diff options
Diffstat (limited to 'source/fitz/filter-lzw.c')
| -rw-r--r-- | source/fitz/filter-lzw.c | 224 |
1 files changed, 224 insertions, 0 deletions
diff --git a/source/fitz/filter-lzw.c b/source/fitz/filter-lzw.c new file mode 100644 index 00000000..73909ca1 --- /dev/null +++ b/source/fitz/filter-lzw.c @@ -0,0 +1,224 @@ +#include "mupdf/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 (next_code >= NUM_CODES && code != LZW_CLEAR) + { + fz_warn(stm->ctx, "missing clear code in lzw decode"); + code = LZW_CLEAR; + } + + 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 if (code > next_code || next_code >= NUM_CODES) + { + fz_warn(stm->ctx, "out of range code encountered in lzw decode"); + } + 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; + } + + 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); +} |