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lzx.c
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lzx.c
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#include <assert.h>
#include <stddef.h>
#include "halibut.h"
#include "huffman.h"
#include "lz77.h"
#include "lzx.h"
#define OUR_LZX_WINSIZE 0x10000
#define LZX_MINMATCHLEN 2
#define LZX_MAXMATCHLEN 257
int lzx_compute_position_slot(int pos, int *footer_bits)
{
if (pos < 4) {
/* The bottom four position slots cover one value each. */
*footer_bits = 0;
return pos;
} else if (pos >= 0x40000) {
/* _All_ slots from 36 onwards are 2^17 values wide. */
*footer_bits = 17;
return 34 + (pos >> 17);
} else {
/* In between, there are two slots for each power-of-2 size,
* so that slots 4,5 have width 2^1, 6,7 have width 2^2, 8,9
* have width 2^3, ..., and 34,35 have width 2^16. */
int bits = 16;
int shifted = pos;
if (shifted < (1<<(18-8))) shifted <<= 8, bits -= 8;
if (shifted < (1<<(18-4))) shifted <<= 4, bits -= 4;
if (shifted < (1<<(18-2))) shifted <<= 2, bits -= 2;
if (shifted < (1<<(18-1))) shifted <<= 1, bits -= 1;
*footer_bits = bits;
return 2 + 2*bits + ((shifted >> 16) & 1);
}
}
typedef enum LZXSymType {
LST_MAINTREE, LST_LENTREE, LST_ALIGNOFFTREE,
LST_MAINTREE_PRETREE_1, LST_MAINTREE_PRETREE_2, LST_LENTREE_PRETREE,
LST_NTREES, dummy_enum_const = LST_NTREES-1,
LST_REALIGN_BITSTREAM,
LST_RAWBITS_BASE /* add the number of actual bits to this code */
} LZXSymType;
typedef struct LZXSym {
LZXSymType type;
int value;
} LZXSym;
typedef struct LZXBuffer {
LZXSym *syms;
int nsyms, symsize;
} LZXBuffer;
typedef struct LZXInfo {
LZXBuffer *buf;
int r0, r1, r2; /* saved match offsets */
} LZXInfo;
static void lzx_buffer_init(LZXBuffer *buf)
{
buf->syms = NULL;
buf->nsyms = buf->symsize = 0;
}
static void lzx_addsym(LZXBuffer *buf, LZXSymType type, int value)
{
if (buf->nsyms >= buf->symsize) {
assert(buf->nsyms == buf->symsize);
buf->symsize = buf->nsyms * 5 / 4 + 16384;
buf->syms = sresize(buf->syms, buf->symsize, LZXSym);
}
buf->syms[buf->nsyms].type = type;
buf->syms[buf->nsyms].value = value;
buf->nsyms++;
}
static void lzx_literal(struct LZ77Context *ctx, unsigned char c)
{
LZXBuffer *buf = ((LZXInfo *)ctx->userdata)->buf;
lzx_addsym(buf, LST_MAINTREE, c);
}
static void lzx_match(struct LZ77Context *ctx, int match_offset, int totallen)
{
LZXInfo *info = (LZXInfo *)ctx->userdata;
LZXBuffer *buf = info->buf;
/*
* First, this variant of LZX has a maximum match length of 257
* bytes, so if lz77.c reports a longer match than that, we must
* break it up.
*/
while (totallen > 0) {
int len, length_header, length_footer, len_pos_header;
int formatted_offset, position_slot, position_verbatim_bits;
int position_verbatim_value, position_aligned_offset;
if (totallen <= LZX_MAXMATCHLEN) {
/* We can emit all of the (remaining) match length in one go. */
len = totallen;
} else if (totallen >= LZX_MAXMATCHLEN+LZX_MINMATCHLEN) {
/* There's enough match left that we can emit a
* maximum-length chunk and still be assured of being able
* to emit what's left as a viable followup match. */
len = LZX_MAXMATCHLEN;
} else {
/* The in-between case, where we have _only just_ too long
* a match to emit in one go, so that if we emitted a
* max-size chunk then what's left would be under the min
* size and we couldn't emit it. */
len = totallen - LZX_MINMATCHLEN;
}
totallen -= len;
/*
* Now we're outputting a single LZX-level match of length
* 'len'. Break the length up into a 'header' (included in the
* starting LST_MAINTREE symbol) and a 'footer' (tacked on
* afterwards using LST_LENTREE).
