a093f4df74
This unifies the byte buffer, encoder, and decoder into a single
struct.
The common encoder and decoder functions (such as ec_tell()) can
operate on either one, simplifying code which uses both.
The precision argument to ec_tell() has been removed.
It now comes in two precisions:
ec_tell() gives 1 bit precision in two operations, and
ec_tell_frac() gives 1/8th bit precision in... somewhat more.
ec_{enc|dec}_bit_prob() were removed (they are no longer needed).
Some of the byte buffer access functions were made static and
removed from the cross-module API.
All of the code in rangeenc.c and rangedec.c was merged into
entenc.c and entdec.c, respectively, as we are no longer
considering alternative backends.
rangeenc.c and rangede.c have been removed entirely.
This passes make check, after disabling the modes that we removed
support for in cf5d3a8c.
94 lines
3.1 KiB
C
94 lines
3.1 KiB
C
/* Copyright (c) 2001-2011 Timothy B. Terriberry
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*/
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/*
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions
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are met:
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- Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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- Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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- Neither the name of the Xiph.org Foundation nor the names of its
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contributors may be used to endorse or promote products derived from
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this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR
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CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include "entcode.h"
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#if !defined(EC_CLZ)
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int ec_ilog(ec_uint32 _v){
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/*On a Pentium M, this branchless version tested as the fastest on
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1,000,000,000 random 32-bit integers, edging out a similar version with
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branches, and a 256-entry LUT version.*/
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int ret;
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int m;
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ret=!!_v;
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m=!!(_v&0xFFFF0000)<<4;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xFF00)<<3;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xF0)<<2;
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_v>>=m;
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ret|=m;
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m=!!(_v&0xC)<<1;
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_v>>=m;
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ret|=m;
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ret+=!!(_v&0x2);
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return ret;
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}
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#endif
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ec_uint32 ec_tell_frac(ec_ctx *_this){
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ec_uint32 nbits;
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ec_uint32 r;
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int l;
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int i;
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/*To handle the non-integral number of bits still left in the encoder/decoder
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state, we compute the worst-case number of bits of val that must be
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encoded to ensure that the value is inside the range for any possible
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subsequent bits.
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The computation here is independent of val itself (the decoder does not
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even track that value), even though the real number of bits used after
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ec_enc_done() may be 1 smaller if rng is a power of two and the
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corresponding trailing bits of val are all zeros.
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If we did try to track that special case, then coding a value with a
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probability of 1/(1<<n) might sometimes appear to use more than n bits.
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This may help explain the surprising result that a newly initialized
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encoder or decoder claims to have used 1 bit.*/
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nbits=_this->nbits_total<<BITRES;
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l=EC_ILOG(_this->rng);
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r=_this->rng>>l-16;
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for(i=BITRES;i-->0;){
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int b;
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r=r*r>>15;
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b=(int)(r>>16);
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l=l<<1|b;
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r>>=b;
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}
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return nbits-l;
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}
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