ref: d69c1cb37c0b88febe74656feeaa067cc09f9add
dir: /libcelt/mfrngenc.c/
/* Copyright (c) 2001-2008 Timothy B. Terriberry
Copyright (c) 2008 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.
- Neither the name of the Xiph.org Foundation nor the names of its
contributors may be used to endorse or promote products derived from
this software without specific prior written permission.
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 FOUNDATION 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 "arch.h"
#include "entenc.h"
#include "mfrngcod.h"
/*A multiply-free range encoder.
See mfrngdec.c and the references for implementation details
\cite{Mar79,MNW98,SM98}.
@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"
}
@INPROCEEDINGS{SM98,
author="Lang Stuiver and Alistair Moffat",
title="Piecewise Integer Mapping for Arithmetic Coding",
booktitle="Proceedings of the {IEEE} Data Compression Conference",
pages="1--10",
address="Snowbird, UT",
month="Mar./Apr.",
year=1998
}*/
/*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)ec_byte_write1(_this->buf,_this->rem+carry);
if(_this->ext>0){
unsigned sym;
sym=EC_SYM_MAX+carry&EC_SYM_MAX;
do ec_byte_write1(_this->buf,sym);
while(--(_this->ext)>0);
}
_this->rem=_c&EC_SYM_MAX;
}
else _this->ext++;
}
static 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->low>>EC_CODE_SHIFT));
/*Move the next-to-high-order symbol into the high-order position.*/
_this->low=_this->low<<EC_SYM_BITS&EC_CODE_TOP-1;
_this->rng<<=EC_SYM_BITS;
}
}
void ec_enc_init(ec_enc *_this,ec_byte_buffer *_buf){
_this->buf=_buf;
_this->rem=-1;
_this->ext=0;
_this->low=0;
_this->rng=EC_CODE_TOP;
_this->end_byte=0;
_this->end_bits_left=8;
_this->nb_end_bits=0;
}
void ec_encode(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _ft){
ec_uint32 fl;
ec_uint32 fh;
ec_uint32 ft;
ec_uint32 r;
ec_uint32 s;
ec_uint32 d;
int e;
int nrm;
/*Step 1: we want ft in the range of [rng/2,rng).
The high-order bits of the rng and ft are computed via a logarithm.
This could also be done on some architectures with some custom assembly,
which would provide even more speed.*/
nrm=EC_ILOG(_this->rng)-EC_ILOG(_ft);
/*Having the same high order bit may be too much.
We may need to shift one less to ensure that ft is actually in the proper
range.*/
ft=(ec_uint32)_ft<<nrm;
e=ft>_this->rng;
ft>>=e;
nrm-=e;
/*We then scale everything by the computed power of 2.*/
fl=(ec_uint32)_fl<<nrm;
fh=(ec_uint32)_fh<<nrm;
/*Step 2: compute the two values of the partition function.
d is the splitting point of the interval [0,ft).*/
d=_this->rng-ft;
r=fh+EC_MINI(fh,d);
s=fl+EC_MINI(fl,d);
/*Step 3: Update the end-point and range of the interval.*/
_this->low+=s;
_this->rng=r-s;
/*Step 4: Normalize the interval.*/
ec_enc_normalize(_this);
}
void ec_encode_bin(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned bits){
#if 0
ec_encode(_this, _fl, _fh, 1U<<bits);
#else
_this->nb_end_bits += bits;
while (bits >= _this->end_bits_left)
{
_this->end_byte |= (_fl<<(8-_this->end_bits_left)) & 0xff;
_fl >>= _this->end_bits_left;
ec_byte_write_at_end(_this->buf, _this->end_byte);
_this->end_byte = 0;
bits -= _this->end_bits_left;
_this->end_bits_left = 8;
}
_this->end_byte |= (_fl<<(8-_this->end_bits_left)) & 0xff;
_this->end_bits_left -= bits;
#endif
}
long ec_enc_tell(ec_enc *_this,int _b){
ec_uint32 r;
int l;
long nbits;
nbits=(ec_byte_bytes(_this->buf)+(_this->rem>=0)+_this->ext)*EC_SYM_BITS;
/*To handle the non-integral number of bits still left in the encoder state,
we compute the number of bits of low that must be encoded to ensure that
the value is inside the range for any possible subsequent bits.*/
nbits+=EC_CODE_BITS+1+_this->nb_end_bits;
nbits<<=_b;
l=EC_ILOG(_this->rng);
r=_this->rng>>l-16;
while(_b-->0){
int b;
r=r*r>>15;
b=(int)(r>>16);
l=l<<1|b;
r>>=b;
}
return nbits-l;
}
void ec_enc_done(ec_enc *_this){
ec_uint32 end;
ec_uint32 msk;
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->low+msk&~msk;
if((end|msk)>=_this->low+_this->rng){
l++;
msk>>=1;
end=_this->low+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);
_this->rem=-1;
}
{
unsigned char *ptr = _this->buf->ptr;
while (ptr<= _this->buf->end_ptr)
*ptr++ = 0;
if (_this->end_bits_left != 8)
*_this->buf->end_ptr |= _this->end_byte;
}
}