*/
if (len < 9) {
length_header = len - 2; /* in the range {0,...,6} */
length_footer = -1; /* not transmitted at all */
} else {
length_header = 7; /* header indicates more to come */
length_footer = len - 9; /* in the range {0,...,248} */
}
/*
* Meanwhile, the raw backward distance is first transformed
* into the 'formatted offset', by either adding 2 or using
* one of the low-numbered special codes meaning to use one of
* the three most recent match distances.
*/
if (match_offset == info->r0) {
/* Reuse the most recent distance */
formatted_offset = 0;
} else if (match_offset == info->r1) {
/* Reuse the 2nd most recent, and swap it into first place */
int tmp = info->r1;
info->r1 = info->r0;
info->r0 = tmp;
formatted_offset = 1;
} else if (match_offset == info->r2) {
/* Reuse the 3rd most recent and swap it to first place.
* This is intentionally not quite a move-to-front
* shuffle, which would permute (r0,r1,r2)->(r2,r0,r1); MS
* decided that just swapping r0 with r2 was a better
* performance tradeoff. */
int tmp = info->r2;
info->r2 = info->r0;
info->r0 = tmp;
formatted_offset = 2;
} else {
/* This offset matches none of the three saved values.
* Put it in r0, and move up the rest of the list. */
info->r2 = info->r1;
info->r1 = info->r0;
info->r0 = match_offset;
formatted_offset = match_offset + 2;
}
/*
* The formatted offset now breaks up into a 'position slot'
* (encoded as part of the starting symbol) and an offset from
* the smallest position value covered by that slot. The
* system of slots is designed so that every slot's width is a
* power of two and its base value is a multiple of its width,
* so we can get the offset just by taking the bottom n bits
* of the full formatted offset, once the choice of position
* slot tells us what n is.
*/
position_slot = lzx_compute_position_slot(
formatted_offset, &position_verbatim_bits);
position_verbatim_value = formatted_offset &
((1 << position_verbatim_bits)-1);
/*
* If there are three or more additional bits, then the last 3
* of them are (potentially, depending on block type which we
* haven't decided about yet) transmitted using the aligned
* offset tree. The rest are sent verbatim.
*/
if (position_verbatim_bits >= 3) {
position_aligned_offset = position_verbatim_value & 7;
position_verbatim_bits -= 3;
position_verbatim_value >>= 3;
} else {
position_aligned_offset = -1; /* not transmitted */
}
/*
* Combine the length header and position slot into the full
* set of information encoded by the starting symbol.
*/
len_pos_header = position_slot * 8 + length_header;
/*
* And now we've finished figuring out _what_ to output, so
* output it.
