/work/vvdec/source/Lib/DecoderLib/BinDecoder.cpp

Source
/* -----------------------------------------------------------------------------
The copyright in this software is being made available under the Clear BSD
License, included below. No patent rights, trademark rights and/or 
other Intellectual Property Rights other than the copyrights concerning 
the Software are granted under this license.

The Clear BSD License

Copyright (c) 2018-2026, Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. & The VVdeC Authors.
All rights reserved.

Redistribution and use in source and binary forms, with or without modification,
are permitted (subject to the limitations in the disclaimer below) 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.

     * Neither the name of the copyright holder nor the names of its
     contributors may be used to endorse or promote products derived from this
     software without specific prior written permission.

NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED BY
THIS LICENSE. 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 HOLDER 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.


------------------------------------------------------------------------------------------- */

/** \file     BinDecoder.cpp
 *  \brief    Low level binary symbol writer
 */


#include "BinDecoder.h"
#include "CommonLib/Rom.h"
#include "CommonLib/BitStream.h"

#include "CommonLib/dtrace_next.h"

#include <limits>

#define CNT_OFFSET 0

namespace vvdec
{

// BinDecoder uses the `signed >> 31` sign-extract idiom, which is implementation-defined
// for negative operands before C++20. Require two's-complement representation so the idiom
// behaves as intended (mandatory anyway in C++20).
static_assert( std::numeric_limits<int>::min() == -std::numeric_limits<int>::max() - 1,
               "two's complement signed integer representation required" );
static_assert( ( -1 >> 1 ) == -1,
               "right shift of negative number needs to be implemented as arithmetic shift." );

void BinDecoder::init( InputBitstream* bitstream )
{
  m_Bitstream = bitstream;
}


void BinDecoder::uninit()
{
  m_Bitstream = 0;
}


void BinDecoder::start()
{
  CHECK( m_Bitstream->getNumBitsUntilByteAligned(), "Bitstream is not byte aligned." );
  m_Range       = 510;
  m_Value       = ( uint32_t( m_Bitstream->readByte() ) << 8 ) + m_Bitstream->readByte();
  m_bitsNeeded  = -8;
}


void BinDecoder::finish()
{
  unsigned lastByte = m_Bitstream->peekPreviousByte();
  CHECK( ( ( lastByte << ( 8 + m_bitsNeeded ) ) & 0xff ) != 0x80,
        "No proper stop/alignment pattern at end of CABAC stream." );
}


void BinDecoder::reset( int qp, int initId )
{
  m_Ctx.init( qp, initId );
  start();
}


unsigned BinDecoder::decodeBinEP()
{
  unsigned value = m_Value << 1;
  if (++m_bitsNeeded >= 0) {
    value += m_Bitstream->readByte();
    m_bitsNeeded = -8;
  }

  unsigned bin = 0;
  unsigned SR = m_Range << 7;
  if (value >= SR) {
    value -= SR;
    bin = 1;
  }
  m_Value = value;
  DTRACE(g_trace_ctx, D_CABAC,
         "%d"
         "  "
         "%d"
         "  EP=%d \n",
         DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), m_Range, bin);
  return bin;
}


unsigned BinDecoder::decodeBinsEP( unsigned numBins )
{
#if ENABLE_TRACING
  int numBinsOrig = numBins;
#endif

