fs/jffs2/mini_inflate.c - filogic/uboot - Gitiles

 // SPDX-License-Identifier: GPL-2.0+
 /*-------------------------------------------------------------------------
  * Filename:      mini_inflate.c
  * Version:       $Id: mini_inflate.c,v 1.3 2002/01/24 22:58:42 rfeany Exp $
  * Copyright:     Copyright (C) 2001, Russ Dill
  * Author:        Russ Dill <Russ.Dill@asu.edu>
  * Description:   Mini inflate implementation (RFC 1951)
  *-----------------------------------------------------------------------*/

 #include <config.h>
 #include <jffs2/mini_inflate.h>

 /* The order that the code lengths in section 3.2.7 are in */
 static unsigned char huffman_order[] = {16, 17, 18,  0,  8,  7,  9,  6, 10,  5,
 					11,  4, 12,  3, 13,  2, 14,  1, 15};

 static inline void cramfs_memset(int *s, const int c, size n)
 {
 	n--;
 	for (;n > 0; n--) s[n] = c;
 	s[0] = c;
 }

 /* associate a stream with a block of data and reset the stream */
 static void init_stream(struct bitstream *stream, unsigned char *data,
 			void *(*inflate_memcpy)(void *, const void *, size))
 {
 	stream->error = NO_ERROR;
 	stream->memcpy = inflate_memcpy;
 	stream->decoded = 0;
 	stream->data = data;
 	stream->bit = 0;	/* The first bit of the stream is the lsb of the
 				 * first byte */

 	/* really sorry about all this initialization, think of a better way,
 	 * let me know and it will get cleaned up */
 	stream->codes.bits = 8;
 	stream->codes.num_symbols = 19;
 	stream->codes.lengths = stream->code_lengths;
 	stream->codes.symbols = stream->code_symbols;
 	stream->codes.count = stream->code_count;
 	stream->codes.first = stream->code_first;
 	stream->codes.pos = stream->code_pos;

 	stream->lengths.bits = 16;
 	stream->lengths.num_symbols = 288;
 	stream->lengths.lengths = stream->length_lengths;
 	stream->lengths.symbols = stream->length_symbols;
 	stream->lengths.count = stream->length_count;
 	stream->lengths.first = stream->length_first;
 	stream->lengths.pos = stream->length_pos;

 	stream->distance.bits = 16;
 	stream->distance.num_symbols = 32;
 	stream->distance.lengths = stream->distance_lengths;
 	stream->distance.symbols = stream->distance_symbols;
 	stream->distance.count = stream->distance_count;
 	stream->distance.first = stream->distance_first;
 	stream->distance.pos = stream->distance_pos;

 }

 /* pull 'bits' bits out of the stream. The last bit pulled it returned as the
  * msb. (section 3.1.1)
  */
 static inline unsigned long pull_bits(struct bitstream *stream,
 				      const unsigned int bits)
 {
 	unsigned long ret;
 	int i;

 	ret = 0;
 	for (i = 0; i < bits; i++) {
 		ret += ((*(stream->data) >> stream->bit) & 1) << i;

 		/* if, before incrementing, we are on bit 7,
 		 * go to the lsb of the next byte */
 		if (stream->bit++ == 7) {
 			stream->bit = 0;
 			stream->data++;
 		}
 	}
 	return ret;
 }

 static inline int pull_bit(struct bitstream *stream)
 {
 	int ret = ((*(stream->data) >> stream->bit) & 1);
 	if (stream->bit++ == 7) {
 		stream->bit = 0;
 		stream->data++;
 	}
 	return ret;
 }

 /* discard bits up to the next whole byte */
 static void discard_bits(struct bitstream *stream)
 {
 	if (stream->bit != 0) {
 		stream->bit = 0;
 		stream->data++;
 	}
 }

 /* No decompression, the data is all literals (section 3.2.4) */
 static void decompress_none(struct bitstream *stream, unsigned char *dest)
 {
 	unsigned int length;

 	discard_bits(stream);
 	length = *(stream->data++);
 	length += *(stream->data++) << 8;
 	pull_bits(stream, 16);	/* throw away the inverse of the size */

 	stream->decoded += length;
 	stream->memcpy(dest, stream->data, length);
 	stream->data += length;
 }