*/
lzx_addsym(buf, LST_MAINTREE, 256 + len_pos_header);
if (length_footer >= 0)
lzx_addsym(buf, LST_LENTREE, length_footer);
if (position_verbatim_bits > 0)
lzx_addsym(buf, LST_RAWBITS_BASE + position_verbatim_bits,
position_verbatim_value);
if (position_aligned_offset >= 0)
lzx_addsym(buf, LST_ALIGNOFFTREE, position_aligned_offset);
}
}
void lzx_lz77_inner(LZXInfo *info, const unsigned char *data, int len)
{
struct LZ77Context lz77c;
lz77_init(&lz77c, OUR_LZX_WINSIZE);
lz77c.literal = lzx_literal;
lz77c.match = lzx_match;
lz77c.userdata = info;
lz77_compress(&lz77c, data, len, true);
lz77_cleanup(&lz77c);
}
void lzx_lz77(LZXBuffer *buf, const unsigned char *data,
int totallen, int realign_interval)
{
LZXInfo info;
info.r0 = info.r1 = info.r2 = 1;
info.buf = buf;
while (totallen > 0) {
int thislen =
totallen < realign_interval ? totallen : realign_interval;
lzx_lz77_inner(&info, data, thislen);
data += thislen;
totallen -= thislen;
if (totallen > 0)
lzx_addsym(info.buf, LST_REALIGN_BITSTREAM, 0);
}
}
typedef struct LZXHuf {
int nsyms;
unsigned char *lengths;
unsigned char *oldlengths; /* for pretree encoding to diff against */
int *codes;
} LZXHuf;
typedef struct LZXHufs {
LZXHuf hufs[LST_NTREES];
} LZXHufs;
void lzx_build_tree(LZXSym *syms, int nsyms, LZXSymType which, LZXHufs *hufs)
{
int i, max_code_len;
int *freqs;
LZXHuf *huf = &hufs->hufs[which];
switch (which) {
default:
assert(0 && "Bad lzx_build_tree tree type");
case LST_MAINTREE:
/*
* Trees encoded via a pretree have a max code length of 16,
* because that's the limit of what the pretree alphabet can
* represent.
*/
max_code_len = 16;
/*
* Number of symbols in the main tree is 256 literals, plus 8n
* match header symbols where n is the largest position slot
* number that might be needed to address any offset in the
* window.
*/
{
int ignored, last_slot;
last_slot = lzx_compute_position_slot(OUR_LZX_WINSIZE-1, &ignored);
huf->nsyms = 8 * (last_slot+1) + 256;
}
break;
case LST_LENTREE:
max_code_len = 16; /* pretree again */
huf->nsyms = 249; /* a fixed value in the spec */
break;
case LST_MAINTREE_PRETREE_1:
case LST_MAINTREE_PRETREE_2:
case LST_LENTREE_PRETREE:
/* Pretree code lengths are stored in 4-bit fields, so they
* can't go above 15. There are a standard 20 symbols in the
* pretree alphabet. */
max_code_len = 15;
huf->nsyms = 20;
break;
case LST_ALIGNOFFTREE:
/* The aligned-offset tree has 8 elements stored in 3-bit
* fields. */
max_code_len = 7;
huf->nsyms = 8;
break;
}
freqs = snewn(huf->nsyms, int);
/*
* Count up the symbol frequencies.
*/
for (i = 0; i < huf->nsyms; i++)
freqs[i] = 0;
for (i = 0; i < nsyms; i++)
if (syms[i].type == which)
freqs[syms[i].value]++;
/*
* Build the Huffman table.
*/
huf->lengths = snewn(huf->nsyms, unsigned char);
build_huffman_tree(freqs, huf->lengths, huf->nsyms, max_code_len);
huf->codes = snewn(huf->nsyms, int);
compute_huffman_codes(huf->lengths, huf->codes, huf->nsyms);
/*
* Cleanup.
*/
sfree(freqs);
}
void lzx_tree_with_pretree(LZXHuf *huf, int symoffset, int symlimit,
LZXBuffer *buf, LZXSymType pretree_symtype)
{
int i, r;
if (!huf->oldlengths) {
huf->oldlengths = snewn(huf->nsyms, unsigned char);
for (i = 0; i < huf->nsyms; i++)
huf->oldlengths[i] = 0;
}
for (i = symoffset; i < symlimit; i++) {
for (r = 1; i+r < symlimit; r++)
if (huf->lengths[i+r] != huf->lengths[i])
break;
if (r >= 4) {
/*
* We have at least one run of the same code length long
* enough to use one of the run-length encoding symbols.
