520274219a
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@13562 a1c6a512-1295-4272-9138-f99709370657
180 lines
4.7 KiB
C
180 lines
4.7 KiB
C
/*
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libdemac - A Monkey's Audio decoder
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$Id:$
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Copyright (C) Dave Chapman 2007
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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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 St, Fifth Floor, Boston, MA 02110, USA
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*/
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/*
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Range decoder adapted from rangecod.c included in:
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http://www.compressconsult.com/rangecoder/rngcod13.zip
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rangecod.c range encoding
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(c) Michael Schindler
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1997, 1998, 1999, 2000
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http://www.compressconsult.com/
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michael@compressconsult.com
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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The encoding functions were removed, and functions turned into "static
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inline" functions and moved to a .h file. Some minor cosmetic changes
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were made (e.g. turning pre-processor symbols into upper-case,
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removing the rc parameter from each function (and the RNGC macro)).
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*/
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/* BITSTREAM READING FUNCTIONS */
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/* We deal with the input data one byte at a time - to ensure
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functionality on CPUs of any endianness regardless of any requirements
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for aligned reads.
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*/
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static unsigned char* bytebuffer IBSS_ATTR;
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static int bytebufferoffset IBSS_ATTR;
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static inline void skip_byte(void)
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{
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if (bytebufferoffset) {
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bytebufferoffset--;
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} else {
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bytebufferoffset = 3;
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bytebuffer += 4;
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}
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}
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static inline int read_byte(void)
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{
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int ch = bytebuffer[bytebufferoffset];
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skip_byte();
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return ch;
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}
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/* RANGE DECODING FUNCTIONS */
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/* SIZE OF RANGE ENCODING CODE VALUES. */
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#define CODE_BITS 32
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#define TOP_VALUE ((unsigned int)1 << (CODE_BITS-1))
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#define SHIFT_BITS (CODE_BITS - 9)
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#define EXTRA_BITS ((CODE_BITS-2) % 8 + 1)
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#define BOTTOM_VALUE (TOP_VALUE >> 8)
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struct rangecoder_t
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{
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uint32_t low; /* low end of interval */
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uint32_t range; /* length of interval */
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uint32_t help; /* bytes_to_follow resp. intermediate value */
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unsigned int buffer; /* buffer for input/output */
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};
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static struct rangecoder_t rc;
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/* Start the decoder */
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static inline void range_start_decoding(void)
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{
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rc.buffer = read_byte();
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rc.low = rc.buffer >> (8 - EXTRA_BITS);
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rc.range = (uint32_t) 1 << EXTRA_BITS;
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}
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static inline void range_dec_normalize(void)
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{
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while (rc.range <= BOTTOM_VALUE)
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{
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rc.buffer = (rc.buffer << 8) | read_byte();
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rc.low = (rc.low << 8) | ((rc.buffer >> 1) & 0xff);
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rc.range <<= 8;
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}
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}
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/* Calculate culmulative frequency for next symbol. Does NO update!*/
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/* tot_f is the total frequency */
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/* or: totf is (code_value)1<<shift */
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/* returns the culmulative frequency */
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static inline int range_decode_culfreq(int tot_f)
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{ int tmp;
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range_dec_normalize();
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rc.help = rc.range / tot_f;
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tmp = rc.low / rc.help;
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return tmp;
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}
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static inline int range_decode_culshift(int shift)
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{
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int tmp;
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range_dec_normalize();
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rc.help = rc.range>>shift;
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tmp = rc.low/rc.help;
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return tmp;
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}
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/* Update decoding state */
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/* sy_f is the interval length (frequency of the symbol) */
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/* lt_f is the lower end (frequency sum of < symbols) */
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static inline void range_decode_update(int sy_f, int lt_f)
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{ int tmp;
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tmp = rc.help * lt_f;
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rc.low -= tmp;
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rc.range = rc.help * sy_f;
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}
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/* Decode a byte/short without modelling */
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static inline unsigned char decode_byte(void)
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{ int tmp = range_decode_culshift(8);
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range_decode_update( 1,tmp);
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return tmp;
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}
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static inline int short range_decode_short(void)
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{ int tmp = range_decode_culshift(16);
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range_decode_update( 1,tmp);
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return tmp;
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}
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/* Decode n bits (n <= 16) without modelling - based on range_decode_short */
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static inline int range_decode_bits(int n)
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{ int tmp = range_decode_culshift(n);
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range_decode_update( 1,tmp);
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return tmp;
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}
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/* Finish decoding */
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static inline void range_done_decoding(void)
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{ range_dec_normalize(); /* normalize to use up all bytes */
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}
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