 /* Read in a symbol from the stream (section 3.2.2) */
 static int read_symbol(struct bitstream *stream, struct huffman_set *set)
 {
 	int bits = 0;
 	int code = 0;
 	while (!(set->count[bits] && code < set->first[bits] +
 					     set->count[bits])) {
 		code = (code << 1) + pull_bit(stream);
 		if (++bits > set->bits) {
 			/* error decoding (corrupted data?) */
 			stream->error = CODE_NOT_FOUND;
 			return -1;
 		}
 	}
 	return set->symbols[set->pos[bits] + code - set->first[bits]];
 }

 /* decompress a stream of data encoded with the passed length and distance
  * huffman codes */
 static void decompress_huffman(struct bitstream *stream, unsigned char *dest)
 {
 	struct huffman_set *lengths = &(stream->lengths);
 	struct huffman_set *distance = &(stream->distance);

 	int symbol, length, dist, i;

 	do {
 		if ((symbol = read_symbol(stream, lengths)) < 0) return;
 		if (symbol < 256) {
 			*(dest++) = symbol; /* symbol is a literal */
 			stream->decoded++;
 		} else if (symbol > 256) {
 			/* Determine the length of the repitition
 			 * (section 3.2.5) */
 			if (symbol < 265) length = symbol - 254;
 			else if (symbol == 285) length = 258;
 			else {
 				length = pull_bits(stream, (symbol - 261) >> 2);
 				length += (4 << ((symbol - 261) >> 2)) + 3;
 				length += ((symbol - 1) % 4) <<
 					  ((symbol - 261) >> 2);
 			}

 			/* Determine how far back to go */
 			if ((symbol = read_symbol(stream, distance)) < 0)
 				return;
 			if (symbol < 4) dist = symbol + 1;
 			else {
 				dist = pull_bits(stream, (symbol - 2) >> 1);
 				dist += (2 << ((symbol - 2) >> 1)) + 1;
 				dist += (symbol % 2) << ((symbol - 2) >> 1);
 			}
 			stream->decoded += length;
 			for (i = 0; i < length; i++) {
 				*dest = dest[-dist];
 				dest++;
 			}
 		}
 	} while (symbol != 256); /* 256 is the end of the data block */
 }

 /* Fill the lookup tables (section 3.2.2) */
 static void fill_code_tables(struct huffman_set *set)
 {
 	int code = 0, i, length;

 	/* fill in the first code of each bit length, and the pos pointer */
 	set->pos[0] = 0;
 	for (i = 1; i < set->bits; i++) {
 		code = (code + set->count[i - 1]) << 1;
 		set->first[i] = code;
 		set->pos[i] = set->pos[i - 1] + set->count[i - 1];
 	}

 	/* Fill in the table of symbols in order of their huffman code */
 	for (i = 0; i < set->num_symbols; i++) {
 		if ((length = set->lengths[i]))
 			set->symbols[set->pos[length]++] = i;
 	}

 	/* reset the pos pointer */
 	for (i = 1; i < set->bits; i++) set->pos[i] -= set->count[i];
 }

 static void init_code_tables(struct huffman_set *set)
 {
 	cramfs_memset(set->lengths, 0, set->num_symbols);
 	cramfs_memset(set->count, 0, set->bits);
 	cramfs_memset(set->first, 0, set->bits);
 }

 /* read in the huffman codes for dynamic decoding (section 3.2.7) */
 static void decompress_dynamic(struct bitstream *stream, unsigned char *dest)
 {
 	/* I tried my best to minimize the memory footprint here, while still
 	 * keeping up performance. I really dislike the _lengths[] tables, but
 	 * I see no way of eliminating them without a sizable performance
 	 * impact. The first struct table keeps track of stats on each bit
 	 * length. The _length table keeps a record of the bit length of each
 	 * symbol. The _symbols table is for looking up symbols by the huffman
 	 * code (the pos element points to the first place in the symbol table
 	 * where that bit length occurs). I also hate the initization of these
 	 * structs, if someone knows how to compact these, lemme know. */

 	struct huffman_set *codes = &(stream->codes);
 	struct huffman_set *lengths = &(stream->lengths);
 	struct huffman_set *distance = &(stream->distance);

 	int hlit = pull_bits(stream, 5) + 257;
 	int hdist = pull_bits(stream, 5) + 1;
 	int hclen = pull_bits(stream, 4) + 4;
 	int length, curr_code, symbol, i, last_code;

 	last_code = 0;

 	init_code_tables(codes);
 	init_code_tables(lengths);
 	init_code_tables(distance);

 	/* fill in the count of each bit length' as well as the lengths
 	 * table */
 	for (i = 0; i < hclen; i++) {
 		length = pull_bits(stream, 3);
 		codes->lengths[huffman_order[i]] = length;
 		if (length) codes->count[length]++;

