/src/opus/celt/entdec.c

Source
/* Copyright (c) 2001-2011 Timothy B. Terriberry
   Copyright (c) 2008-2009 Xiph.Org Foundation */
/*
   Redistribution and use in source and binary forms, with or without
   modification, are permitted provided that the following conditions
   are met:

   - Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.

   - Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
   OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stddef.h>
#include "os_support.h"
#include "arch.h"
#include "entdec.h"
#include "mfrngcod.h"

/*A range decoder.
  This is an entropy decoder based upon \cite{Mar79}, which is itself a
   rediscovery of the FIFO arithmetic code introduced by \cite{Pas76}.
  It is very similar to arithmetic encoding, except that encoding is done with
   digits in any base, instead of with bits, and so it is faster when using
   larger bases (i.e.: a byte).
  The author claims an average waste of $\frac{1}{2}\log_b(2b)$ bits, where $b$
   is the base, longer than the theoretical optimum, but to my knowledge there
   is no published justification for this claim.
  This only seems true when using near-infinite precision arithmetic so that
   the process is carried out with no rounding errors.

  An excellent description of implementation details is available at
   http://www.arturocampos.com/ac_range.html
  A recent work \cite{MNW98} which proposes several changes to arithmetic
   encoding for efficiency actually re-discovers many of the principles
   behind range encoding, and presents a good theoretical analysis of them.

  End of stream is handled by writing out the smallest number of bits that
   ensures that the stream will be correctly decoded regardless of the value of
   any subsequent bits.
  ec_tell() can be used to determine how many bits were needed to decode
   all the symbols thus far; other data can be packed in the remaining bits of
   the input buffer.
  @PHDTHESIS{Pas76,
    author="Richard Clark Pasco",
    title="Source coding algorithms for fast data compression",
    school="Dept. of Electrical Engineering, Stanford University",
    address="Stanford, CA",
    month=May,
    year=1976
  }
  @INPROCEEDINGS{Mar79,
   author="Martin, G.N.N.",
   title="Range encoding: an algorithm for removing redundancy from a digitised
    message",
   booktitle="Video & Data Recording Conference",
   year=1979,
   address="Southampton",
   month=Jul
  }
  @ARTICLE{MNW98,
   author="Alistair Moffat and Radford Neal and Ian H. Witten",
   title="Arithmetic Coding Revisited",
   journal="{ACM} Transactions on Information Systems",
   year=1998,
   volume=16,
   number=3,
   pages="256--294",
   month=Jul,
   URL="http://www.stanford.edu/class/ee398a/handouts/papers/Moffat98ArithmCoding.pdf"
  }*/

static int ec_read_byte(ec_dec *_this){
  return _this->offs<_this->storage?_this->buf[_this->offs++]:0;
}

static int ec_read_byte_from_end(ec_dec *_this){
  return _this->end_offs<_this->storage?
   _this->buf[_this->storage-++(_this->end_offs)]:0;
}

/*Normalizes the contents of val and rng so that rng lies entirely in the
   high-order symbol.*/
static void ec_dec_normalize(ec_dec *_this){
  /*If the range is too small, rescale it and input some bits.*/
  while(_this->rng<=EC_CODE_BOT){
    int sym;
    _this->nbits_total+=EC_SYM_BITS;
    _this->rng<<=EC_SYM_BITS;
    /*Use up the remaining bits from our last symbol.*/
    sym=_this->rem;
    /*Read the next value from the input.*/
    _this->rem=ec_read_byte(_this);
    /*Take the rest of the bits we need from this new symbol.*/
    sym=(sym<<EC_SYM_BITS|_this->rem)>>(EC_SYM_BITS-EC_CODE_EXTRA);
    /*And subtract them from val, capped to be less than EC_CODE_TOP.*/
    _this->val=((_this->val<<EC_SYM_BITS)+(EC_SYM_MAX&~sym))&(EC_CODE_TOP-1);
  }
}

