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replace x*155/100 by x*101581>>16

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Don't expect a visible speed diff. it's just cool.
(and, that's one less TODO in the code).

Change-Id: Iaeb2f1c930debb51501e170ee806f2f945fb1a8d
This commit is contained in:
Pascal Massimino 2012-07-23 14:21:30 -07:00
parent cbee59eba4
commit e45a446ad5
1 changed files with 4 additions and 2 deletions
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6
src/dec/quant.c
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@ -94,8 +94,10 @@ void VP8ParseQuant(VP8Decoder* const dec) {
m->y1_mat_[1] = kAcTable[clip(q + 0, 127)];
m->y2_mat_[0] = kDcTable[clip(q + dqy2_dc, 127)] * 2;
// TODO(skal): make it another table?
m->y2_mat_[1] = kAcTable[clip(q + dqy2_ac, 127)] * 155 / 100;
// For all x in [0..284], x*155/100 is bitwise equal to (x*101581) >> 16.
// The smallest precision for that is '(x*6349) >> 12' but 16 is a good
// word size.
m->y2_mat_[1] = (kAcTable[clip(q + dqy2_ac, 127)] * 101581) >> 16;
if (m->y2_mat_[1] < 8) m->y2_mat_[1] = 8;
m->uv_mat_[0] = kDcTable[clip(q + dquv_dc, 117)];