 	}
 	fill_code_tables(codes);

 	/* Do the same for the length codes, being carefull of wrap through
 	 * to the distance table */
 	curr_code = 0;
 	while (curr_code < hlit) {
 		if ((symbol = read_symbol(stream, codes)) < 0) return;
 		if (symbol == 0) {
 			curr_code++;
 			last_code = 0;
 		} else if (symbol < 16) { /* Literal length */
 			lengths->lengths[curr_code] =  last_code = symbol;
 			lengths->count[symbol]++;
 			curr_code++;
 		} else if (symbol == 16) { /* repeat the last symbol 3 - 6
 					    * times */
 			length = 3 + pull_bits(stream, 2);
 			for (;length; length--, curr_code++)
 				if (curr_code < hlit) {
 					lengths->lengths[curr_code] =
 						last_code;
 					lengths->count[last_code]++;
 				} else { /* wrap to the distance table */
 					distance->lengths[curr_code - hlit] =
 						last_code;
 					distance->count[last_code]++;
 				}
 		} else if (symbol == 17) { /* repeat a bit length 0 */
 			curr_code += 3 + pull_bits(stream, 3);
 			last_code = 0;
 		} else { /* same, but more times */
 			curr_code += 11 + pull_bits(stream, 7);
 			last_code = 0;
 		}
 	}
 	fill_code_tables(lengths);

 	/* Fill the distance table, don't need to worry about wrapthrough
 	 * here */
 	curr_code -= hlit;
 	while (curr_code < hdist) {
 		if ((symbol = read_symbol(stream, codes)) < 0) return;
 		if (symbol == 0) {
 			curr_code++;
 			last_code = 0;
 		} else if (symbol < 16) {
 			distance->lengths[curr_code] = last_code = symbol;
 			distance->count[symbol]++;
 			curr_code++;
 		} else if (symbol == 16) {
 			length = 3 + pull_bits(stream, 2);
 			for (;length; length--, curr_code++) {
 				distance->lengths[curr_code] =
 					last_code;
 				distance->count[last_code]++;
 			}
 		} else if (symbol == 17) {
 			curr_code += 3 + pull_bits(stream, 3);
 			last_code = 0;
 		} else {
 			curr_code += 11 + pull_bits(stream, 7);
 			last_code = 0;
 		}
 	}
 	fill_code_tables(distance);

 	decompress_huffman(stream, dest);
 }

 /* fill in the length and distance huffman codes for fixed encoding
  * (section 3.2.6) */
 static void decompress_fixed(struct bitstream *stream, unsigned char *dest)
 {
 	/* let gcc fill in the initial values */
 	struct huffman_set *lengths = &(stream->lengths);
 	struct huffman_set *distance = &(stream->distance);

 	cramfs_memset(lengths->count, 0, 16);
 	cramfs_memset(lengths->first, 0, 16);
 	cramfs_memset(lengths->lengths, 8, 144);
 	cramfs_memset(lengths->lengths + 144, 9, 112);
 	cramfs_memset(lengths->lengths + 256, 7, 24);
 	cramfs_memset(lengths->lengths + 280, 8, 8);
 	lengths->count[7] = 24;
 	lengths->count[8] = 152;
 	lengths->count[9] = 112;

 	cramfs_memset(distance->count, 0, 16);
 	cramfs_memset(distance->first, 0, 16);
 	cramfs_memset(distance->lengths, 5, 32);
 	distance->count[5] = 32;

 	fill_code_tables(lengths);
 	fill_code_tables(distance);

 	decompress_huffman(stream, dest);
 }

 /* returns the number of bytes decoded, < 0 if there was an error. Note that
  * this function assumes that the block starts on a byte boundry
  * (non-compliant, but I don't see where this would happen). section 3.2.3 */
 long decompress_block(unsigned char *dest, unsigned char *source,
 		      void *(*inflate_memcpy)(void *, const void *, size))
 {
 	int bfinal, btype;
 	struct bitstream stream;

 	init_stream(&stream, source, inflate_memcpy);
 	do {
 		bfinal = pull_bit(&stream);
 		btype = pull_bits(&stream, 2);
 		if (btype == NO_COMP) decompress_none(&stream, dest + stream.decoded);
 		else if (btype == DYNAMIC_COMP)
 			decompress_dynamic(&stream, dest + stream.decoded);
 		else if (btype == FIXED_COMP) decompress_fixed(&stream, dest + stream.decoded);
 		else stream.error = COMP_UNKNOWN;
 	} while (!bfinal && !stream.error);