void ec_dec_init(ec_dec *_this,unsigned char *_buf,opus_uint32 _storage){
  _this->buf=_buf;
  _this->storage=_storage;
  _this->end_offs=0;
  _this->end_window=0;
  _this->nend_bits=0;
  /*This is the offset from which ec_tell() will subtract partial bits.
    The final value after the ec_dec_normalize() call will be the same as in
     the encoder, but we have to compensate for the bits that are added there.*/
  _this->nbits_total=EC_CODE_BITS+1
   -((EC_CODE_BITS-EC_CODE_EXTRA)/EC_SYM_BITS)*EC_SYM_BITS;
  _this->offs=0;
  _this->rng=1U<<EC_CODE_EXTRA;
  _this->rem=ec_read_byte(_this);
  _this->val=_this->rng-1-(_this->rem>>(EC_SYM_BITS-EC_CODE_EXTRA));
  _this->error=0;
  /*Normalize the interval.*/
  ec_dec_normalize(_this);
}

unsigned ec_decode(ec_dec *_this,unsigned _ft){
  unsigned s;
  _this->ext=celt_udiv(_this->rng,_ft);
  s=(unsigned)(_this->val/_this->ext);
  return _ft-EC_MINI(s+1,_ft);
}

unsigned ec_decode_bin(ec_dec *_this,unsigned _bits){
   unsigned s;
   _this->ext=_this->rng>>_bits;
   s=(unsigned)(_this->val/_this->ext);
   return (1U<<_bits)-EC_MINI(s+1U,1U<<_bits);
}

void ec_dec_update(ec_dec *_this,unsigned _fl,unsigned _fh,unsigned _ft){
  opus_uint32 s;
  s=IMUL32(_this->ext,_ft-_fh);
  _this->val-=s;
  _this->rng=_fl>0?IMUL32(_this->ext,_fh-_fl):_this->rng-s;
  ec_dec_normalize(_this);
}

/*The probability of having a "one" is 1/(1<<_logp).*/
int ec_dec_bit_logp(ec_dec *_this,unsigned _logp){
  opus_uint32 r;
  opus_uint32 d;
  opus_uint32 s;
  int         ret;
  r=_this->rng;
  d=_this->val;
  s=r>>_logp;
  ret=d<s;
  if(!ret)_this->val=d-s;
  _this->rng=ret?s:r-s;
  ec_dec_normalize(_this);
  return ret;
}

int ec_dec_icdf(ec_dec *_this,const unsigned char *_icdf,unsigned _ftb){
  opus_uint32 r;
  opus_uint32 d;
  opus_uint32 s;
  opus_uint32 t;
  int         ret;
  s=_this->rng;
  d=_this->val;
  r=s>>_ftb;
  ret=-1;
  do{
    t=s;
    s=IMUL32(r,_icdf[++ret]);
  }
  while(d<s);
  _this->val=d-s;
  _this->rng=t-s;
  ec_dec_normalize(_this);
  return ret;
}

int ec_dec_icdf16(ec_dec *_this,const opus_uint16 *_icdf,unsigned _ftb){
  opus_uint32 r;
  opus_uint32 d;
  opus_uint32 s;
  opus_uint32 t;
  int         ret;
  s=_this->rng;
  d=_this->val;
  r=s>>_ftb;
  ret=-1;
  do{
    t=s;
    s=IMUL32(r,_icdf[++ret]);
  }
  while(d<s);
  _this->val=d-s;
  _this->rng=t-s;
  ec_dec_normalize(_this);
  return ret;
}

opus_uint32 ec_dec_uint(ec_dec *_this,opus_uint32 _ft){
  unsigned ft;
  unsigned s;
  int      ftb;
  /*In order to optimize EC_ILOG(), it is undefined for the value 0.*/
  celt_assert(_ft>1);
  _ft--;
  ftb=EC_ILOG(_ft);
  if(ftb>EC_UINT_BITS){
    opus_uint32 t;
    ftb-=EC_UINT_BITS;
    ft=(unsigned)(_ft>>ftb)+1;
    s=ec_decode(_this,ft);
    ec_dec_update(_this,s,s+1,ft);
    t=(opus_uint32)s<<ftb|ec_dec_bits(_this,ftb);
    if(t<=_ft)return t;
    _this->error=1;
    return _ft;
  }
  else{
    _ft++;
    s=ec_decode(_this,(unsigned)_ft);
    ec_dec_update(_this,s,s+1,(unsigned)_ft);
    return s;
  }
}

