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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
};
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_filter super;
int earlychange;
unsigned int word; /* bits loaded from data */
int bidx;
int resume; /* resume output of code from needout */
int codebits; /* num bits/code */
int code; /* current code */
int oldcode; /* previously recognized code */
int nextcode; /* next free entry */
lzw_code table[NUMCODES];
};
fz_filter *
fz_newlzwd(fz_obj *params)
{
int i;
FZ_NEWFILTER(fz_lzwd, lzw, lzwd);
lzw->earlychange = 1;
if (params)
{
fz_obj *obj;
obj = fz_dictgets(params, "EarlyChange");
if (obj) lzw->earlychange = fz_toint(obj) != 0;
}
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->resume = 0;
return (fz_filter *)lzw;
}
void
fz_droplzwd(fz_filter *filter)
{
}
static inline void eatbits(fz_lzwd *lzw, int nbits)
{
lzw->word <<= nbits;
lzw->bidx += nbits;
}
static inline fz_error fillbits(fz_lzwd *lzw, fz_buffer *in)
{
while (lzw->bidx >= 8)
{
if (in->rp + 1 > in->wp)
return fz_ioneedin;
lzw->bidx -= 8;
lzw->word |= *in->rp << lzw->bidx;
in->rp ++;
}
return fz_okay;
}
static inline void unstuff(fz_lzwd *lzw, fz_buffer *in)
{
int i = (32 - lzw->bidx) / 8;
while (i-- && in->rp > in->bp)
in->rp --;
}
fz_error
fz_processlzwd(fz_filter *filter, fz_buffer *in, fz_buffer *out)
{
fz_lzwd *lzw = (fz_lzwd*)filter;
unsigned char *s;
int len;
if (lzw->resume)
{
lzw->resume = 0;
goto output;
}
while (1)
{
if (fillbits(lzw, in))
{
if (in->eof)
{
if (lzw->bidx > 32 - lzw->codebits)
{
unstuff(lzw, in);
return fz_iodone;
}
}
else
{
return fz_ioneedin;
}
}
lzw->code = lzw->word >> (32 - lzw->codebits);
lzw->code &= (1 << lzw->codebits) - 1;
eatbits(lzw, lzw->codebits);
if (lzw->code == LZW_EOD)
{
unstuff(lzw, in);
return fz_iodone;
}
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)
{
if (out->wp + lzw->table[lzw->code].length > out->ep)
{
lzw->resume = 1;
return fz_ioneedout;
}
len = lzw->table[lzw->code].length;
s = out->wp + len;
do
{
*(--s) = lzw->table[lzw->code].value;
lzw->code = lzw->table[lzw->code].prev;
} while (lzw->code >= 0 && s > out->wp);
out->wp += len;
}
/* ... or just a single character */
else
{
if (out->wp + 1 > out->ep)
{
lzw->resume = 1;
return fz_ioneedout;
}
*out->wp++ = lzw->code;
}
}
}
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