  if( m_Range == 256 )
  {
    return decodeAlignedBinsEP( numBins );
  }
  unsigned remBins = numBins;
  unsigned bins    = 0;
  unsigned value   = m_Value;
  unsigned range = m_Range;
  int bitsNeeded = m_bitsNeeded;
  while( remBins > 8 )
  {
    value       = ( value << 8 ) + ( m_Bitstream->readByte() << ( 8 + bitsNeeded ) );
    unsigned SR =   range << 15;
    for( int i = 0; i < 8; i++ )
    {
      bins += bins;
      SR  >>= 1;
      if( value >= SR )
      {
        bins    ++;
        value -= SR;
      }
    }
    remBins -= 8;
  }
  bitsNeeded   += (int)remBins;
  value       <<= remBins;
  if( bitsNeeded >= 0 )
  {
    value      += m_Bitstream->readByte() << bitsNeeded;
    bitsNeeded -= 8;
  }
  unsigned SR = range << ( remBins + 7 );
  for ( unsigned i = 0; i < remBins; i++ )
  {
    bins += bins;
    SR  >>= 1;
    if( value >= SR )
    {
      bins    ++;
      value -= SR;
    }
  }
  m_Value = value;
  m_Range = range;
  m_bitsNeeded = bitsNeeded;
#if ENABLE_TRACING
  for( int i = 0; i < numBinsOrig; i++ )
  {
    DTRACE( g_trace_ctx, D_CABAC, "%d" "  " "%d" "  EP=%d \n", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, ( bins >> ( numBinsOrig - 1 - i ) ) & 1 );
  }
#endif
  return bins;
}

unsigned BinDecoder::decodeRemAbsEP(unsigned goRicePar, unsigned cutoff, int maxLog2TrDynamicRange)
{
  unsigned prefix = 0;
  {
    const unsigned  maxPrefix = 32 - maxLog2TrDynamicRange;
    unsigned        codeWord = 0;
    do
    {
      prefix++;
      codeWord = decodeBinEP();
    } while (codeWord && prefix < maxPrefix);
    prefix -= 1 - (int)codeWord;
  }

  unsigned length = goRicePar, offset;
  if (prefix < cutoff)
  {
    offset = prefix << goRicePar;
  }
  else
  {
    offset = (((1u << (prefix - cutoff)) + cutoff - 1) << goRicePar);
    {
      length += (prefix == (32u - maxLog2TrDynamicRange) ? maxLog2TrDynamicRange - goRicePar : prefix - cutoff);
    }
  }
  return offset + decodeBinsEP(length);
}

unsigned BinDecoder::decodeBinTrm()
{
  m_Range    -= 2;
  unsigned SR = m_Range << 7;
  
  DTRACE( g_trace_ctx, D_CABAC, "%d" " binTrm  range=" "%d" "  bin=%d\n" , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Value >= SR );

  if( m_Value >= SR )
  {
    return 1;
  }
  else
  {
    if( m_Range < 256 )
    {
      m_Range += m_Range;
      m_Value += m_Value;
      if( ++m_bitsNeeded == 0 )
      {
        m_Value      += m_Bitstream->readByte();
        m_bitsNeeded  = -8;
      }
    }
    return 0;
  }
}


void BinDecoder::align()
{
  m_Range = 256;
}

#if ENABLE_TRACING
unsigned int BinDecoder::getNumBitsRead() const
{
  return m_Bitstream->getNumBitsRead() + m_bitsNeeded;
}
#endif   // ENABLE_TRACING

unsigned BinDecoder::decodeAlignedBinsEP( unsigned numBins )
{
#if ENABLE_TRACING
  int numBinsOrig = numBins;
#endif
  unsigned remBins = numBins;
  unsigned bins    = 0;
  while( remBins > 0 )
  {
    // The MSB of m_Value is known to be 0 because range is 256. Therefore:
    //   > The comparison against the symbol range of 128 is simply a test on the next-most-significant bit
    //   > "Subtracting" the symbol range if the decoded bin is 1 simply involves clearing that bit.
    //  As a result, the required bins are simply the <binsToRead> next-most-significant bits of m_Value
    //  (m_Value is stored MSB-aligned in a 16-bit buffer - hence the shift of 15)
    //
    //    m_Value = |0|V|V|V|V|V|V|V|V|B|B|B|B|B|B|B|        (V = usable bit, B = potential buffered bit (buffer refills when m_bitsNeeded >= 0))
    //
    unsigned binsToRead = std::min<unsigned>( remBins, 8 ); //read bytes if able to take advantage of the system's byte-read function
    unsigned binMask    = ( 1 << binsToRead ) - 1;
    unsigned newBins    = ( m_Value >> (15 - binsToRead) ) & binMask;
    bins                = ( bins    << binsToRead) | newBins;
    m_Value             = ( m_Value << binsToRead) & 0x7FFF;
    remBins            -= binsToRead;
    m_bitsNeeded       += (int)binsToRead;
    if( m_bitsNeeded >= 0 )
    {
      m_Value          |= m_Bitstream->readByte() << m_bitsNeeded;
      m_bitsNeeded     -= 8;
    }
  }
#if ENABLE_TRACING
  for( int i = 0; i < numBinsOrig; i++ )
  {
    DTRACE( g_trace_ctx, D_CABAC, "%d" "  " "%d" "  " "EP=%d \n", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, ( bins >> ( numBinsOrig - 1 - i ) ) & 1 );
  }
#endif
  return bins;
}