opus_uint32 ec_dec_bits(ec_dec *_this,unsigned _bits){
  ec_window   window;
  int         available;
  opus_uint32 ret;
  window=_this->end_window;
  available=_this->nend_bits;
  if((unsigned)available<_bits){
    do{
      window|=(ec_window)ec_read_byte_from_end(_this)<<available;
      available+=EC_SYM_BITS;
    }
    while(available<=EC_WINDOW_SIZE-EC_SYM_BITS);
  }
  ret=(opus_uint32)window&(((opus_uint32)1<<_bits)-1U);
  window>>=_bits;
  available-=_bits;
  _this->end_window=window;
  _this->nend_bits=available;
  _this->nbits_total+=_bits;
  return ret;
}

Coverage Report

Created: 2026-09-28 07:55

Line	Count	Source
1		/* Copyright (c) 2001-2011 Timothy B. Terriberry
2		Copyright (c) 2008-2009 Xiph.Org Foundation */
3		/*
4		Redistribution and use in source and binary forms, with or without
5		modification, are permitted provided that the following conditions
6		are met:
7
8		- Redistributions of source code must retain the above copyright
9		notice, this list of conditions and the following disclaimer.
10
11		- Redistributions in binary form must reproduce the above copyright
12		notice, this list of conditions and the following disclaimer in the
13		documentation and/or other materials provided with the distribution.
14
15		THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16		``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17		LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
18		A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
19		OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
20		EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
21		PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
22		PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
23		LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
24		NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
25		SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26		*/
27
28		#ifdef HAVE_CONFIG_H
29		#include "config.h"
30		#endif
31
32		#include <stddef.h>
33		#include "os_support.h"
34		#include "arch.h"
35		#include "entdec.h"
36		#include "mfrngcod.h"
37
38		/*A range decoder.
39		This is an entropy decoder based upon \cite{Mar79}, which is itself a
40		rediscovery of the FIFO arithmetic code introduced by \cite{Pas76}.
41		It is very similar to arithmetic encoding, except that encoding is done with
42		digits in any base, instead of with bits, and so it is faster when using
43		larger bases (i.e.: a byte).
44		The author claims an average waste of $\frac{1}{2}\log_b(2b)$ bits, where $b$
45		is the base, longer than the theoretical optimum, but to my knowledge there
46		is no published justification for this claim.
47		This only seems true when using near-infinite precision arithmetic so that
48		the process is carried out with no rounding errors.
49
50		An excellent description of implementation details is available at
51		http://www.arturocampos.com/ac_range.html
52		A recent work \cite{MNW98} which proposes several changes to arithmetic
53		encoding for efficiency actually re-discovers many of the principles
54		behind range encoding, and presents a good theoretical analysis of them.
55
56		End of stream is handled by writing out the smallest number of bits that
57		ensures that the stream will be correctly decoded regardless of the value of
58		any subsequent bits.