*/
while (r >= 4) {
int thisrun;
if (huf->lengths[i] == 0) {
thisrun = r > 20+31 ? 20+31 : r;
if (thisrun >= 20) {
lzx_addsym(buf, pretree_symtype, 18);
lzx_addsym(buf, LST_RAWBITS_BASE + 5, thisrun - 20);
} else {
lzx_addsym(buf, pretree_symtype, 17);
lzx_addsym(buf, LST_RAWBITS_BASE + 4, thisrun - 4);
}
} else {
thisrun = r > 5 ? 5 : r;
lzx_addsym(buf, pretree_symtype, 19);
lzx_addsym(buf, LST_RAWBITS_BASE + 1, thisrun - 4);
lzx_addsym(buf, pretree_symtype,
(huf->oldlengths[i]-huf->lengths[i] + 17) % 17);
}
r -= thisrun;
i += thisrun;
}
if (r == 0) {
i--; /* compensate for normal loop increment */
continue;
}
}
/*
* Otherwise, emit a normal non-encoded symbol.
*/
lzx_addsym(buf, pretree_symtype,
(huf->oldlengths[i]-huf->lengths[i] + 17) % 17);
}
}
void lzx_tree_simple(LZXHuf *huf, LZXBuffer *buf, int bits)
{
int i;
for (i = 0; i < huf->nsyms; i++)
lzx_addsym(buf, LST_RAWBITS_BASE + bits, huf->lengths[i]);
}
typedef struct LZXBitstream {
struct LZXEncodedFile *ef;
size_t data_size, resets_size;
unsigned short bitbuffer;
int nbits;
bool first_block;
} LZXBitstream;
void lzx_write_bits(LZXBitstream *bs, int value, int bits)
{
while (bs->nbits + bits >= 16) {
int thisbits = 16 - bs->nbits;
bs->bitbuffer = (bs->bitbuffer << thisbits) |
(value >> (bits-thisbits));
if (bs->ef->data_len+2 > bs->data_size) {
bs->data_size = bs->ef->data_len * 5 / 4 + 65536;
bs->ef->data = sresize(bs->ef->data, bs->data_size,
unsigned char);
}
bs->ef->data[bs->ef->data_len++] = bs->bitbuffer;
bs->ef->data[bs->ef->data_len++] = bs->bitbuffer >> 8;
bs->bitbuffer = 0;
bs->nbits = 0;
bits -= thisbits;
value &= (1<<bits) - 1;
}
bs->bitbuffer = (bs->bitbuffer << bits) | value;
bs->nbits += bits;
}
void lzx_realign(LZXBitstream *bs)
{
lzx_write_bits(bs, 0, 15 & -(unsigned)bs->nbits);
}
void lzx_write_reset_table_entry(LZXBitstream *bs)
{
lzx_write_bits(bs, 0, 15 & -(unsigned)bs->nbits);
if (bs->ef->n_resets >= bs->resets_size) {
bs->resets_size = bs->ef->n_resets * 5 / 4 + 256;
bs->ef->reset_byte_offsets = sresize(bs->ef->reset_byte_offsets,
bs->resets_size, size_t);
}
bs->ef->reset_byte_offsets[bs->ef->n_resets++] = bs->ef->data_len;
}
void lzx_huf_encode(LZXSym *syms, int nsyms, LZXHufs *hufs, LZXBitstream *bs)
{
int i;
for (i = 0; i < nsyms; i++) {
LZXSymType type = syms[i].type;
int value = syms[i].value;
if (type >= LST_RAWBITS_BASE) {
lzx_write_bits(bs, value, type - LST_RAWBITS_BASE);
} else if (type == LST_REALIGN_BITSTREAM) {
/* Realign the bitstream to a 16-bit boundary, and write a
* reset table entry giving the resulting byte offset. */
lzx_realign(bs);
lzx_write_reset_table_entry(bs);
} else {
lzx_write_bits(bs, hufs->hufs[type].codes[value],
hufs->hufs[type].lengths[value]);
}
}
}
void lzx_encode_block(LZXSym *syms, int nsyms, int blocksize,
LZXHufs *hufs, LZXBitstream *bs)
{
LZXBuffer header[8];
int i, blocktype;
for (i = 0; i < (int)lenof(header); i++)
lzx_buffer_init(&header[i]);
/*
* Build the Huffman trees for the main alphabets used in the
* block.
