173 lines
6.3 KiB
C
173 lines
6.3 KiB
C
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/* This file is part of libmspack.
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* (C) 2003-2014 Stuart Caie.
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*
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* libmspack is free software; you can redistribute it and/or modify it under
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* the terms of the GNU Lesser General Public License (LGPL) version 2.1
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*
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* For further details, see the file COPYING.LIB distributed with libmspack
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*/
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#ifndef MSPACK_READHUFF_H
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#define MSPACK_READHUFF_H 1
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/* This implements a fast Huffman tree decoding system. */
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#if !(defined(BITS_ORDER_MSB) || defined(BITS_ORDER_LSB))
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# error "readhuff.h is used in conjunction with readbits.h, include that first"
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#endif
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#if !(defined(TABLEBITS) && defined(MAXSYMBOLS))
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# error "define TABLEBITS(tbl) and MAXSYMBOLS(tbl) before using readhuff.h"
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#endif
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#if !(defined(HUFF_TABLE) && defined(HUFF_LEN))
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# error "define HUFF_TABLE(tbl) and HUFF_LEN(tbl) before using readhuff.h"
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#endif
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#ifndef HUFF_ERROR
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# error "define HUFF_ERROR before using readhuff.h"
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#endif
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#ifndef HUFF_MAXBITS
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# define HUFF_MAXBITS 16
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#endif
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/* Decodes the next huffman symbol from the input bitstream into var.
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* Do not use this macro on a table unless build_decode_table() succeeded.
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*/
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#define READ_HUFFSYM(tbl, var) do { \
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ENSURE_BITS(HUFF_MAXBITS); \
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sym = HUFF_TABLE(tbl, PEEK_BITS(TABLEBITS(tbl))); \
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if (sym >= MAXSYMBOLS(tbl)) HUFF_TRAVERSE(tbl); \
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(var) = sym; \
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i = HUFF_LEN(tbl, sym); \
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REMOVE_BITS(i); \
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} while (0)
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#ifdef BITS_ORDER_LSB
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# define HUFF_TRAVERSE(tbl) do { \
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i = TABLEBITS(tbl) - 1; \
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do { \
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if (i++ > HUFF_MAXBITS) HUFF_ERROR; \
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sym = HUFF_TABLE(tbl, \
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(sym << 1) | ((bit_buffer >> i) & 1)); \
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} while (sym >= MAXSYMBOLS(tbl)); \
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} while (0)
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#else
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#define HUFF_TRAVERSE(tbl) do { \
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i = 1 << (BITBUF_WIDTH - TABLEBITS(tbl)); \
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do { \
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if ((i >>= 1) == 0) HUFF_ERROR; \
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sym = HUFF_TABLE(tbl, \
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(sym << 1) | ((bit_buffer & i) ? 1 : 0)); \
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} while (sym >= MAXSYMBOLS(tbl)); \
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} while (0)
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#endif
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/* make_decode_table(nsyms, nbits, length[], table[])
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*
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* This function was originally coded by David Tritscher.
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* It builds a fast huffman decoding table from
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* a canonical huffman code lengths table.
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*
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* nsyms = total number of symbols in this huffman tree.
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* nbits = any symbols with a code length of nbits or less can be decoded
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* in one lookup of the table.
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* length = A table to get code lengths from [0 to nsyms-1]
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* table = The table to fill up with decoded symbols and pointers.
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* Should be ((1<<nbits) + (nsyms*2)) in length.
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*
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* Returns 0 for OK or 1 for error
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*/
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static int make_decode_table(unsigned int nsyms, unsigned int nbits,
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unsigned char *length, unsigned short *table)
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{
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register unsigned short sym, next_symbol;
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register unsigned int leaf, fill;
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#ifdef BITS_ORDER_LSB
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register unsigned int reverse;
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#endif
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register unsigned char bit_num;
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unsigned int pos = 0; /* the current position in the decode table */
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unsigned int table_mask = 1 << nbits;
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unsigned int bit_mask = table_mask >> 1; /* don't do 0 length codes */
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/* fill entries for codes short enough for a direct mapping */
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for (bit_num = 1; bit_num <= nbits; bit_num++) {
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for (sym = 0; sym < nsyms; sym++) {
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if (length[sym] != bit_num) continue;
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#ifdef BITS_ORDER_MSB
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leaf = pos;
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#else
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/* reverse the significant bits */
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fill = length[sym]; reverse = pos >> (nbits - fill); leaf = 0;
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do {leaf <<= 1; leaf |= reverse & 1; reverse >>= 1;} while (--fill);
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#endif
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if((pos += bit_mask) > table_mask) return 1; /* table overrun */
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/* fill all possible lookups of this symbol with the symbol itself */
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#ifdef BITS_ORDER_MSB
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for (fill = bit_mask; fill-- > 0;) table[leaf++] = sym;
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#else
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fill = bit_mask; next_symbol = 1 << bit_num;
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do { table[leaf] = sym; leaf += next_symbol; } while (--fill);
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#endif
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}
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bit_mask >>= 1;
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}
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/* exit with success if table is now complete */
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if (pos == table_mask) return 0;
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/* mark all remaining table entries as unused */
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for (sym = pos; sym < table_mask; sym++) {
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#ifdef BITS_ORDER_MSB
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table[sym] = 0xFFFF;
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#else
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reverse = sym; leaf = 0; fill = nbits;
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do { leaf <<= 1; leaf |= reverse & 1; reverse >>= 1; } while (--fill);
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table[leaf] = 0xFFFF;
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#endif
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}
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/* next_symbol = base of allocation for long codes */
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next_symbol = ((table_mask >> 1) < nsyms) ? nsyms : (table_mask >> 1);
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/* give ourselves room for codes to grow by up to 16 more bits.
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* codes now start at bit nbits+16 and end at (nbits+16-codelength) */
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pos <<= 16;
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table_mask <<= 16;
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bit_mask = 1 << 15;
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for (bit_num = nbits+1; bit_num <= HUFF_MAXBITS; bit_num++) {
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for (sym = 0; sym < nsyms; sym++) {
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if (length[sym] != bit_num) continue;
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if (pos >= table_mask) return 1; /* table overflow */
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#ifdef BITS_ORDER_MSB
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leaf = pos >> 16;
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#else
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/* leaf = the first nbits of the code, reversed */
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reverse = pos >> 16; leaf = 0; fill = nbits;
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do {leaf <<= 1; leaf |= reverse & 1; reverse >>= 1;} while (--fill);
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#endif
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for (fill = 0; fill < (bit_num - nbits); fill++) {
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/* if this path hasn't been taken yet, 'allocate' two entries */
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if (table[leaf] == 0xFFFF) {
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table[(next_symbol << 1) ] = 0xFFFF;
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table[(next_symbol << 1) + 1 ] = 0xFFFF;
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table[leaf] = next_symbol++;
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}
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/* follow the path and select either left or right for next bit */
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leaf = table[leaf] << 1;
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if ((pos >> (15-fill)) & 1) leaf++;
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}
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table[leaf] = sym;
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pos += bit_mask;
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}
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bit_mask >>= 1;
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}
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/* full table? */
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return (pos == table_mask) ? 0 : 1;
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}
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#endif
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