tif_lzw.c

这是VCF框架的代码

		op += residue, occ -= residue;
		tp = op;
		do {
			int t;
			--tp;
			t = codep->value;
			codep = codep->next;
			*tp = t;
		} while (--residue && codep);
		sp->dec_restart = 0;
	}

	bp = (u_char *)tif->tif_rawcp;
	nbits = sp->lzw_nbits;
	nextdata = sp->lzw_nextdata;
	nextbits = sp->lzw_nextbits;
	nbitsmask = sp->dec_nbitsmask;
	oldcodep = sp->dec_oldcodep;
	free_entp = sp->dec_free_entp;
	maxcodep = sp->dec_maxcodep;

	while (occ > 0) {
		NextCode(tif, sp, bp, code, GetNextCode);
		if (code == CODE_EOI)
			break;
		if (code == CODE_CLEAR) {
			free_entp = sp->dec_codetab + CODE_FIRST;
			nbits = BITS_MIN;
			nbitsmask = MAXCODE(BITS_MIN);
			maxcodep = sp->dec_codetab + nbitsmask-1;
			NextCode(tif, sp, bp, code, GetNextCode);
			if (code == CODE_EOI)
				break;
			*op++ = (char)code, occ--;
			oldcodep = sp->dec_codetab + code;
			continue;
		}
		codep = sp->dec_codetab + code;

		/*
	 	 * Add the new entry to the code table.
	 	 */
		assert(&sp->dec_codetab[0] <= free_entp && free_entp < &sp->dec_codetab[CSIZE]);
		free_entp->next = oldcodep;
		free_entp->firstchar = free_entp->next->firstchar;
		free_entp->length = free_entp->next->length+1;
		free_entp->value = (codep < free_entp) ?
		    codep->firstchar : free_entp->firstchar;
		if (++free_entp > maxcodep) {
			if (++nbits > BITS_MAX)		/* should not happen */
				nbits = BITS_MAX;
			nbitsmask = MAXCODE(nbits);
			maxcodep = sp->dec_codetab + nbitsmask-1;
		}
		oldcodep = codep;
		if (code >= 256) {
			/*
		 	 * Code maps to a string, copy string
			 * value to output (written in reverse).
		 	 */
			if (codep->length > occ) {
				/*
				 * String is too long for decode buffer,
				 * locate portion that will fit, copy to
				 * the decode buffer, and setup restart
				 * logic for the next decoding call.
				 */
				sp->dec_codep = codep;
				do {
					codep = codep->next;
				} while (codep && codep->length > occ);
				if (codep) {
					sp->dec_restart = occ;
					tp = op + occ;
					do  {
						*--tp = codep->value;
						codep = codep->next;
					}  while (--occ && codep);
					if (codep)
						codeLoop(tif);
				}
				break;
			}
			len = codep->length;
			tp = op + len;
			do {
				int t;
				--tp;
				t = codep->value;
				codep = codep->next;
				*tp = t;
			} while (codep && tp > op);
			if (codep) {
			    codeLoop(tif);
			    break;
			}
			op += len, occ -= len;
		} else
			*op++ = (char)code, occ--;
	}

	tif->tif_rawcp = (tidata_t) bp;
	sp->lzw_nbits = (u_short) nbits;
	sp->lzw_nextdata = nextdata;
	sp->lzw_nextbits = nextbits;
	sp->dec_nbitsmask = nbitsmask;
	sp->dec_oldcodep = oldcodep;
	sp->dec_free_entp = free_entp;
	sp->dec_maxcodep = maxcodep;

	if (occ > 0) {
		TIFFError(tif->tif_name,
		"LZWDecode: Not enough data at scanline %d (short %d bytes)",
		    tif->tif_row, occ);
		return (0);
	}
	return (1);
}

#ifdef LZW_COMPAT
/*
 * Decode a "hunk of data" for old images.
 */
#define	GetNextCodeCompat(sp, bp, code) {			\
	nextdata |= (u_long) *(bp)++ << nextbits;		\
	nextbits += 8;						\
	if (nextbits < nbits) {					\
		nextdata |= (u_long) *(bp)++ << nextbits;	\
		nextbits += 8;					\
	}							\
	code = (hcode_t)(nextdata & nbitsmask);			\
	nextdata >>= nbits;					\
	nextbits -= nbits;					\
}

static int
LZWDecodeCompat(TIFF* tif, tidata_t op0, tsize_t occ0, tsample_t s)
{
	LZWDecodeState *sp = DecoderState(tif);
	char *op = (char*) op0;
	long occ = (long) occ0;
	char *tp;
	u_char *bp;
	int code, nbits;
	long nextbits, nextdata, nbitsmask;
	code_t *codep, *free_entp, *maxcodep, *oldcodep;

