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Change ec_{enc|dec}_bit_prob to take probabilities in units of 1/65536 instead of 1/256. This allows them to use a single 16x16->32 multiply instead of a 24x8->32 multiply. Also change the time-frequency resolution flag coding to ensure that "0" is always the most-probable symbol (i.e., that prob("1")<50%), as that's where all the rounding error accumulates.

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Timothy B. Terriberry 2010-05-29 23:02:33 -04:00 • committed by Jean-Marc Valin
parent 299747ee24
commit 43e9406201
5 changed files with 14 additions and 14 deletions
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8
libcelt/celt.c
View file

@ -615,11 +615,11 @@ static void tf_encode(celt_word16 *bandLogE, celt_word16 *oldBandE, int len, int
else
tf_res[i] = path0[i+1];
}
ec_enc_bit_prob(enc, tf_res[0], isTransient ? 64 : 16);
ec_enc_bit_prob(enc, tf_res[0], isTransient ? 16384 : 4096);
curr = tf_res[0];
for (i=1;i<len;i++)
{
ec_enc_bit_prob(enc, tf_res[i], curr ? 240: 16);
ec_enc_bit_prob(enc, tf_res[i] ^ curr, 4096);
curr = tf_res[i];
}
RESTORE_STACK
@ -629,11 +629,11 @@ static void tf_decode(int len, int C, int isTransient, int *tf_res, ec_dec *dec)
{
int i, curr;
tf_res[0] = ec_dec_bit_prob(dec, isTransient ? 64 : 16);
tf_res[0] = ec_dec_bit_prob(dec, isTransient ? 16384 : 4096);
curr = tf_res[0];
for (i=1;i<len;i++)
{
tf_res[i] = ec_dec_bit_prob(dec, curr ? 240: 16);
tf_res[i] = ec_dec_bit_prob(dec, 4096) ^ curr;
curr = tf_res[i];
}
}

4
libcelt/entdec.h
View file

@ -110,8 +110,8 @@ ec_uint32 ec_dec_bits(ec_dec *_this,int _ftb);
Return: The decoded bits.*/
ec_uint32 ec_dec_uint(ec_dec *_this,ec_uint32 _ft);
/* Decode a bit that has a _prob/256 probability of being a one */
int ec_dec_bit_prob(ec_dec *_this,int _prob);
/* Decode a bit that has a _prob/65536 probability of being a one */
int ec_dec_bit_prob(ec_dec *_this,unsigned _prob);
/*Returns the number of bits "used" by the decoded symbols so far.
The actual number of bits may be larger, due to rounding to whole bytes, or

4
libcelt/entenc.h
View file

@ -91,8 +91,8 @@ void ec_enc_bits(ec_enc *_this,ec_uint32 _fl,int _ftb);
This must be at least one, and no more than 2**32-1.*/
void ec_enc_uint(ec_enc *_this,ec_uint32 _fl,ec_uint32 _ft);
/* Encode a bit that has a _prob/256 probability of being a one */
void ec_enc_bit_prob(ec_enc *_this,int val,int _prob);
/* Encode a bit that has a _prob/65536 probability of being a one */
void ec_enc_bit_prob(ec_enc *_this,int val,unsigned _prob);
/*Returns the number of bits "used" by the encoded symbols so far.
The actual number of bits may be larger, due to rounding to whole bytes, or

6
libcelt/rangedec.c
View file

@ -186,15 +186,15 @@ void ec_dec_update(ec_dec *_this,unsigned _fl,unsigned _fh,unsigned _ft){
ec_dec_normalize(_this);
}
/*The probability of having a "one" is given in 1/256.*/
int ec_dec_bit_prob(ec_dec *_this,int _prob){
/*The probability of having a "one" is given in 1/65536.*/
int ec_dec_bit_prob(ec_dec *_this,unsigned _prob){
ec_uint32 r;
ec_uint32 s;
ec_uint32 d;
int val;
r=_this->rng;
d=_this->dif;
s=IMUL32(r>>8,_prob);
s=(r>>16)*_prob;
val=d<=s;
if(!val)_this->dif=d-s;
_this->rng=val?s:r-s;

6
libcelt/rangeenc.c
View file

@ -138,14 +138,14 @@ void ec_encode_bin(ec_enc *_this,unsigned _fl,unsigned _fh,unsigned _bits){
ec_enc_normalize(_this);
}
/*The probability of having a "one" is given in 1/256.*/
void ec_enc_bit_prob(ec_enc *_this,int _val,int _prob){
/*The probability of having a "one" is given in 1/65536.*/
void ec_enc_bit_prob(ec_enc *_this,int _val,unsigned _prob){
ec_uint32 r;
ec_uint32 s;
ec_uint32 l;
r=_this->rng;
l=_this->low;
s=IMUL32(r>>8,_prob);
s=(r>>16)*_prob;
r-=s;
if(_val)_this->low=l+r;
_this->rng=_val?s:r;