unsigned BinDecoder::decodeBin( unsigned ctxId )
{
  BinProbModel& rcProbModel = m_Ctx[ctxId];

  unsigned bin, LPS;
  uint32_t range      = m_Range;
  uint32_t value      = m_Value;
  int32_t  bitsNeeded = m_bitsNeeded;

  rcProbModel.lpsmps( range, LPS, bin );

//  DTRACE( g_trace_ctx, D_CABAC, "%d" " xxx " "%d" "  " "[%d:%d]" "  " "%2d(MPS=%d)"  "  " , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Range-LPS, LPS, ( unsigned int )( rcProbModel.state() ), m_Value < ( ( m_Range - LPS ) << 7 ) );
  DTRACE( g_trace_ctx, D_CABAC, "%d" " %d " "%d" "  " "[%d:%d]" "  " "%2d(MPS=%d)"  "  " , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), 666, range, range-LPS, LPS, ( unsigned int )( rcProbModel.state() ), value < ( ( range - LPS ) << 7 ) );
  //DTRACE( g_trace_ctx, D_CABAC, " %d " "%d" "  " "[%d:%d]" "  " "%2d(MPS=%d)"  "  ", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Range - LPS, LPS, (unsigned int)( rcProbModel.state() ), m_Value < ( ( m_Range - LPS ) << 7 ) );

  range      -= LPS;
  uint32_t SR = range << 7;

  int b = ~( ( int( value ) - int( SR ) ) >> 31 );
  int a = ~b & ( ( int( range ) - 256 ) >> 31 );
  //int b = -( Value >= SR );
  
  int numBits  = ( a & rcProbModel.getRenormBitsRange( range ) ) | ( b & rcProbModel.getRenormBitsLPS( LPS ) );
  
  value       -= b & SR;
  value      <<= numBits;
  
  range       &=  ~b;
  range       |= ( b & LPS );
  range      <<= numBits;
  
  // b    0 0 1 1
  // bin  0 1 0 1
  // res  0 1 1 0

  //bin          = ( ~b & bin ) | ( b & !bin );
  bin         ^= b;
  bin         &= 1;
  
  bitsNeeded  += numBits & ( a | b );
  
  const int c = ~(bitsNeeded >> 31);
  value      += uint32_t( m_Bitstream->readByteFlag( c ) ) << ( bitsNeeded & 31 );
  bitsNeeded -= c & 8;
  