*/
lzx_build_tree(syms, nsyms, LST_MAINTREE, hufs);
lzx_build_tree(syms, nsyms, LST_LENTREE, hufs);
lzx_build_tree(syms, nsyms, LST_ALIGNOFFTREE, hufs);
/*
* Encode each of those as a sequence of pretree symbols.
*/
lzx_tree_with_pretree(&hufs->hufs[LST_MAINTREE], 0, 256,
&header[3], LST_MAINTREE_PRETREE_1);
lzx_tree_with_pretree(&hufs->hufs[LST_MAINTREE], 256,
hufs->hufs[LST_MAINTREE].nsyms,
&header[5], LST_MAINTREE_PRETREE_2);
lzx_tree_with_pretree(&hufs->hufs[LST_LENTREE], 0,
hufs->hufs[LST_LENTREE].nsyms,
&header[7], LST_LENTREE_PRETREE);
/*
* Build the pretree for each of those encodings.
*/
lzx_build_tree(header[3].syms, header[3].nsyms,
LST_MAINTREE_PRETREE_1, hufs);
lzx_build_tree(header[5].syms, header[5].nsyms,
LST_MAINTREE_PRETREE_2, hufs);
lzx_build_tree(header[7].syms, header[7].nsyms,
LST_LENTREE_PRETREE, hufs);
/*
* Decide whether we're keeping the aligned offset tree or not.
*/
{
int with, without;
with = 3*8; /* cost of transmitting tree */
without = 0; /* or not */
for (i = 0; i < nsyms; i++)
if (syms[i].type == LST_ALIGNOFFTREE) {
with += hufs->hufs[LST_ALIGNOFFTREE].lengths[syms[i].value];
without += 3;
}
if (with < without) {
/* Yes, it's a win to use the aligned offset tree. */
blocktype = 2;
} else {
/* No, we do better by throwing it away. */
blocktype = 1;
/* Easiest way to simulate that is to pretend we're still
* using an aligned offset tree in the encoding, but to
* chuck away our code lengths and replace them with the
* fixed-length trivial tree. */
for (i = 0; i < 8; i++) {
hufs->hufs[LST_ALIGNOFFTREE].lengths[i] = 3;
hufs->hufs[LST_ALIGNOFFTREE].codes[i] = i;
}
}
}
/*
* Encode all the simply encoded trees (the three pretrees and the
* aligned offset tree).
*/
lzx_tree_simple(&hufs->hufs[LST_MAINTREE_PRETREE_1], &header[2], 4);
lzx_tree_simple(&hufs->hufs[LST_MAINTREE_PRETREE_2], &header[4], 4);
lzx_tree_simple(&hufs->hufs[LST_LENTREE_PRETREE], &header[6], 4);
if (blocktype == 2)
lzx_tree_simple(&hufs->hufs[LST_ALIGNOFFTREE], &header[1], 3);
/*
* Top-level block header.
*/
if (bs->first_block) {
/*
* Also include the whole-file header which says whether E8
* call translation is on. We never turn it on, because we
* don't support it (since in this use case it doesn't seem
* likely to be particularly useful anyway).
*
* It looks like a layer violation to put the output of this
* whole-file header inside the per-block function like this,
* but in fact it has to be done here because the first reset
* table entry really is supposed to point to the _start_ of
* the whole-file header.
*/
lzx_addsym(&header[0], LST_RAWBITS_BASE + 1, 0);
bs->first_block = false;
}
lzx_addsym(&header[0], LST_RAWBITS_BASE + 3, blocktype);
lzx_addsym(&header[0], LST_RAWBITS_BASE + 24, blocksize);
/*
* Ensure the bit stream starts off aligned, and output an initial
* reset-table entry.
