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b=1012609 improve PeriodicWave phase-wrapping logic r=rillian

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This approach takes advantage of the fact that periodicWaveSize is a power of
2 and uses unsigned integer modulo arithmetic to find the appropriate phase
of the period.

--HG--
extra : rebase_source : bb5fc413785d5f12a76cff4cbb5ba2ed5e979b41
This commit is contained in:
Karl Tomlinson 2014-09-30 18:10:03 +13:00
parent 97db07c4dd
commit 1935e660b0
1 changed files with 15 additions and 7 deletions
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22
content/media/webaudio/OscillatorNode.cpp
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@ -373,6 +373,10 @@ public:
MOZ_ASSERT(mPeriodicWave, "No custom waveform data");
uint32_t periodicWaveSize = mPeriodicWave->periodicWaveSize();
// Mask to wrap wave data indices into the range [0,periodicWaveSize).
uint32_t indexMask = periodicWaveSize - 1;
MOZ_ASSERT(periodicWaveSize && (periodicWaveSize & indexMask) == 0,
"periodicWaveSize must be power of 2");
float* higherWaveData = nullptr;
float* lowerWaveData = nullptr;
float tableInterpolationFactor;
@ -387,14 +391,15 @@ public:
lowerWaveData,
higherWaveData,
tableInterpolationFactor);
mPhase = fmod(mPhase, periodicWaveSize);
// Bilinear interpolation between adjacent samples in each table.
uint32_t j1 = floor(mPhase);
float floorPhase = floorf(mPhase);
uint32_t j1 = floorPhase;
j1 &= indexMask;
uint32_t j2 = j1 + 1;
if (j2 >= periodicWaveSize) {
j2 -= periodicWaveSize;
}
float sampleInterpolationFactor = mPhase - j1;
j2 &= indexMask;
float sampleInterpolationFactor = mPhase - floorPhase;
float lower = (1.0f - sampleInterpolationFactor) * lowerWaveData[j1] +
sampleInterpolationFactor * lowerWaveData[j2];
float higher = (1.0f - sampleInterpolationFactor) * higherWaveData[j1] +
@ -402,7 +407,10 @@ public:
aOutput[i] = (1.0f - tableInterpolationFactor) * lower +
tableInterpolationFactor * higher;
mPhase += basePhaseIncrement * mFinalFrequency;
// Calculate next phase position from wrapped value j1 to avoid loss of
// precision at large values.
mPhase =
j1 + sampleInterpolationFactor + basePhaseIncrement * mFinalFrequency;
}
}