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+/* 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.
+*/
+
+#if defined(HAVE_CONFIG_H)
+# include "config.h"
+#endif
+#include "os_support.h"
+#include "arch.h"
+#include "entenc.h"
+#include "mfrngcod.h"
+
+/*A range encoder.
+ See entdec.c and the references for implementation details \cite{Mar79,MNW98}.
+
+ @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/ee398/handouts/papers/Moffat98ArithmCoding.pdf"
+ }*/
+
+static int ec_write_byte(ec_enc *_this,unsigned _value){
+ if(_this->offs+_this->end_offs>=_this->storage)return -1;
+ _this->buf[_this->offs++]=(unsigned char)_value;
+ return 0;
+}
+
+static int ec_write_byte_at_end(ec_enc *_this,unsigned _value){
+ if(_this->offs+_this->end_offs>=_this->storage)return -1;
+ _this->buf[_this->storage-++(_this->end_offs)]=(unsigned char)_value;
+ return 0;
+}
+
+/*Outputs a symbol, with a carry bit.
+ If there is a potential to propagate a carry over several symbols, they are
+ buffered until it can be determined whether or not an actual carry will
+ occur.
+ If the counter for the buffered symbols overflows, then the stream becomes
+ undecodable.
+ This gives a theoretical limit of a few billion symbols in a single packet on
+ 32-bit systems.
+ The alternative is to truncate the range in order to force a carry, but
+ requires similar carry tracking in the decoder, needlessly slowing it down.*/
+static void ec_enc_carry_out(ec_enc *_this,int _c){
+ if(_c!=EC_SYM_MAX){
+ /*No further carry propagation possible, flush buffer.*/
+ int carry;
+ carry=_c>>EC_SYM_BITS;
+ /*Don't output a byte on the first write.
+ This compare should be taken care of by branch-prediction thereafter.*/
+ if(_this->rem>=0)_this->error|=ec_write_byte(_this,_this->rem+carry);
+ if(_this->ext>0){
+ unsigned sym;
+ sym=(EC_SYM_MAX+carry)&EC_SYM_MAX;
+ do _this->error|=ec_write_byte(_this,sym);
+ while(--(_this->ext)>0);
+ }
+ _this->rem=_c&EC_SYM_MAX;
+ }
+ else _this->ext++;
+}
+
+static OPUS_INLINE void ec_enc_normalize(ec_enc *_this){
+ /*If the range is too small, output some bits and rescale it.*/
+ while(_this->rng<=EC_CODE_BOT){
+ ec_enc_carry_out(_this,(int)(_this->val>>EC_CODE_SHIFT));
+ /*Move the next-to-high-order symbol into the high-order position.*/
+ _this->val=(_this->val<<EC_SYM_BITS)&(EC_CODE_TOP-1);
+ _this->rng<<=EC_SYM_BITS;
+ _this->nbits_total+=EC_SYM_BITS;
+ }
+}
+
+void ec_enc_init(ec_enc *_this,unsigned char *_buf,opus_uint32 _size){
+ _this->buf=_buf;
+ _this->end_offs=0;
+ _this->end_window=0;
+ _this->nend_bits=0;
+ /*This is the offset from which ec_tell() will subtract partial bits.*/
+ _this->nbits_total=EC_CODE_BITS+1;
+ _this->offs=0;
+ _this->rng=EC_CODE_TOP;
+ _this->rem=-1;
+ _this->val=0;
+ _this->ext=0;
+ _this->storage=_size;
+ _this->error=0;
+}
+
+void ec_encode(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _ft){
+ opus_uint32 r;
+ r=celt_udiv(_this->rng,_ft);
+ if(_fl>0){
+ _this->val+=_this->rng-IMUL32(r,(_ft-_fl));
+ _this->rng=IMUL32(r,(_fh-_fl));
+ }
+ else _this->rng-=IMUL32(r,(_ft-_fh));
+ ec_enc_normalize(_this);
+}
+
+void ec_encode_bin(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _bits){
+ opus_uint32 r;
+ r=_this->rng>>_bits;
+ if(_fl>0){
+ _this->val+=_this->rng-IMUL32(r,((1U<<_bits)-_fl));
+ _this->rng=IMUL32(r,(_fh-_fl));
+ }
+ else _this->rng-=IMUL32(r,((1U<<_bits)-_fh));
+ ec_enc_normalize(_this);
+}
+
+/*The probability of having a "one" is 1/(1<<_logp).*/
+void ec_enc_bit_logp(ec_enc *_this,int _val,unsigned _logp){
+ opus_uint32 r;
+ opus_uint32 s;
+ opus_uint32 l;
+ r=_this->rng;
+ l=_this->val;
+ s=r>>_logp;
+ r-=s;
+ if(_val)_this->val=l+r;
+ _this->rng=_val?s:r;
+ ec_enc_normalize(_this);
+}
+
+void ec_enc_icdf(ec_enc *_this,int _s,const unsigned char *_icdf,unsigned _ftb){
