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#include "fitz.h"
/* TODO: error checking */
enum
{
MINBITS = 9,
MAXBITS = 12,
NUMCODES = (1 << MAXBITS),
LZW_CLEAR = 256,
LZW_EOD = 257,
LZW_FIRST = 258,
MAXLENGTH = 4097
};
typedef struct lzw_code_s lzw_code;
struct lzw_code_s
{
int prev; /* prev code (in string) */
unsigned short length; /* string len, including this token */
unsigned char value; /* data value */
unsigned char firstchar; /* first token of string */
};
typedef struct fz_lzwd_s fz_lzwd;
struct fz_lzwd_s
{
fz_stream *chain;
int eod;
int earlychange;
unsigned int word; /* bits loaded from data */
int bidx;
int codebits; /* num bits/code */
int code; /* current code */
int oldcode; /* previously recognized code */
int nextcode; /* next free entry */
lzw_code table[NUMCODES];
unsigned char bp[MAXLENGTH];
unsigned char *rp, *wp;
};
static inline void eatbits(fz_lzwd *lzw, int nbits)
{
lzw->word <<= nbits;
lzw->bidx += nbits;
}
static inline int fillbits(fz_lzwd *lzw)
{
while (lzw->bidx >= 8)
{
int c = fz_readbyte(lzw->chain);
if (c == EOF)
return EOF;
lzw->bidx -= 8;
lzw->word |= c << lzw->bidx;
}
return 0;
}
static int
readlzwd(fz_stream *stm, unsigned char *buf, int len)
{
fz_lzwd *lzw = stm->state;
unsigned char *p = buf;
unsigned char *ep = buf + len;
unsigned char *s;
int codelen;
while (lzw->rp < lzw->wp && p < ep)
*p++ = *lzw->rp++;
while (p < ep)
{
if (lzw->eod)
return 0;
if (fillbits(lzw))
{
if (lzw->bidx > 32 - lzw->codebits)
{
lzw->eod = 1;
return p - buf;
}
}
lzw->code = lzw->word >> (32 - lzw->codebits);
lzw->code &= (1 << lzw->codebits) - 1;
eatbits(lzw, lzw->codebits);
if (lzw->code == LZW_EOD)
{
lzw->eod = 1;
return p - buf;
}
if (lzw->code == LZW_CLEAR)
{
lzw->codebits = MINBITS;
lzw->nextcode = LZW_FIRST;
lzw->oldcode = -1;
continue;
}
/* if stream starts without a clear code, oldcode is undefined... */
if (lzw->oldcode == -1)
{
lzw->oldcode = lzw->code;
goto output;
}
/* add new entry to the code table */
lzw->table[lzw->nextcode].prev = lzw->oldcode;
lzw->table[lzw->nextcode].firstchar = lzw->table[lzw->oldcode].firstchar;
lzw->table[lzw->nextcode].length = lzw->table[lzw->oldcode].length + 1;
if (lzw->code < lzw->nextcode)
lzw->table[lzw->nextcode].value = lzw->table[lzw->code].firstchar;
else if (lzw->code == lzw->nextcode)
lzw->table[lzw->nextcode].value = lzw->table[lzw->nextcode].firstchar;
else
fz_warn("out of range code encountered in lzw decode");
lzw->nextcode ++;
if (lzw->nextcode > (1 << lzw->codebits) - lzw->earlychange - 1)
{
lzw->codebits ++;
if (lzw->codebits > MAXBITS)
lzw->codebits = MAXBITS; /* FIXME */
}
lzw->oldcode = lzw->code;
output:
/* code maps to a string, copy to output (in reverse...) */
if (lzw->code > 255)
{
codelen = lzw->table[lzw->code].length;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp + codelen;
assert(codelen < MAXLENGTH);
s = lzw->wp;
do {
*(--s) = lzw->table[lzw->code].value;
lzw->code = lzw->table[lzw->code].prev;
} while (lzw->code >= 0 && s > lzw->bp);
}
/* ... or just a single character */
else
{
lzw->bp[0] = lzw->code;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp + 1;
}
/* copy to output */
while (lzw->rp < lzw->wp && p < ep)
*p++ = *lzw->rp++;
}
return p - buf;
}
static void
closelzwd(fz_stream *stm)
{
fz_lzwd *lzw = stm->state;
int i;
/* if we read any extra bytes, try to put them back */
i = (32 - lzw->bidx) / 8;
while (i--)
fz_unreadbyte(lzw->chain);
fz_close(lzw->chain);
fz_free(lzw);
}
fz_stream *
fz_openlzwd(fz_stream *chain, fz_obj *params)
{
fz_lzwd *lzw;
fz_obj *obj;
int i;
lzw = fz_malloc(sizeof(fz_lzwd));
lzw->chain = chain;
lzw->eod = 0;
lzw->earlychange = 1;
obj = fz_dictgets(params, "EarlyChange");
if (obj)
lzw->earlychange = !!fz_toint(obj);
lzw->bidx = 32;
lzw->word = 0;
for (i = 0; i < 256; i++)
{
lzw->table[i].value = i;
lzw->table[i].firstchar = i;
lzw->table[i].length = 1;
lzw->table[i].prev = -1;
}
for (i = 256; i < NUMCODES; i++)
{
lzw->table[i].value = 0;
lzw->table[i].firstchar = 0;
lzw->table[i].length = 0;
lzw->table[i].prev = -1;
}
lzw->codebits = MINBITS;
lzw->code = -1;
lzw->nextcode = LZW_FIRST;
lzw->oldcode = -1;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp;
return fz_newstream(lzw, readlzwd, closelzwd);
}
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