  //if( Value < SR )
  //{
  //  // MPS path
  //  if( Range < 256 )
  //  {
  //    int numBits   = rcProbModel.getRenormBitsRange( Range );
  //    Range       <<= numBits;
  //    Value       <<= numBits;
  //    bitsNeeded   += numBits;
  //    if( bitsNeeded >= 0 )
  //    {
  //      Value      += m_Bitstream->readByte() << bitsNeeded;
  //      bitsNeeded -= 8;
  //    }
  //  }
  //}
  //else
  //{
  //  bin = !bin;
  //  // LPS path
  //  int numBits   = rcProbModel.getRenormBitsLPS( LPS );
  //  Value        -= SR;
  //  Value       <<= numBits;
  //  Range         = LPS     << numBits;
  //  bitsNeeded   += numBits;
  //  if( bitsNeeded >= 0 )
  //  {
  //    Value      += m_Bitstream->readByte() << bitsNeeded;
  //    bitsNeeded -= 8;
  //  }
  //}

  m_Range      = range;
  m_Value      = value;
  m_bitsNeeded = bitsNeeded;

  rcProbModel.update( bin );
  DTRACE_WITHOUT_COUNT( g_trace_ctx, D_CABAC, "  -  " "%d" "\n", bin );
  return  bin;
}