*/
lzx_realign(bs);
lzx_write_reset_table_entry(bs);
/*
* Write out all of our symbol sequences in order: all of those
* assorted header fragments, then the main LZ77 token sequence.
*/
for (i = 0; i < (int)lenof(header); i++)
lzx_huf_encode(header[i].syms, header[i].nsyms, hufs, bs);
lzx_huf_encode(syms, nsyms, hufs, bs);
/*
* Clean up.
*/
for (i = 0; i < (int)lenof(header); i++)
sfree(header[i].syms);
for (i = 0; i < (int)lenof(hufs->hufs); i++) {
sfree(hufs->hufs[i].codes);
sfree(hufs->hufs[i].lengths);
}
}
struct LZXEncodedFile *lzx(const void *vdata, int totallen,
int realign_interval, int reset_interval)
{
const unsigned char *data = (const unsigned char *)vdata;
LZXBitstream bs;
LZXHufs hufs;
int i;
bs.ef = snew(struct LZXEncodedFile);
bs.ef->data = NULL;
bs.ef->reset_byte_offsets = NULL;
bs.ef->data_len = bs.data_size = 0;
bs.ef->n_resets = bs.resets_size = 0;
bs.bitbuffer = 0;
bs.nbits = 0;
for (i = 0; i < (int)lenof(hufs.hufs); i++)
hufs.hufs[i].oldlengths = NULL;
while (totallen > 0) {
int thislen =
totallen < reset_interval ? totallen : reset_interval;
LZXBuffer buf;
lzx_buffer_init(&buf);
lzx_lz77(&buf, data, thislen, realign_interval);
data += thislen;
totallen -= thislen;
/*
* Block boundaries are chosen completely trivially: since we
* have to terminate a block every time we reach the (fairly
* short) reset interval in any case, it doesn't hurt us much
* to just fix the assumption that every (reset_interval)
* bytes of the input turn into exactly one block, i.e. the
* whole of buf.syms that we just constructed is output in one
* go. We _could_ try improving on this by clever
* block-boundary heuristics, but I don't really think it's
* worth it.
*/
bs.first_block = true; /* reset every time we reset the LZ state */
lzx_encode_block(buf.syms, buf.nsyms, thislen, &hufs, &bs);
sfree(buf.syms);
}
for (i = 0; i < (int)lenof(hufs.hufs); i++)
sfree(hufs.hufs[i].oldlengths);
/* Realign to a 16-bit boundary, i.e. flush out any last few
* unwritten bits. */
lzx_realign(&bs);
return bs.ef;
}
#ifdef LZX_TEST
/*
gcc -g -O0 -DLZX_TEST -o lzxtest -Icharset lzx.c lz77.c huffman.c malloc.c
*/
#include <err.h>
int main(int argc, char **argv)
{
FILE *fp;
long insize;
unsigned char *inbuf;
struct LZXEncodedFile *ef;
if (argc != 3)
errx(1, "expected infile and outfile arguments");
fp = fopen(argv[1], "rb");
if (!fp)
err(1, "%s: open", argv[1]);
fseek(fp, 0, SEEK_END);
insize = ftell(fp);
rewind(fp);
inbuf = snewn(insize, unsigned char);
fread(inbuf, 1, insize, fp);
fclose(fp);
ef = lzx(inbuf, insize, 0x8000, 0x10000);
fp = fopen(argv[2], "wb");
if (!fp)
err(1, "%s: open", argv[2]);
fwrite(ef->data, 1, ef->data_len, fp);
fclose(fp);
sfree(ef->data);
sfree(ef->reset_byte_offsets);
sfree(ef);
sfree(inbuf);
return 0;
}
wchar_t *ustrdup(wchar_t const *s) { assert(0 && "should be unused"); }
void fatalerr_nomemory(void) { errx(1, "out of memory"); }
#endif