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vorbisdec: ensure FASTDIV denominator is never 1

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In both usages of FASTDIV the denominator might be 1.

Using a branch could make the function slower than using a normal
division.

Both denominator and numerator can be multiplied by 2 safely and
using shifts is faster than using a branch.
This commit is contained in:
Luca Barbato 2012-09-13 19:45:21 +02:00
parent 44272c1ccc
commit 714508bcb9
1 changed files with 2 additions and 3 deletions
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5
libavcodec/vorbisdec.c
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@ -1354,8 +1354,7 @@ static av_always_inline int vorbis_residue_decode_internal(vorbis_context *vc,
if (vqbook >= 0 && vc->codebooks[vqbook].codevectors) {
unsigned coffs;
unsigned dim = vc->codebooks[vqbook].dimensions;
unsigned step = dim == 1 ? vr->partition_size
: FASTDIV(vr->partition_size, dim);
unsigned step = FASTDIV(vr->partition_size << 1, dim << 1);
vorbis_codebook codebook = vc->codebooks[vqbook];
if (vr_type == 0) {
@ -1409,7 +1408,7 @@ static av_always_inline int vorbis_residue_decode_internal(vorbis_context *vc,
}
} else if (vr_type == 2) {
unsigned voffs_div = FASTDIV(voffset, ch);
unsigned voffs_div = FASTDIV(voffset << 1, ch <<1);
unsigned voffs_mod = voffset - voffs_div * ch;
for (k = 0; k < step; ++k) {