+ opus_uint32 r;
+ r=_this->rng>>_ftb;
+ if(_s>0){
+ _this->val+=_this->rng-IMUL32(r,_icdf[_s-1]);
+ _this->rng=IMUL32(r,_icdf[_s-1]-_icdf[_s]);
+ }
+ else _this->rng-=IMUL32(r,_icdf[_s]);
+ ec_enc_normalize(_this);
+}
+
+void ec_enc_uint(ec_enc *_this,opus_uint32 _fl,opus_uint32 _ft){
+ unsigned ft;
+ unsigned fl;
+ 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){
+ ftb-=EC_UINT_BITS;
+ ft=(_ft>>ftb)+1;
+ fl=(unsigned)(_fl>>ftb);
+ ec_encode(_this,fl,fl+1,ft);
+ ec_enc_bits(_this,_fl&(((opus_uint32)1<<ftb)-1U),ftb);
+ }
+ else ec_encode(_this,_fl,_fl+1,_ft+1);
+}
+
+void ec_enc_bits(ec_enc *_this,opus_uint32 _fl,unsigned _bits){
+ ec_window window;
+ int used;
+ window=_this->end_window;
+ used=_this->nend_bits;
+ celt_assert(_bits>0);
+ if(used+_bits>EC_WINDOW_SIZE){
+ do{
+ _this->error|=ec_write_byte_at_end(_this,(unsigned)window&EC_SYM_MAX);
+ window>>=EC_SYM_BITS;
+ used-=EC_SYM_BITS;
+ }
+ while(used>=EC_SYM_BITS);
+ }
+ window|=(ec_window)_fl<<used;
+ used+=_bits;
+ _this->end_window=window;
+ _this->nend_bits=used;
+ _this->nbits_total+=_bits;
+}
+
+void ec_enc_patch_initial_bits(ec_enc *_this,unsigned _val,unsigned _nbits){
+ int shift;
+ unsigned mask;
+ celt_assert(_nbits<=EC_SYM_BITS);
+ shift=EC_SYM_BITS-_nbits;
+ mask=((1<<_nbits)-1)<<shift;
+ if(_this->offs>0){
+ /*The first byte has been finalized.*/
+ _this->buf[0]=(unsigned char)((_this->buf[0]&~mask)|_val<<shift);
+ }
+ else if(_this->rem>=0){
+ /*The first byte is still awaiting carry propagation.*/
+ _this->rem=(_this->rem&~mask)|_val<<shift;
+ }
+ else if(_this->rng<=(EC_CODE_TOP>>_nbits)){
+ /*The renormalization loop has never been run.*/
+ _this->val=(_this->val&~((opus_uint32)mask<<EC_CODE_SHIFT))|
+ (opus_uint32)_val<<(EC_CODE_SHIFT+shift);
+ }
+ /*The encoder hasn't even encoded _nbits of data yet.*/
+ else _this->error=-1;
+}
+
+void ec_enc_shrink(ec_enc *_this,opus_uint32 _size){
+ celt_assert(_this->offs+_this->end_offs<=_size);
+ OPUS_MOVE(_this->buf+_size-_this->end_offs,
+ _this->buf+_this->storage-_this->end_offs,_this->end_offs);
+ _this->storage=_size;
+}
+
+void ec_enc_done(ec_enc *_this){
+ ec_window window;
+ int used;
+ opus_uint32 msk;
+ opus_uint32 end;
+ int l;
+ /*We output the minimum number of bits that ensures that the symbols encoded
+ thus far will be decoded correctly regardless of the bits that follow.*/
+ l=EC_CODE_BITS-EC_ILOG(_this->rng);
+ msk=(EC_CODE_TOP-1)>>l;
+ end=(_this->val+msk)&~msk;
+ if((end|msk)>=_this->val+_this->rng){
+ l++;
+ msk>>=1;
+ end=(_this->val+msk)&~msk;
+ }
+ while(l>0){
+ ec_enc_carry_out(_this,(int)(end>>EC_CODE_SHIFT));
+ end=(end<<EC_SYM_BITS)&(EC_CODE_TOP-1);
+ l-=EC_SYM_BITS;
+ }
+ /*If we have a buffered byte flush it into the output buffer.*/
+ if(_this->rem>=0||_this->ext>0)ec_enc_carry_out(_this,0);
+ /*If we have buffered extra bits, flush them as well.*/
+ window=_this->end_window;
+ used=_this->nend_bits;
+ while(used>=EC_SYM_BITS){
+ _this->error|=ec_write_byte_at_end(_this,(unsigned)window&EC_SYM_MAX);
+ window>>=EC_SYM_BITS;
+ used-=EC_SYM_BITS;
+ }
+ /*Clear any excess space and add any remaining extra bits to the last byte.*/
+ if(!_this->error){
+ OPUS_CLEAR(_this->buf+_this->offs,
+ _this->storage-_this->offs-_this->end_offs);
+ if(used>0){
+ /*If there's no range coder data at all, give up.*/
+ if(_this->end_offs>=_this->storage)_this->error=-1;
+ else{
+ l=-l;
+ /*If we've busted, don't add too many extra bits to the last byte; it
+ would corrupt the range coder data, and that's more important.*/
+ if(_this->offs+_this->end_offs>=_this->storage&&l<used){
+ window&=(1<<l)-1;
+ _this->error=-1;
+ }
+ _this->buf[_this->storage-_this->end_offs-1]|=(unsigned char)window;
+ }
+ }
+ }
+}
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