 #if 0
 	putstr("decompress_block start\r\n");
 	putLabeledWord("stream.error = ",stream.error);
 	putLabeledWord("stream.decoded = ",stream.decoded);
 	putLabeledWord("dest = ",dest);
 	putstr("decompress_block end\r\n");
 #endif
 	return stream.error ? -stream.error : stream.decoded;
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*-------------------------------------------------------------------------
	* Filename: mini_inflate.c
	* Version: $Id: mini_inflate.c,v 1.3 2002/01/24 22:58:42 rfeany Exp $
	* Copyright: Copyright (C) 2001, Russ Dill
	* Author: Russ Dill <Russ.Dill@asu.edu>
	* Description: Mini inflate implementation (RFC 1951)
	-----------------------------------------------------------------------/

	#include <config.h>
	#include <jffs2/mini_inflate.h>

	/* The order that the code lengths in section 3.2.7 are in */
	static unsigned char huffman_order[] = {16, 17, 18, 0, 8, 7, 9, 6, 10, 5,
	11, 4, 12, 3, 13, 2, 14, 1, 15};

	static inline void cramfs_memset(int *s, const int c, size n)
	{
	n--;
	for (;n > 0; n--) s[n] = c;
	s[0] = c;
	}

	/* associate a stream with a block of data and reset the stream */
	static void init_stream(struct bitstream stream, unsigned char data,
	void (inflate_memcpy)(void , const void , size))
	{
	stream->error = NO_ERROR;
	stream->memcpy = inflate_memcpy;
	stream->decoded = 0;
	stream->data = data;
	stream->bit = 0; /* The first bit of the stream is the lsb of the
	* first byte */

	/* really sorry about all this initialization, think of a better way,
	* let me know and it will get cleaned up */
	stream->codes.bits = 8;
	stream->codes.num_symbols = 19;
	stream->codes.lengths = stream->code_lengths;
	stream->codes.symbols = stream->code_symbols;
	stream->codes.count = stream->code_count;
	stream->codes.first = stream->code_first;
	stream->codes.pos = stream->code_pos;

	stream->lengths.bits = 16;
	stream->lengths.num_symbols = 288;
	stream->lengths.lengths = stream->length_lengths;
	stream->lengths.symbols = stream->length_symbols;
	stream->lengths.count = stream->length_count;
	stream->lengths.first = stream->length_first;
	stream->lengths.pos = stream->length_pos;

	stream->distance.bits = 16;
	stream->distance.num_symbols = 32;
	stream->distance.lengths = stream->distance_lengths;
	stream->distance.symbols = stream->distance_symbols;
	stream->distance.count = stream->distance_count;
	stream->distance.first = stream->distance_first;
	stream->distance.pos = stream->distance_pos;

	}

	/* pull 'bits' bits out of the stream. The last bit pulled it returned as the
	* msb. (section 3.1.1)
	*/
	static inline unsigned long pull_bits(struct bitstream *stream,
	const unsigned int bits)
	{
	unsigned long ret;
	int i;

	ret = 0;
	for (i = 0; i < bits; i++) {
	ret += ((*(stream->data) >> stream->bit) & 1) << i;

	/* if, before incrementing, we are on bit 7,
	* go to the lsb of the next byte */
	if (stream->bit++ == 7) {
	stream->bit = 0;
	stream->data++;
	}
	}
	return ret;
	}

	static inline int pull_bit(struct bitstream *stream)
	{
	int ret = ((*(stream->data) >> stream->bit) & 1);
	if (stream->bit++ == 7) {
	stream->bit = 0;
	stream->data++;
	}
	return ret;
	}

	/* discard bits up to the next whole byte */
	static void discard_bits(struct bitstream *stream)
	{
	if (stream->bit != 0) {
	stream->bit = 0;
	stream->data++;
	}
	}

	/* No decompression, the data is all literals (section 3.2.4) */
	static void decompress_none(struct bitstream stream, unsigned char dest)
	{
	unsigned int length;

	discard_bits(stream);
	length = *(stream->data++);
	length += *(stream->data++) << 8;
	pull_bits(stream, 16); /* throw away the inverse of the size */

	stream->decoded += length;
	stream->memcpy(dest, stream->data, length);
	stream->data += length;
	}

