-/*
- * Encode a chunk of pixels.
- *
- * Uses an open addressing double hashing (no chaining) on the
- * prefix code/next character combination. We do a variant of
- * Knuth's algorithm D (vol. 3, sec. 6.4) along with G. Knott's
- * relatively-prime secondary probe. Here, the modular division
- * first probe is gives way to a faster exclusive-or manipulation.
- * Also do block compression with an adaptive reset, whereby the
- * code table is cleared when the compression ratio decreases,
- * but after the table fills. The variable-length output codes
- * are re-sized at this point, and a CODE_CLEAR is generated
- * for the decoder.
- */
-static int LINKAGEMODE
-LZWEncode(TIFF* tif, tidata_t bp, tsize_t cc, tsample_t s)
-{
- register LZWEncodeState *sp = EncoderState(tif);
- register long fcode;
- register hash_t *hp;
- register int h, c;
- hcode_t ent;
- long disp;
- long incount, outcount, checkpoint;
- long nextdata, nextbits;
- int free_ent, maxcode, nbits;
- tidata_t op, limit;
-
- (void) s;
- if (sp == NULL)
- return (0);
- /*
- * Load local state.
- */
- incount = sp->enc_incount;
- outcount = sp->enc_outcount;
- checkpoint = sp->enc_checkpoint;
- nextdata = sp->lzw_nextdata;
- nextbits = sp->lzw_nextbits;
- free_ent = sp->lzw_free_ent;
- maxcode = sp->lzw_maxcode;
- nbits = sp->lzw_nbits;
- op = tif->tif_rawcp;
- limit = sp->enc_rawlimit;
- ent = sp->enc_oldcode;
-
- if (ent == (hcode_t) -1 && cc > 0) {
- /*
- * NB: This is safe because it can only happen
- * at the start of a strip where we know there
- * is space in the data buffer.
- */
- PutNextCode(op, CODE_CLEAR);
- ent = *bp++; cc--; incount++;
- }
- while (cc > 0) {
- c = *bp++; cc--; incount++;
- fcode = ((long)c << BITS_MAX) + ent;
- h = (c << HSHIFT) ^ ent; /* xor hashing */
-#ifdef _WINDOWS
- /*
- * Check hash index for an overflow.
- */
- if (h >= HSIZE)
- h -= HSIZE;
-#endif
- hp = &sp->enc_hashtab[h];
- if (hp->hash == fcode) {
- ent = hp->code;
- continue;
- }
- if (hp->hash >= 0) {
- /*
- * Primary hash failed, check secondary hash.
- */
- disp = HSIZE - h;
- if (h == 0)
- disp = 1;
- do {
- /*
- * Avoid pointer arithmetic 'cuz of
- * wraparound problems with segments.
- */
- if ((h -= disp) < 0)
- h += HSIZE;
- hp = &sp->enc_hashtab[h];
- if (hp->hash == fcode) {
- ent = hp->code;
- goto hit;
- }
- } while (hp->hash >= 0);
- }
- /*
- * New entry, emit code and add to table.
- */
- /*
- * Verify there is space in the buffer for the code
- * and any potential Clear code that might be emitted
- * below. The value of limit is setup so that there
- * are at least 4 bytes free--room for 2 codes.
- */
- if (op > limit) {
- tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
- TIFFFlushData1(tif);
- op = tif->tif_rawdata;
- }
- PutNextCode(op, ent);
- ent = c;
- hp->code = free_ent++;
- hp->hash = fcode;
- if (free_ent == CODE_MAX-1) {
- /* table is full, emit clear code and reset */
- cl_hash(sp);
- sp->enc_ratio = 0;
- incount = 0;
- outcount = 0;
- free_ent = CODE_FIRST;
- PutNextCode(op, CODE_CLEAR);
- nbits = BITS_MIN;
- maxcode = MAXCODE(BITS_MIN);
- } else {
- /*
- * If the next entry is going to be too big for
- * the code size, then increase it, if possible.
- */
- if (free_ent > maxcode) {
- nbits++;
- assert(nbits <= BITS_MAX);
- maxcode = (int) MAXCODE(nbits);
- } else if (incount >= checkpoint) {
- long rat;
- /*
- * Check compression ratio and, if things seem
- * to be slipping, clear the hash table and
- * reset state. The compression ratio is a
- * 24+8-bit fractional number.
- */
- checkpoint = incount+CHECK_GAP;
- CALCRATIO(sp, rat);
- if (rat <= sp->enc_ratio) {
- cl_hash(sp);
- sp->enc_ratio = 0;
- incount = 0;
- outcount = 0;
- free_ent = CODE_FIRST;
- PutNextCode(op, CODE_CLEAR);
- nbits = BITS_MIN;
- maxcode = MAXCODE(BITS_MIN);
- } else
- sp->enc_ratio = rat;
- }
- }
- hit:
- ;
- }
-
- /*
- * Restore global state.
- */
- sp->enc_incount = incount;
- sp->enc_outcount = outcount;
- sp->enc_checkpoint = checkpoint;
- sp->enc_oldcode = ent;
- sp->lzw_nextdata = nextdata;
- sp->lzw_nextbits = nextbits;
- sp->lzw_free_ent = free_ent;
- sp->lzw_maxcode = maxcode;
- sp->lzw_nbits = nbits;
- tif->tif_rawcp = op;
- return (1);
-}
-
-/*
- * Finish off an encoded strip by flushing the last
- * string and tacking on an End Of Information code.
- */
-static int
-LZWPostEncode(TIFF* tif)
-{
- register LZWEncodeState *sp = EncoderState(tif);
- tidata_t op = tif->tif_rawcp;
- long nextbits = sp->lzw_nextbits;
- long nextdata = sp->lzw_nextdata;
- long outcount = sp->enc_outcount;
- int nbits = sp->lzw_nbits;
-
- if (op > sp->enc_rawlimit) {
- tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
- TIFFFlushData1(tif);
- op = tif->tif_rawdata;
- }
- if (sp->enc_oldcode != (hcode_t) -1) {
- PutNextCode(op, sp->enc_oldcode);
- sp->enc_oldcode = (hcode_t) -1;
- }
- PutNextCode(op, CODE_EOI);
- if (nextbits > 0)
- *op++ = (u_char)(nextdata << (8-nextbits));
- tif->tif_rawcc = (tsize_t)(op - tif->tif_rawdata);
- return (1);
-}
-
-/*
- * Reset encoding hash table.
- */
projects / wxWidgets.git / blobdiff