299 lines
9.3 KiB
C
299 lines
9.3 KiB
C
/* Copyright (c) 2001-2011 Timothy B. Terriberry
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Copyright (c) 2008-2009 Xiph.Org Foundation */
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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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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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#if defined(HAVE_CONFIG_H)
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# include "config.h"
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#endif
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#include "os_support.h"
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#include "arch.h"
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#include "entenc.h"
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#include "mfrngcod.h"
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/*A range encoder.
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See entdec.c and the references for implementation details \cite{Mar79,MNW98}.
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@INPROCEEDINGS{Mar79,
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author="Martin, G.N.N.",
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title="Range encoding: an algorithm for removing redundancy from a digitised
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message",
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booktitle="Video \& Data Recording Conference",
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year=1979,
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address="Southampton",
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month=Jul
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}
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@ARTICLE{MNW98,
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author="Alistair Moffat and Radford Neal and Ian H. Witten",
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title="Arithmetic Coding Revisited",
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journal="{ACM} Transactions on Information Systems",
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year=1998,
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volume=16,
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number=3,
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pages="256--294",
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month=Jul,
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URL="http://www.stanford.edu/class/ee398/handouts/papers/Moffat98ArithmCoding.pdf"
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}*/
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static int ec_write_byte(ec_enc *_this,unsigned _value){
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if(_this->offs+_this->end_offs>=_this->storage)return -1;
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_this->buf[_this->offs++]=(unsigned char)_value;
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return 0;
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}
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static int ec_write_byte_at_end(ec_enc *_this,unsigned _value){
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if(_this->offs+_this->end_offs>=_this->storage)return -1;
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_this->buf[_this->storage-++(_this->end_offs)]=(unsigned char)_value;
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return 0;
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}
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/*Outputs a symbol, with a carry bit.
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If there is a potential to propagate a carry over several symbols, they are
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buffered until it can be determined whether or not an actual carry will
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occur.
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If the counter for the buffered symbols overflows, then the stream becomes
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undecodable.
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This gives a theoretical limit of a few billion symbols in a single packet on
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32-bit systems.
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The alternative is to truncate the range in order to force a carry, but
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requires similar carry tracking in the decoder, needlessly slowing it down.*/
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static void ec_enc_carry_out(ec_enc *_this,int _c){
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if(_c!=EC_SYM_MAX){
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/*No further carry propagation possible, flush buffer.*/
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int carry;
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carry=_c>>EC_SYM_BITS;
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/*Don't output a byte on the first write.
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This compare should be taken care of by branch-prediction thereafter.*/
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if(_this->rem>=0)_this->error|=ec_write_byte(_this,_this->rem+carry);
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if(_this->ext>0){
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unsigned sym;
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sym=EC_SYM_MAX+carry&EC_SYM_MAX;
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do _this->error|=ec_write_byte(_this,sym);
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while(--(_this->ext)>0);
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}
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_this->rem=_c&EC_SYM_MAX;
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}
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else _this->ext++;
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}
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static void ec_enc_normalize(ec_enc *_this){
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/*If the range is too small, output some bits and rescale it.*/
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while(_this->rng<=EC_CODE_BOT){
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ec_enc_carry_out(_this,(int)(_this->val>>EC_CODE_SHIFT));
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/*Move the next-to-high-order symbol into the high-order position.*/
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_this->val=_this->val<<EC_SYM_BITS&EC_CODE_TOP-1;
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_this->rng<<=EC_SYM_BITS;
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_this->nbits_total+=EC_SYM_BITS;
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}
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}
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void ec_enc_init(ec_enc *_this,unsigned char *_buf,celt_uint32 _size){
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_this->buf=_buf;
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_this->end_offs=0;
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_this->end_window=0;
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_this->nend_bits=0;
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/*This is the offset from which ec_tell() will subtract partial bits.*/
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_this->nbits_total=EC_CODE_BITS+1;
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_this->offs=0;
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_this->rng=EC_CODE_TOP;
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_this->rem=-1;
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_this->val=0;
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_this->ext=0;
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_this->storage=_size;
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_this->error=0;
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}
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void ec_encode(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _ft){
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celt_uint32 r;
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r=_this->rng/_ft;
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if(_fl>0){
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_this->val+=_this->rng-IMUL32(r,(_ft-_fl));
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_this->rng=IMUL32(r,(_fh-_fl));
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}
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else _this->rng-=IMUL32(r,(_ft-_fh));
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ec_enc_normalize(_this);
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}
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void ec_encode_bin(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _bits){
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celt_uint32 r;
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r=_this->rng>>_bits;
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if(_fl>0){
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_this->val+=_this->rng-IMUL32(r,((1<<_bits)-_fl));
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_this->rng=IMUL32(r,(_fh-_fl));
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}
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else _this->rng-=IMUL32(r,((1<<_bits)-_fh));
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ec_enc_normalize(_this);
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}
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/*The probability of having a "one" is 1/(1<<_logp).*/
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void ec_enc_bit_logp(ec_enc *_this,int _val,unsigned _logp){
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celt_uint32 r;
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celt_uint32 s;
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celt_uint32 l;
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r=_this->rng;
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l=_this->val;
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s=r>>_logp;
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r-=s;