	/* Read in a symbol from the stream (section 3.2.2) */
	static int read_symbol(struct bitstream stream, struct huffman_set set)
	{
	int bits = 0;
	int code = 0;
	while (!(set->count[bits] && code < set->first[bits] +
	set->count[bits])) {
	code = (code << 1) + pull_bit(stream);
	if (++bits > set->bits) {
	/* error decoding (corrupted data?) */
	stream->error = CODE_NOT_FOUND;
	return -1;
	}
	}
	return set->symbols[set->pos[bits] + code - set->first[bits]];
	}

	/* decompress a stream of data encoded with the passed length and distance
	* huffman codes */
	static void decompress_huffman(struct bitstream stream, unsigned char dest)
	{
	struct huffman_set *lengths = &(stream->lengths);
	struct huffman_set *distance = &(stream->distance);

	int symbol, length, dist, i;

	do {
	if ((symbol = read_symbol(stream, lengths)) < 0) return;
	if (symbol < 256) {
	(dest++) = symbol; / symbol is a literal */
	stream->decoded++;
	} else if (symbol > 256) {
	/* Determine the length of the repitition
	* (section 3.2.5) */
	if (symbol < 265) length = symbol - 254;
	else if (symbol == 285) length = 258;
	else {
	length = pull_bits(stream, (symbol - 261) >> 2);
	length += (4 << ((symbol - 261) >> 2)) + 3;
	length += ((symbol - 1) % 4) <<
	((symbol - 261) >> 2);
	}

	/* Determine how far back to go */
	if ((symbol = read_symbol(stream, distance)) < 0)
	return;
	if (symbol < 4) dist = symbol + 1;
	else {
	dist = pull_bits(stream, (symbol - 2) >> 1);
	dist += (2 << ((symbol - 2) >> 1)) + 1;
	dist += (symbol % 2) << ((symbol - 2) >> 1);
	}
	stream->decoded += length;
	for (i = 0; i < length; i++) {
	*dest = dest[-dist];
	dest++;
	}
	}
	} while (symbol != 256); /* 256 is the end of the data block */
	}

	/* Fill the lookup tables (section 3.2.2) */
	static void fill_code_tables(struct huffman_set *set)
	{
	int code = 0, i, length;

	/* fill in the first code of each bit length, and the pos pointer */
	set->pos[0] = 0;
	for (i = 1; i < set->bits; i++) {
	code = (code + set->count[i - 1]) << 1;
	set->first[i] = code;
	set->pos[i] = set->pos[i - 1] + set->count[i - 1];
	}

	/* Fill in the table of symbols in order of their huffman code */
	for (i = 0; i < set->num_symbols; i++) {
	if ((length = set->lengths[i]))
	set->symbols[set->pos[length]++] = i;
	}

	/* reset the pos pointer */
	for (i = 1; i < set->bits; i++) set->pos[i] -= set->count[i];
	}

	static void init_code_tables(struct huffman_set *set)
	{
	cramfs_memset(set->lengths, 0, set->num_symbols);
	cramfs_memset(set->count, 0, set->bits);
	cramfs_memset(set->first, 0, set->bits);
	}

	/* read in the huffman codes for dynamic decoding (section 3.2.7) */
	static void decompress_dynamic(struct bitstream stream, unsigned char dest)
	{
	/* I tried my best to minimize the memory footprint here, while still
	* keeping up performance. I really dislike the _lengths[] tables, but
	* I see no way of eliminating them without a sizable performance
	* impact. The first struct table keeps track of stats on each bit
	* length. The _length table keeps a record of the bit length of each
	* symbol. The _symbols table is for looking up symbols by the huffman
	* code (the pos element points to the first place in the symbol table
	* where that bit length occurs). I also hate the initization of these
	* structs, if someone knows how to compact these, lemme know. */

	struct huffman_set *codes = &(stream->codes);
	struct huffman_set *lengths = &(stream->lengths);
	struct huffman_set *distance = &(stream->distance);

	int hlit = pull_bits(stream, 5) + 257;
	int hdist = pull_bits(stream, 5) + 1;
	int hclen = pull_bits(stream, 4) + 4;
	int length, curr_code, symbol, i, last_code;

	last_code = 0;

	init_code_tables(codes);
	init_code_tables(lengths);
	init_code_tables(distance);

	/* fill in the count of each bit length' as well as the lengths
	* table */
	for (i = 0; i < hclen; i++) {
	length = pull_bits(stream, 3);
	codes->lengths[huffman_order[i]] = length;
	if (length) codes->count[length]++;

	}
	fill_code_tables(codes);