}

Coverage Report

Created: 2026-06-15 06:25

Line	Count	Source
1		/* -----------------------------------------------------------------------------
2		The copyright in this software is being made available under the Clear BSD
3		License, included below. No patent rights, trademark rights and/or
4		other Intellectual Property Rights other than the copyrights concerning
5		the Software are granted under this license.
6
7		The Clear BSD License
8
9		Copyright (c) 2018-2026, Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. & The VVdeC Authors.
10		All rights reserved.
11
12		Redistribution and use in source and binary forms, with or without modification,
13		are permitted (subject to the limitations in the disclaimer below) provided that
14		the following conditions are met:
15
16		* Redistributions of source code must retain the above copyright notice,
17		this list of conditions and the following disclaimer.
18
19		* Redistributions in binary form must reproduce the above copyright
20		notice, this list of conditions and the following disclaimer in the
21		documentation and/or other materials provided with the distribution.
22
23		* Neither the name of the copyright holder nor the names of its
24		contributors may be used to endorse or promote products derived from this
25		software without specific prior written permission.
26
27		NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED BY
28		THIS LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
29		CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30		LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
31		PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
32		CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
33		EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
34		PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
35		BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
36		IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
37		ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
38		POSSIBILITY OF SUCH DAMAGE.
39
40
41		------------------------------------------------------------------------------------------- */
42
43		/** \file BinDecoder.cpp
44		* \brief Low level binary symbol writer
45		*/
46
47
48		#include "BinDecoder.h"
49		#include "CommonLib/Rom.h"
50		#include "CommonLib/BitStream.h"
51
52		#include "CommonLib/dtrace_next.h"
53
54		#include <limits>
55
56		#define CNT_OFFSET 0
57
58		namespace vvdec
59		{
60
61		// BinDecoder uses the `signed >> 31` sign-extract idiom, which is implementation-defined
62		// for negative operands before C++20. Require two's-complement representation so the idiom
63		// behaves as intended (mandatory anyway in C++20).
64		static_assert( std::numeric_limits<int>::min() == -std::numeric_limits<int>::max() - 1,
65		"two's complement signed integer representation required" );
66		static_assert( ( -1 >> 1 ) == -1,
67		"right shift of negative number needs to be implemented as arithmetic shift." );
68
69		void BinDecoder::init( InputBitstream* bitstream )
70	0	{
71	0	m_Bitstream = bitstream;
72	0	}
73
74
75		void BinDecoder::uninit()
76	0	{
77	0	m_Bitstream = 0;
78	0	}
79
80
81		void BinDecoder::start()
82	0	{
83	0	CHECK( m_Bitstream->getNumBitsUntilByteAligned(), "Bitstream is not byte aligned." );
84	0	m_Range = 510;
85	0	m_Value = ( uint32_t( m_Bitstream->readByte() ) << 8 ) + m_Bitstream->readByte();
86	0	m_bitsNeeded = -8;
87	0	}
88
89
90		void BinDecoder::finish()
91	0	{
92	0	unsigned lastByte = m_Bitstream->peekPreviousByte();
93	0	CHECK( ( ( lastByte << ( 8 + m_bitsNeeded ) ) & 0xff ) != 0x80,
94	0	"No proper stop/alignment pattern at end of CABAC stream." );
95	0	}
96
97
98		void BinDecoder::reset( int qp, int initId )
99	0	{
100	0	m_Ctx.init( qp, initId );
101	0	start();
102	0	}
103
104
105		unsigned BinDecoder::decodeBinEP()
106	0	{
107	0	unsigned value = m_Value << 1;
108	0	if (++m_bitsNeeded >= 0) {
109	0	value += m_Bitstream->readByte();
110	0	m_bitsNeeded = -8;
111	0	}
112
