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unroll finite differences to avoid swapping registers.

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1.5x faster encode_residual_fixed().
overall flac encoding: 3% faster at compression_levels 0-2.

Originally committed as revision 10625 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Loren Merritt 2007-09-29 23:44:34 +00:00
parent a309dce75f
commit bfdd5bc1f1
1 changed files with 12 additions and 9 deletions
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21
libavcodec/flacenc.c
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@ -841,33 +841,36 @@ static void encode_residual_fixed(int32_t *res, const int32_t *smp, int n,
res[i]= smp[i] - smp[i-1];
}else if(order==2){
int a = smp[order-1] - smp[order-2];
for(i=order; i<n; i++) {
for(i=order; i<n; i+=2) {
int b = smp[i] - smp[i-1];
res[i]= b - a;
a = b;
a = smp[i+1] - smp[i];
res[i+1]= a - b;
}
}else if(order==3){
int a = smp[order-1] - smp[order-2];
int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
for(i=order; i<n; i++) {
for(i=order; i<n; i+=2) {
int b = smp[i] - smp[i-1];
int d = b - a;
res[i]= d - c;
a = b;
c = d;
a = smp[i+1] - smp[i];
c = a - b;
res[i+1]= c - d;
}
}else{
int a = smp[order-1] - smp[order-2];
int c = smp[order-1] - 2*smp[order-2] + smp[order-3];
int e = smp[order-1] - 3*smp[order-2] + 3*smp[order-3] - smp[order-4];
for(i=order; i<n; i++) {
for(i=order; i<n; i+=2) {
int b = smp[i] - smp[i-1];
int d = b - a;
int f = d - c;
res[i]= f - e;
a = b;
c = d;
e = f;
a = smp[i+1] - smp[i];
c = a - b;
e = c - d;
res[i+1]= e - f;
}
}
}