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109 lines
3.0 KiB
C
109 lines
3.0 KiB
C
#ifndef _HUFFMAN_H
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#define _HUFFMAN_H
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/*
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* Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*/
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/**
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* @file
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*
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* Huffman alphabets
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*
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*/
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/** Maximum length of a Huffman symbol (in bits) */
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#define HUFFMAN_BITS 16
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/** Raw huffman symbol */
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typedef uint16_t huffman_raw_symbol_t;
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/** Quick lookup length for a Huffman symbol (in bits)
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*
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* This is a policy decision.
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*/
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#define HUFFMAN_QL_BITS 7
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/** Quick lookup shift */
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#define HUFFMAN_QL_SHIFT ( HUFFMAN_BITS - HUFFMAN_QL_BITS )
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/** A Huffman-coded set of symbols of a given length */
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struct huffman_symbols {
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/** Length of Huffman-coded symbols (in bits) */
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uint8_t bits;
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/** Shift to normalise symbols of this length to HUFFMAN_BITS bits */
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uint8_t shift;
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/** Number of Huffman-coded symbols having this length */
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uint16_t freq;
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/** First symbol of this length (normalised to HUFFMAN_BITS bits)
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*
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* Stored as a 32-bit value to allow the value
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* (1<<HUFFMAN_BITS ) to be used for empty sets of symbols
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* longer than the maximum utilised length.
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*/
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uint32_t start;
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/** Raw symbols having this length */
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huffman_raw_symbol_t *raw;
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};
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/** A Huffman-coded alphabet */
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struct huffman_alphabet {
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/** Huffman-coded symbol set for each length */
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struct huffman_symbols huf[HUFFMAN_BITS];
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/** Quick lookup table */
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uint8_t lookup[ 1 << HUFFMAN_QL_BITS ];
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/** Raw symbols
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*
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* Ordered by Huffman-coded symbol length, then by symbol
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* value. This field has a variable length.
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*/
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huffman_raw_symbol_t raw[0];
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};
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/**
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* Get Huffman symbol length
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*
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* @v sym Huffman symbol set
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* @ret len Length (in bits)
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*/
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static inline __attribute__ (( always_inline )) unsigned int
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huffman_len ( struct huffman_symbols *sym ) {
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return sym->bits;
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}
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/**
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* Get Huffman symbol value
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*
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* @v sym Huffman symbol set
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* @v huf Raw input value (normalised to HUFFMAN_BITS bits)
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* @ret raw Raw symbol value
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*/
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static inline __attribute__ (( always_inline )) huffman_raw_symbol_t
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huffman_raw ( struct huffman_symbols *sym, unsigned int huf ) {
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return sym->raw[ huf >> sym->shift ];
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}
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extern int huffman_alphabet ( struct huffman_alphabet *alphabet,
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uint8_t *lengths, unsigned int count );
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extern struct huffman_symbols *
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huffman_sym ( struct huffman_alphabet *alphabet, unsigned int huf );
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#endif /* _HUFFMAN_H */
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