113	0	unsigned bin = 0;
114	0	unsigned SR = m_Range << 7;
115	0	if (value >= SR) {
116	0	value -= SR;
117	0	bin = 1;
118	0	}
119	0	m_Value = value;
120	0	DTRACE(g_trace_ctx, D_CABAC,
121	0	"%d"
122	0	" "
123	0	"%d"
124	0	" EP=%d \n",
125	0	DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), m_Range, bin);
126	0	return bin;
127	0	}
128
129
130		unsigned BinDecoder::decodeBinsEP( unsigned numBins )
131	0	{
132		#if ENABLE_TRACING
133		int numBinsOrig = numBins;
134		#endif
135
136	0	if( m_Range == 256 )
137	0	{
138	0	return decodeAlignedBinsEP( numBins );
139	0	}
140	0	unsigned remBins = numBins;
141	0	unsigned bins = 0;
142	0	unsigned value = m_Value;
143	0	unsigned range = m_Range;
144	0	int bitsNeeded = m_bitsNeeded;
145	0	while( remBins > 8 )
146	0	{
147	0	value = ( value << 8 ) + ( m_Bitstream->readByte() << ( 8 + bitsNeeded ) );
148	0	unsigned SR = range << 15;
149	0	for( int i = 0; i < 8; i++ )
150	0	{
151	0	bins += bins;
152	0	SR >>= 1;
153	0	if( value >= SR )
154	0	{
155	0	bins ++;
156	0	value -= SR;
157	0	}
158	0	}
159	0	remBins -= 8;
160	0	}
161	0	bitsNeeded += (int)remBins;
162	0	value <<= remBins;
163	0	if( bitsNeeded >= 0 )
164	0	{
165	0	value += m_Bitstream->readByte() << bitsNeeded;
166	0	bitsNeeded -= 8;
167	0	}
168	0	unsigned SR = range << ( remBins + 7 );
169	0	for ( unsigned i = 0; i < remBins; i++ )
170	0	{
171	0	bins += bins;
172	0	SR >>= 1;
173	0	if( value >= SR )
174	0	{
175	0	bins ++;
176	0	value -= SR;
177	0	}
178	0	}
179	0	m_Value = value;
180	0	m_Range = range;
181	0	m_bitsNeeded = bitsNeeded;
182		#if ENABLE_TRACING
183		for( int i = 0; i < numBinsOrig; i++ )
184		{
185		DTRACE( g_trace_ctx, D_CABAC, "%d" " " "%d" " EP=%d \n", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, ( bins >> ( numBinsOrig - 1 - i ) ) & 1 );
186		}
187		#endif
188	0	return bins;
189	0	}
190
191		unsigned BinDecoder::decodeRemAbsEP(unsigned goRicePar, unsigned cutoff, int maxLog2TrDynamicRange)
192	0	{
193	0	unsigned prefix = 0;
194	0	{
195	0	const unsigned maxPrefix = 32 - maxLog2TrDynamicRange;
196	0	unsigned codeWord = 0;
197	0	do
198	0	{
199	0	prefix++;
200	0	codeWord = decodeBinEP();
201	0	} while (codeWord && prefix < maxPrefix);
202	0	prefix -= 1 - (int)codeWord;
203	0	}
204
205	0	unsigned length = goRicePar, offset;
206	0	if (prefix < cutoff)
207	0	{
208	0	offset = prefix << goRicePar;
209	0	}
210	0	else
211	0	{
212	0	offset = (((1u << (prefix - cutoff)) + cutoff - 1) << goRicePar);
213	0	{
214	0	length += (prefix == (32u - maxLog2TrDynamicRange) ? maxLog2TrDynamicRange - goRicePar : prefix - cutoff);
215	0	}
216	0	}
217	0	return offset + decodeBinsEP(length);
218	0	}
219
220		unsigned BinDecoder::decodeBinTrm()
221	0	{
222	0	m_Range -= 2;
223	0	unsigned SR = m_Range << 7;
224
225	0	DTRACE( g_trace_ctx, D_CABAC, "%d" " binTrm range=" "%d" " bin=%d\n" , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Value >= SR );
226
227	0	if( m_Value >= SR )
228	0	{
229	0	return 1;
230	0	}
231	0	else
232	0	{
233	0	if( m_Range < 256 )
234	0	{
235	0	m_Range += m_Range;
236	0	m_Value += m_Value;
237	0	if( ++m_bitsNeeded == 0 )
238	0	{
239	0	m_Value += m_Bitstream->readByte();
240	0	m_bitsNeeded = -8;
241	0	}
242	0	}
243	0	return 0;
244	0	}
245	0	}
246
247
248		void BinDecoder::align()
249	0	{
250	0	m_Range = 256;
251	0	}
252
253		#if ENABLE_TRACING
254		unsigned int BinDecoder::getNumBitsRead() const
255		{
256		return m_Bitstream->getNumBitsRead() + m_bitsNeeded;
257		}
258		#endif // ENABLE_TRACING
259
260		unsigned BinDecoder::decodeAlignedBinsEP( unsigned numBins )
261	0	{
262		#if ENABLE_TRACING
263		int numBinsOrig = numBins;
264		#endif
265	0	unsigned remBins = numBins;
266	0	unsigned bins = 0;
267	0	while( remBins > 0 )
268	0	{
269		// The MSB of m_Value is known to be 0 because range is 256. Therefore:
270		// > The comparison against the symbol range of 128 is simply a test on the next-most-significant bit
271		// > "Subtracting" the symbol range if the decoded bin is 1 simply involves clearing that bit.