	/* Do the same for the length codes, being carefull of wrap through
	* to the distance table */
	curr_code = 0;
	while (curr_code < hlit) {
	if ((symbol = read_symbol(stream, codes)) < 0) return;
	if (symbol == 0) {
	curr_code++;
	last_code = 0;
	} else if (symbol < 16) { /* Literal length */
	lengths->lengths[curr_code] = last_code = symbol;
	lengths->count[symbol]++;
	curr_code++;
	} else if (symbol == 16) { /* repeat the last symbol 3 - 6
	* times */
	length = 3 + pull_bits(stream, 2);
	for (;length; length--, curr_code++)
	if (curr_code < hlit) {
	lengths->lengths[curr_code] =
	last_code;
	lengths->count[last_code]++;
	} else { /* wrap to the distance table */
	distance->lengths[curr_code - hlit] =
	last_code;
	distance->count[last_code]++;
	}
	} else if (symbol == 17) { /* repeat a bit length 0 */
	curr_code += 3 + pull_bits(stream, 3);
	last_code = 0;
	} else { /* same, but more times */
	curr_code += 11 + pull_bits(stream, 7);
	last_code = 0;
	}
	}
	fill_code_tables(lengths);

	/* Fill the distance table, don't need to worry about wrapthrough
	* here */
	curr_code -= hlit;
	while (curr_code < hdist) {
	if ((symbol = read_symbol(stream, codes)) < 0) return;
	if (symbol == 0) {
	curr_code++;
	last_code = 0;
	} else if (symbol < 16) {
	distance->lengths[curr_code] = last_code = symbol;
	distance->count[symbol]++;
	curr_code++;
	} else if (symbol == 16) {
	length = 3 + pull_bits(stream, 2);
	for (;length; length--, curr_code++) {
	distance->lengths[curr_code] =
	last_code;
	distance->count[last_code]++;
	}
	} else if (symbol == 17) {
	curr_code += 3 + pull_bits(stream, 3);
	last_code = 0;
	} else {
	curr_code += 11 + pull_bits(stream, 7);
	last_code = 0;
	}
	}
	fill_code_tables(distance);

	decompress_huffman(stream, dest);
	}

	/* fill in the length and distance huffman codes for fixed encoding
	* (section 3.2.6) */
	static void decompress_fixed(struct bitstream stream, unsigned char dest)
	{
	/* let gcc fill in the initial values */
	struct huffman_set *lengths = &(stream->lengths);
	struct huffman_set *distance = &(stream->distance);

	cramfs_memset(lengths->count, 0, 16);
	cramfs_memset(lengths->first, 0, 16);
	cramfs_memset(lengths->lengths, 8, 144);
	cramfs_memset(lengths->lengths + 144, 9, 112);
	cramfs_memset(lengths->lengths + 256, 7, 24);
	cramfs_memset(lengths->lengths + 280, 8, 8);
	lengths->count[7] = 24;
	lengths->count[8] = 152;
	lengths->count[9] = 112;

	cramfs_memset(distance->count, 0, 16);
	cramfs_memset(distance->first, 0, 16);
	cramfs_memset(distance->lengths, 5, 32);
	distance->count[5] = 32;

	fill_code_tables(lengths);
	fill_code_tables(distance);

	decompress_huffman(stream, dest);
	}

	/* returns the number of bytes decoded, < 0 if there was an error. Note that
	* this function assumes that the block starts on a byte boundry
	* (non-compliant, but I don't see where this would happen). section 3.2.3 */
	long decompress_block(unsigned char dest, unsigned char source,
	void (inflate_memcpy)(void , const void , size))
	{
	int bfinal, btype;
	struct bitstream stream;

	init_stream(&stream, source, inflate_memcpy);
	do {
	bfinal = pull_bit(&stream);
	btype = pull_bits(&stream, 2);
	if (btype == NO_COMP) decompress_none(&stream, dest + stream.decoded);
	else if (btype == DYNAMIC_COMP)
	decompress_dynamic(&stream, dest + stream.decoded);
	else if (btype == FIXED_COMP) decompress_fixed(&stream, dest + stream.decoded);
	else stream.error = COMP_UNKNOWN;
	} while (!bfinal && !stream.error);

	#if 0
	putstr("decompress_block start\r\n");
	putLabeledWord("stream.error = ",stream.error);
	putLabeledWord("stream.decoded = ",stream.decoded);
	putLabeledWord("dest = ",dest);
	putstr("decompress_block end\r\n");
	#endif
	return stream.error ? -stream.error : stream.decoded;
	}