59		ec_tell() can be used to determine how many bits were needed to decode
60		all the symbols thus far; other data can be packed in the remaining bits of
61		the input buffer.
62		@PHDTHESIS{Pas76,
63		author="Richard Clark Pasco",
64		title="Source coding algorithms for fast data compression",
65		school="Dept. of Electrical Engineering, Stanford University",
66		address="Stanford, CA",
67		month=May,
68		year=1976
69		}
70		@INPROCEEDINGS{Mar79,
71		author="Martin, G.N.N.",
72		title="Range encoding: an algorithm for removing redundancy from a digitised
73		message",
74		booktitle="Video & Data Recording Conference",
75		year=1979,
76		address="Southampton",
77		month=Jul
78		}
79		@ARTICLE{MNW98,
80		author="Alistair Moffat and Radford Neal and Ian H. Witten",
81		title="Arithmetic Coding Revisited",
82		journal="{ACM} Transactions on Information Systems",
83		year=1998,
84		volume=16,
85		number=3,
86		pages="256--294",
87		month=Jul,
88		URL="http://www.stanford.edu/class/ee398a/handouts/papers/Moffat98ArithmCoding.pdf"
89		}*/
90
91	29.1M	static int ec_read_byte(ec_dec *_this){
92	29.1M	return _this->offs<_this->storage?_this->buf[_this->offs++]:0;
93	29.1M	}
94
95	2.94M	static int ec_read_byte_from_end(ec_dec *_this){
96	2.94M	return _this->end_offs<_this->storage?
97	2.91M	_this->buf[_this->storage-++(_this->end_offs)]:0;
98	2.94M	}
99
100		/*Normalizes the contents of val and rng so that rng lies entirely in the
101		high-order symbol.*/
102	139M	static void ec_dec_normalize(ec_dec *_this){
103		/If the range is too small, rescale it and input some bits./
104	167M	while(_this->rng<=EC_CODE_BOT){
105	28.4M	int sym;
106	28.4M	_this->nbits_total+=EC_SYM_BITS;
107	28.4M	_this->rng<<=EC_SYM_BITS;
108		/Use up the remaining bits from our last symbol./
109	28.4M	sym=_this->rem;
110		/Read the next value from the input./
111	28.4M	_this->rem=ec_read_byte(_this);
112		/Take the rest of the bits we need from this new symbol./
113	28.4M	sym=(sym<<EC_SYM_BITS\|_this->rem)>>(EC_SYM_BITS-EC_CODE_EXTRA);
114		/And subtract them from val, capped to be less than EC_CODE_TOP./
115	28.4M	_this->val=((_this->val<<EC_SYM_BITS)+(EC_SYM_MAX&~sym))&(EC_CODE_TOP-1);
116	28.4M	}
117	139M	}
118
119	748k	void ec_dec_init(ec_dec _this,unsigned char _buf,opus_uint32 _storage){
120	748k	_this->buf=_buf;
121	748k	_this->storage=_storage;
122	748k	_this->end_offs=0;
123	748k	_this->end_window=0;
124	748k	_this->nend_bits=0;
125		/*This is the offset from which ec_tell() will subtract partial bits.
126		The final value after the ec_dec_normalize() call will be the same as in
127		the encoder, but we have to compensate for the bits that are added there.*/
128	748k	_this->nbits_total=EC_CODE_BITS+1
129	748k	-((EC_CODE_BITS-EC_CODE_EXTRA)/EC_SYM_BITS)*EC_SYM_BITS;
130	748k	_this->offs=0;
131	748k	_this->rng=1U<<EC_CODE_EXTRA;
132	748k	_this->rem=ec_read_byte(_this);
133	748k	_this->val=_this->rng-1-(_this->rem>>(EC_SYM_BITS-EC_CODE_EXTRA));
134	748k	_this->error=0;
135		/Normalize the interval./
136	748k	ec_dec_normalize(_this);
137	748k	}
138
139	2.74M	unsigned ec_decode(ec_dec *_this,unsigned _ft){
140	2.74M	unsigned s;
141	2.74M	_this->ext=celt_udiv(_this->rng,_ft);
142	2.74M	s=(unsigned)(_this->val/_this->ext);
143	2.74M	return _ft-EC_MINI(s+1,_ft);
144	2.74M	}
145
146	2.72M	unsigned ec_decode_bin(ec_dec *_this,unsigned _bits){