272		// As a result, the required bins are simply the <binsToRead> next-most-significant bits of m_Value
273		// (m_Value is stored MSB-aligned in a 16-bit buffer - hence the shift of 15)
274		//
275		// m_Value = \|0\|V\|V\|V\|V\|V\|V\|V\|V\|B\|B\|B\|B\|B\|B\|B\| (V = usable bit, B = potential buffered bit (buffer refills when m_bitsNeeded >= 0))
276		//
277	0	unsigned binsToRead = std::min<unsigned>( remBins, 8 ); //read bytes if able to take advantage of the system's byte-read function
278	0	unsigned binMask = ( 1 << binsToRead ) - 1;
279	0	unsigned newBins = ( m_Value >> (15 - binsToRead) ) & binMask;
280	0	bins = ( bins << binsToRead) \| newBins;
281	0	m_Value = ( m_Value << binsToRead) & 0x7FFF;
282	0	remBins -= binsToRead;
283	0	m_bitsNeeded += (int)binsToRead;
284	0	if( m_bitsNeeded >= 0 )
285	0	{
286	0	m_Value \|= m_Bitstream->readByte() << m_bitsNeeded;
287	0	m_bitsNeeded -= 8;
288	0	}
289	0	}
290		#if ENABLE_TRACING
291		for( int i = 0; i < numBinsOrig; i++ )
292		{
293		DTRACE( g_trace_ctx, D_CABAC, "%d" " " "%d" " " "EP=%d \n", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, ( bins >> ( numBinsOrig - 1 - i ) ) & 1 );
294		}
295		#endif
296	0	return bins;
297	0	}
298
299
300		unsigned BinDecoder::decodeBin( unsigned ctxId )
301	0	{
302	0	BinProbModel& rcProbModel = m_Ctx[ctxId];
303
304	0	unsigned bin, LPS;
305	0	uint32_t range = m_Range;
306	0	uint32_t value = m_Value;
307	0	int32_t bitsNeeded = m_bitsNeeded;
308
309	0	rcProbModel.lpsmps( range, LPS, bin );
310
311		// DTRACE( g_trace_ctx, D_CABAC, "%d" " xxx " "%d" " " "[%d:%d]" " " "%2d(MPS=%d)" " " , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Range-LPS, LPS, ( unsigned int )( rcProbModel.state() ), m_Value < ( ( m_Range - LPS ) << 7 ) );
312	0	DTRACE( g_trace_ctx, D_CABAC, "%d" " %d " "%d" " " "[%d:%d]" " " "%2d(MPS=%d)" " " , DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), 666, range, range-LPS, LPS, ( unsigned int )( rcProbModel.state() ), value < ( ( range - LPS ) << 7 ) );
313		//DTRACE( g_trace_ctx, D_CABAC, " %d " "%d" " " "[%d:%d]" " " "%2d(MPS=%d)" " ", DTRACE_GET_COUNTER( g_trace_ctx, D_CABAC ), m_Range, m_Range - LPS, LPS, (unsigned int)( rcProbModel.state() ), m_Value < ( ( m_Range - LPS ) << 7 ) );
314
315	0	range -= LPS;
316	0	uint32_t SR = range << 7;
317
318	0	int b = ~( ( int( value ) - int( SR ) ) >> 31 );
319	0	int a = ~b & ( ( int( range ) - 256 ) >> 31 );
320		//int b = -( Value >= SR );
321
322	0	int numBits = ( a & rcProbModel.getRenormBitsRange( range ) ) \| ( b & rcProbModel.getRenormBitsLPS( LPS ) );
323
324	0	value -= b & SR;
325	0	value <<= numBits;
326
327	0	range &= ~b;
328	0	range \|= ( b & LPS );
329	0	range <<= numBits;
330
331		// b 0 0 1 1
332		// bin 0 1 0 1
333		// res 0 1 1 0
334
335		//bin = ( ~b & bin ) \| ( b & !bin );
336	0	bin ^= b;
337	0	bin &= 1;
338
339	0	bitsNeeded += numBits & ( a \| b );
340
341	0	const int c = ~(bitsNeeded >> 31);
342	0	value += uint32_t( m_Bitstream->readByteFlag( c ) ) << ( bitsNeeded & 31 );
343	0	bitsNeeded -= c & 8;
344
345		//if( Value < SR )
346		//{
347		// // MPS path
348		// if( Range < 256 )
349		// {
350		// int numBits = rcProbModel.getRenormBitsRange( Range );
351		// Range <<= numBits;
352		// Value <<= numBits;
353		// bitsNeeded += numBits;
354		// if( bitsNeeded >= 0 )
355		// {
356		// Value += m_Bitstream->readByte() << bitsNeeded;
357		// bitsNeeded -= 8;
358		// }
359		// }
360		//}
361		//else
362		//{
363		// bin = !bin;
364		// // LPS path
365		// int numBits = rcProbModel.getRenormBitsLPS( LPS );
366		// Value -= SR;
367		// Value <<= numBits;
368		// Range = LPS << numBits;
369		// bitsNeeded += numBits;
370		// if( bitsNeeded >= 0 )
371		// {
372		// Value += m_Bitstream->readByte() << bitsNeeded;
373		// bitsNeeded -= 8;
374		// }
375		//}
376
377	0	m_Range = range;
378	0	m_Value = value;
379	0	m_bitsNeeded = bitsNeeded;
380
381	0	rcProbModel.update( bin );
382	0	DTRACE_WITHOUT_COUNT( g_trace_ctx, D_CABAC, " - " "%d" "\n", bin );
383	0	return bin;
384	0	}
385
386		}