_ctx *out;
struct LZ77Context *ectx = snew(struct LZ77Context);
lz77_init(ectx, DWINSIZE);
ectx->literal = literal;
ectx->match = match;
out = snew(deflate_compress_ctx);
out->type = type;
out->outbits = out->noutbits = 0;
out->firstblock = true;
#ifdef STATISTICS
out->bitcount = 0;
#endif
out->syms = snewn(SYMLIMIT, unsigned long);
out->symstart = out->nsyms = 0;
out->checksum = (type == DEFLATE_TYPE_ZLIB ? 1 : 0);
out->datasize = 0;
out->lastblock = false;
out->finished = false;
/*
* Build the static Huffman tables now, so we'll have them
* available every time outblock() is called.
*/
{
int i;
for (i = 0; i < (int)lenof(out->static_len1); i++)
out->static_len1[i] = (i < 144 ? 8 :
i < 256 ? 9 :
i < 280 ? 7 : 8);
for (i = 0; i < (int)lenof(out->static_len2); i++)
out->static_len2[i] = 5;
}
deflate_hufcodes(out->static_len1, out->static_code1,
lenof(out->static_code1));
deflate_hufcodes(out->static_len2, out->static_code2,
lenof(out->static_code2));
out->sht.len_litlen = out->static_len1;
out->sht.len_dist = out->static_len2;
out->sht.len_codelen = NULL;