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if(_val)_this->val=l+r;
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_this->rng=_val?s:r;
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ec_enc_normalize(_this);
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}
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void ec_enc_icdf(ec_enc *_this,int _s,const unsigned char *_icdf,unsigned _ftb){
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celt_uint32 r;
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r=_this->rng>>_ftb;
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if(_s>0){
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_this->val+=_this->rng-IMUL32(r,_icdf[_s-1]);
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_this->rng=IMUL32(r,_icdf[_s-1]-_icdf[_s]);
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}
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else _this->rng-=IMUL32(r,_icdf[_s]);
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ec_enc_normalize(_this);
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}
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void ec_enc_uint(ec_enc *_this,celt_uint32 _fl,celt_uint32 _ft){
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unsigned ft;
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unsigned fl;
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int ftb;
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/*In order to optimize EC_ILOG(), it is undefined for the value 0.*/
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celt_assert(_ft>1);
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_ft--;
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ftb=EC_ILOG(_ft);
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if(ftb>EC_UINT_BITS){
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ftb-=EC_UINT_BITS;
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ft=(_ft>>ftb)+1;
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fl=(unsigned)(_fl>>ftb);
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ec_encode(_this,fl,fl+1,ft);
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ec_enc_bits(_this,_fl&((celt_uint32)1<<ftb)-1,ftb);
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}
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else ec_encode(_this,_fl,_fl+1,_ft+1);
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}
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void ec_enc_bits(ec_enc *_this,celt_uint32 _fl,unsigned _bits){
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ec_window window;
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int used;
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window=_this->end_window;
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used=_this->nend_bits;
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if(used+_bits>EC_WINDOW_SIZE){
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do{
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_this->error|=ec_write_byte_at_end(_this,(unsigned)window&EC_SYM_MAX);
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window>>=EC_SYM_BITS;
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used-=EC_SYM_BITS;
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}
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while(used>=EC_SYM_BITS);
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}
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window|=(ec_window)_fl<<used;
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used+=_bits;
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_this->end_window=window;
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_this->nend_bits=used;
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_this->nbits_total+=_bits;
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}
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void ec_enc_patch_initial_bits(ec_enc *_this,unsigned _val,unsigned _nbits){
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int shift;
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unsigned mask;
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celt_assert(_nbits<=EC_SYM_BITS);
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shift=EC_SYM_BITS-_nbits;
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mask=(1<<_nbits)-1<<shift;
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if(_this->offs>0){
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/*The first byte has been finalized.*/
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_this->buf[0]=(unsigned char)(_this->buf[0]&~mask|_val<<shift);
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}
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else if(_this->rem>=0){
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/*The first byte is still awaiting carry propagation.*/
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_this->rem=_this->rem&~mask|_val<<shift;
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}
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else if(_this->rng<=EC_CODE_TOP>>shift){
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/*The renormalization loop has never been run.*/
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_this->val=_this->val&~((celt_uint32)mask<<EC_CODE_SHIFT)|
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(celt_uint32)_val<<EC_CODE_SHIFT+shift;
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}
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/*The encoder hasn't even encoded _nbits of data yet.*/
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else _this->error=-1;
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}
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void ec_enc_shrink(ec_enc *_this,celt_uint32 _size){
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celt_assert(_this->offs+_this->end_offs<=_size);
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CELT_MOVE(_this->buf+_size-_this->end_offs,
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_this->buf+_this->storage-_this->end_offs,_this->end_offs);
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_this->storage=_size;
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}
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void ec_enc_done(ec_enc *_this){
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ec_window window;
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int used;
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celt_uint32 msk;
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celt_uint32 end;
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int l;
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/*We output the minimum number of bits that ensures that the symbols encoded
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thus far will be decoded correctly regardless of the bits that follow.*/
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l=EC_CODE_BITS-EC_ILOG(_this->rng);
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msk=EC_CODE_TOP-1>>l;
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end=_this->val+msk&~msk;
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if((end|msk)>=_this->val+_this->rng){
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l++;
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msk>>=1;
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end=_this->val+msk&~msk;
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}
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while(l>0){
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ec_enc_carry_out(_this,(int)(end>>EC_CODE_SHIFT));
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end=end<<EC_SYM_BITS&EC_CODE_TOP-1;
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l-=EC_SYM_BITS;
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}
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/*If we have a buffered byte flush it into the output buffer.*/
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if(_this->rem>=0||_this->ext>0)ec_enc_carry_out(_this,0);
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/*If we have buffered extra bits, flush them as well.*/
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window=_this->end_window;
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used=_this->nend_bits;
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while(used>=EC_SYM_BITS){
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_this->error|=ec_write_byte_at_end(_this,(unsigned)window&EC_SYM_MAX);
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window>>=EC_SYM_BITS;
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used-=EC_SYM_BITS;
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}
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/*Clear any excess space and add any remaining extra bits to the last byte.*/
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if(!_this->error){
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CELT_MEMSET(_this->buf+_this->offs,0,
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_this->storage-_this->offs-_this->end_offs);
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if(used>0){
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/*If there's no range coder data at all, give up.*/
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if(_this->end_offs>=_this->storage)_this->error=-1;
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else{
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l=-l;
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/*If we've busted, don't add too many extra bits to the last byte; it
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would corrupt the range coder data, and that's more important.*/
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if(_this->offs+_this->end_offs>=_this->storage&&l<used){
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window&=(1<<l)-1;
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_this->error=-1;
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}
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}
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_this->buf[_this->storage-_this->end_offs-1]|=(unsigned char)window;
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}
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}
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}
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