147	2.72M	unsigned s;
148	2.72M	_this->ext=_this->rng>>_bits;
149	2.72M	s=(unsigned)(_this->val/_this->ext);
150	2.72M	return (1U<<_bits)-EC_MINI(s+1U,1U<<_bits);
151	2.72M	}
152
153	5.46M	void ec_dec_update(ec_dec *_this,unsigned _fl,unsigned _fh,unsigned _ft){
154	5.46M	opus_uint32 s;
155	5.46M	s=IMUL32(_this->ext,_ft-_fh);
156	5.46M	_this->val-=s;
157	5.46M	_this->rng=_fl>0?IMUL32(_this->ext,_fh-_fl):_this->rng-s;
158	5.46M	ec_dec_normalize(_this);
159	5.46M	}
160
161		/The probability of having a "one" is 1/(1<<_logp)./
162	6.08M	int ec_dec_bit_logp(ec_dec *_this,unsigned _logp){
163	6.08M	opus_uint32 r;
164	6.08M	opus_uint32 d;
165	6.08M	opus_uint32 s;
166	6.08M	int ret;
167	6.08M	r=_this->rng;
168	6.08M	d=_this->val;
169	6.08M	s=r>>_logp;
170	6.08M	ret=d<s;
171	6.08M	if(!ret)_this->val=d-s;
172	6.08M	_this->rng=ret?s:r-s;
173	6.08M	ec_dec_normalize(_this);
174	6.08M	return ret;
175	6.08M	}
176
177	127M	int ec_dec_icdf(ec_dec _this,const unsigned char _icdf,unsigned _ftb){
178	127M	opus_uint32 r;
179	127M	opus_uint32 d;
180	127M	opus_uint32 s;
181	127M	opus_uint32 t;
182	127M	int ret;
183	127M	s=_this->rng;
184	127M	d=_this->val;
185	127M	r=s>>_ftb;
186	127M	ret=-1;
187	318M	do{
188	318M	t=s;
189	318M	s=IMUL32(r,_icdf[++ret]);
190	318M	}
191	318M	while(d<s);
192	127M	_this->val=d-s;
193	127M	_this->rng=t-s;
194	127M	ec_dec_normalize(_this);
195	127M	return ret;
196	127M	}
197
198	0	int ec_dec_icdf16(ec_dec _this,const opus_uint16 _icdf,unsigned _ftb){
199	0	opus_uint32 r;
200	0	opus_uint32 d;
201	0	opus_uint32 s;
202	0	opus_uint32 t;
203	0	int ret;
204	0	s=_this->rng;
205	0	d=_this->val;
206	0	r=s>>_ftb;
207	0	ret=-1;
208	0	do{
209	0	t=s;
210	0	s=IMUL32(r,_icdf[++ret]);
211	0	}
212	0	while(d<s);
213	0	_this->val=d-s;
214	0	_this->rng=t-s;
215	0	ec_dec_normalize(_this);
216	0	return ret;
217	0	}
218
219	2.28M	opus_uint32 ec_dec_uint(ec_dec *_this,opus_uint32 _ft){
220	2.28M	unsigned ft;
221	2.28M	unsigned s;
222	2.28M	int ftb;
223		/In order to optimize EC_ILOG(), it is undefined for the value 0./
224	2.28M	celt_assert(_ft>1);
225	2.28M	_ft--;
226	2.28M	ftb=EC_ILOG(_ft);
227	2.28M	if(ftb>EC_UINT_BITS){
228	1.42M	opus_uint32 t;
229	1.42M	ftb-=EC_UINT_BITS;
230	1.42M	ft=(unsigned)(_ft>>ftb)+1;
231	1.42M	s=ec_decode(_this,ft);
232	1.42M	ec_dec_update(_this,s,s+1,ft);
233	1.42M	t=(opus_uint32)s<<ftb\|ec_dec_bits(_this,ftb);
234	1.42M	if(t<=_ft)return t;
235	7.94k	_this->error=1;
236	7.94k	return _ft;
237	1.42M	}
238	860k	else{
239	860k	_ft++;
240	860k	s=ec_decode(_this,(unsigned)_ft);
241	860k	ec_dec_update(_this,s,s+1,(unsigned)_ft);
242	860k	return s;
243	860k	}
244	2.28M	}
245
246	4.44M	opus_uint32 ec_dec_bits(ec_dec *_this,unsigned _bits){
247	4.44M	ec_window window;
248	4.44M	int available;
249	4.44M	opus_uint32 ret;
250	4.44M	window=_this->end_window;
251	4.44M	available=_this->nend_bits;
252	4.44M	if((unsigned)available<_bits){
253	2.94M	do{
254	2.94M	window\|=(ec_window)ec_read_byte_from_end(_this)<<available;
255	2.94M	available+=EC_SYM_BITS;
256	2.94M	}
257	2.94M	while(available<=EC_WINDOW_SIZE-EC_SYM_BITS);
258	922k	}
259	4.44M	ret=(opus_uint32)window&(((opus_uint32)1<<_bits)-1U);
260	4.44M	window>>=_bits;
261	4.44M	available-=_bits;
262	4.44M	_this->end_window=window;
263	4.44M	_this->nend_bits=available;
264	4.44M	_this->nbits_total+=_bits;
265	4.44M	return ret;
266	4.44M	}