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#include "fitz.h"
/* TODO: error checking */
enum
{
MIN_BITS = 9,
MAX_BITS = 12,
NUM_CODES = (1 << MAX_BITS),
LZW_CLEAR = 256,
LZW_EOD = 257,
LZW_FIRST = 258,
MAX_LENGTH = 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 first_char; /* first token of string */
};
typedef struct fz_lzwd_s fz_lzwd;
struct fz_lzwd_s
{
fz_stream *chain;
int eod;
int early_change;
int code_bits; /* num bits/code */
int code; /* current code */
int old_code; /* previously recognized code */
int next_code; /* next free entry */
lzw_code table[NUM_CODES];
unsigned char bp[MAX_LENGTH];
unsigned char *rp, *wp;
};
static int
read_lzwd(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 code_bits = lzw->code_bits;
int code = lzw->code;
int old_code = lzw->old_code;
int next_code = lzw->next_code;
while (lzw->rp < lzw->wp && p < ep)
*p++ = *lzw->rp++;
while (p < ep)
{
if (lzw->eod)
return 0;
code = fz_read_bits(lzw->chain, code_bits);
if (fz_is_eof_bits(lzw->chain))
{
lzw->eod = 1;
break;
}
if (code == LZW_EOD)
{
lzw->eod = 1;
break;
}
if (code == LZW_CLEAR)
{
code_bits = MIN_BITS;
next_code = LZW_FIRST;
old_code = -1;
continue;
}
/* if stream starts without a clear code, old_code is undefined... */
if (old_code == -1)
{
old_code = code;
}
else
{
/* add new entry to the code table */
table[next_code].prev = old_code;
table[next_code].first_char = table[old_code].first_char;
table[next_code].length = table[old_code].length + 1;
if (code < next_code)
table[next_code].value = table[code].first_char;
else if (code == next_code)
table[next_code].value = table[next_code].first_char;
else
fz_warn(stm->ctx, "out of range code encountered in lzw decode");
next_code ++;
if (next_code > (1 << code_bits) - lzw->early_change - 1)
{
code_bits ++;
if (code_bits > MAX_BITS)
code_bits = MAX_BITS; /* FIXME */
}
old_code = 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 < MAX_LENGTH);
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->code_bits = code_bits;
lzw->code = code;
lzw->old_code = old_code;
lzw->next_code = next_code;
return p - buf;
}
static void
close_lzwd(fz_context *ctx, void *state_)
{
fz_lzwd *lzw = (fz_lzwd *)state_;
fz_close(lzw->chain);
fz_free(ctx, lzw);
}
/* Default: early_change = 1 */
fz_stream *
fz_open_lzwd(fz_stream *chain, int early_change)
{
fz_context *ctx = chain->ctx;
fz_lzwd *lzw = NULL;
int i;
fz_var(lzw);
fz_try(ctx)
{
lzw = fz_malloc_struct(ctx, fz_lzwd);
lzw->chain = chain;
lzw->eod = 0;
lzw->early_change = early_change;
for (i = 0; i < 256; i++)
{
lzw->table[i].value = i;
lzw->table[i].first_char = i;
lzw->table[i].length = 1;
lzw->table[i].prev = -1;
}
for (i = 256; i < NUM_CODES; i++)
{
lzw->table[i].value = 0;
lzw->table[i].first_char = 0;
lzw->table[i].length = 0;
lzw->table[i].prev = -1;
}
lzw->code_bits = MIN_BITS;
lzw->code = -1;
lzw->next_code = LZW_FIRST;
lzw->old_code = -1;
lzw->rp = lzw->bp;
lzw->wp = lzw->bp;
}
fz_catch(ctx)
{
fz_free(ctx, lzw);
fz_close(chain);
fz_rethrow(ctx);
}
return fz_new_stream(ctx, lzw, read_lzwd, close_lzwd);
}
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