	(void) s;
	assert(sp != NULL);
	/*
	 * Restart interrupted output operation.
	 */
	if (sp->dec_restart) {
		long residue;

		codep = sp->dec_codep;
		residue = codep->length - sp->dec_restart;
		if (residue > occ) {
			/*
			 * Residue from previous decode is sufficient
			 * to satisfy decode request.  Skip to the
			 * start of the decoded string, place decoded
			 * values in the output buffer, and return.
			 */
			sp->dec_restart += occ;
			do {
				codep = codep->next;
			} while (--residue > occ);
			tp = op + occ;
			do {
				*--tp = codep->value;
				codep = codep->next;
			} while (--occ);
			return (1);
		}
		/*
		 * Residue satisfies only part of the decode request.
		 */
		op += residue, occ -= residue;
		tp = op;
		do {
			*--tp = codep->value;
			codep = codep->next;
		} while (--residue);
		sp->dec_restart = 0;
	}

	bp = (u_char *)tif->tif_rawcp;
	nbits = sp->lzw_nbits;
	nextdata = sp->lzw_nextdata;
	nextbits = sp->lzw_nextbits;
	nbitsmask = sp->dec_nbitsmask;
	oldcodep = sp->dec_oldcodep;
	free_entp = sp->dec_free_entp;
	maxcodep = sp->dec_maxcodep;

	while (occ > 0) {
		NextCode(tif, sp, bp, code, GetNextCodeCompat);
		if (code == CODE_EOI)
			break;
		if (code == CODE_CLEAR) {
			free_entp = sp->dec_codetab + CODE_FIRST;
			nbits = BITS_MIN;
			nbitsmask = MAXCODE(BITS_MIN);
			maxcodep = sp->dec_codetab + nbitsmask;
			NextCode(tif, sp, bp, code, GetNextCodeCompat);
			if (code == CODE_EOI)
				break;
			*op++ = code, occ--;
			oldcodep = sp->dec_codetab + code;
			continue;
		}
		codep = sp->dec_codetab + code;

		/*
	 	 * Add the new entry to the code table.
	 	 */
		assert(&sp->dec_codetab[0] <= free_entp && free_entp < &sp->dec_codetab[CSIZE]);
		free_entp->next = oldcodep;
		free_entp->firstchar = free_entp->next->firstchar;
		free_entp->length = free_entp->next->length+1;
		free_entp->value = (codep < free_entp) ?
		    codep->firstchar : free_entp->firstchar;
		if (++free_entp > maxcodep) {
			if (++nbits > BITS_MAX)		/* should not happen */
				nbits = BITS_MAX;
			nbitsmask = MAXCODE(nbits);
			maxcodep = sp->dec_codetab + nbitsmask;
		}
		oldcodep = codep;
		if (code >= 256) {
			/*
		 	 * Code maps to a string, copy string
			 * value to output (written in reverse).
		 	 */
			if (codep->length > occ) {
				/*
				 * String is too long for decode buffer,
				 * locate portion that will fit, copy to
				 * the decode buffer, and setup restart
				 * logic for the next decoding call.
				 */
				sp->dec_codep = codep;
				do {
					codep = codep->next;
				} while (codep->length > occ);
				sp->dec_restart = occ;
				tp = op + occ;
				do  {
					*--tp = codep->value;
					codep = codep->next;
				}  while (--occ);
				break;
			}
			op += codep->length, occ -= codep->length;
			tp = op;
			do {
				*--tp = codep->value;
			} while( (codep = codep->next) != NULL);
		} else
			*op++ = code, occ--;
	}

	tif->tif_rawcp = (tidata_t) bp;
	sp->lzw_nbits = nbits;
	sp->lzw_nextdata = nextdata;
	sp->lzw_nextbits = nextbits;
	sp->dec_nbitsmask = nbitsmask;
	sp->dec_oldcodep = oldcodep;
	sp->dec_free_entp = free_entp;
	sp->dec_maxcodep = maxcodep;

	if (occ > 0) {
		TIFFError(tif->tif_name,
	    "LZWDecodeCompat: Not enough data at scanline %d (short %d bytes)",
		    tif->tif_row, occ);
		return (0);
	}
	return (1);
}
#endif /* LZW_COMPAT */



static void
LZWCleanup(TIFF* tif)
{
	if (tif->tif_data) {
		if (tif->tif_mode == O_RDONLY) {
			if (DecoderState(tif)->dec_codetab)
				_TIFFfree(DecoderState(tif)->dec_codetab);
		}
		_TIFFfree(tif->tif_data);
		tif->tif_data = NULL;
	}
}

int
TIFFInitLZW(TIFF* tif, int scheme)
{
	assert(scheme == COMPRESSION_LZW);
	/*
	 * Allocate state block so tag methods have storage to record values.
	 */
	if (tif->tif_mode == O_RDONLY) {
		tif->tif_data = (tidata_t) _TIFFmalloc(sizeof (LZWDecodeState));
		if (tif->tif_data == NULL)
			goto bad;
		DecoderState(tif)->dec_codetab = NULL;
		DecoderState(tif)->dec_decode = NULL;
	} 

	/*
	 * Install codec methods.
	 */
	tif->tif_setupdecode = LZWSetupDecode;
	tif->tif_predecode = LZWPreDecode;
	tif->tif_decoderow = LZWDecode;
	tif->tif_decodestrip = LZWDecode;
	tif->tif_decodetile = LZWDecode;
	tif->tif_cleanup = LZWCleanup;
	/*
	 * Setup predictor setup.
	 */
	(void) TIFFPredictorInit(tif);
	return (1);
bad:
	TIFFError("TIFFInitLZW", "No space for LZW state block");
	return (0);
}

/*
 * Copyright (c) 1985, 1986 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * James A. Woods, derived from original work by Spencer Thomas
 * and Joseph Orost.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that the above copyright notice and this paragraph are
 * duplicated in all such forms and that any documentation,
 * advertising materials, and other materials related to such
 * distribution and use acknowledge that the software was developed
 * by the University of California, Berkeley.  The name of the
 * University may not be used to endorse or promote products derived
 * from this software without specific prior written permission.
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 */
#endif /* LZW_SUPPORT */