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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;
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 int
readlzwd(fz_stream *stm, unsigned char *buf, int len)
{
fz_lzwd *lzw = stm->state;
lzw_code *table = lzw->table;
unsigned char *p = buf;
unsigned char *ep = buf + len;
unsigned char *s;
int codelen;
int codebits = lzw->codebits;
int code = lzw->code;
int oldcode = lzw->oldcode;
int nextcode = lzw->nextcode;
while (lzw->rp < lzw->wp && p < ep)
*p++ = *lzw->rp++;
while (p < ep)
{
if (lzw->eod)
return 0;
code = fz_readbits(lzw->chain, codebits);
if (fz_iseofbits(lzw->chain))
{
lzw->eod = 1;
break;
}
if (code == LZW_EOD)
{
lzw->eod = 1;
break;
}
if (code == LZW_CLEAR)
{
codebits = MINBITS;
nextcode = LZW_FIRST;
oldcode = -1;
continue;
}
/* if stream starts without a clear code, oldcode is undefined... */
if (oldcode == -1)
{
oldcode = code;
}
else
{
/* add new entry to the code table */
table[nextcode].prev = oldcode;
table[nextcode].firstchar = table[oldcode].firstchar;
table[nextcode].length = table[oldcode].length + 1;
if (code < nextcode)
table[nextcode].value = table[code].firstchar;
else if (code == nextcode)
table[nextcode].value = table[nextcode].firstchar;
else
fz_warn("out of range code encountered in lzw decode");
nextcode ++;
if (nextcode > (1 << codebits) - lzw->earlychange - 1)
{
codebits ++;
if (codebits > MAXBITS)
codebits = MAXBITS; /* FIXME */
}
oldcode = code;
}
/* code maps to a string, copy to output (in reverse...) */
if (code > 255)
{
codelen = table[code].length;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp + codelen;
assert(codelen < MAXLENGTH);
s = lzw->wp;
do {
*(--s) = table[code].value;
code = table[code].prev;
} while (code >= 0 && s > lzw->bp);
}
/* ... or just a single character */
else
{
lzw->bp[0] = code;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp + 1;
}
/* copy to output */
while (lzw->rp < lzw->wp && p < ep)
*p++ = *lzw->rp++;
}
lzw->codebits = codebits;
lzw->code = code;
lzw->oldcode = oldcode;
lzw->nextcode = nextcode;
return p - buf;
}
static void
closelzwd(fz_stream *stm)
{
fz_lzwd *lzw = stm->state;
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);
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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