зеркало из https://github.com/mozilla/gecko-dev.git
61 строка
1.9 KiB
C++
61 строка
1.9 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef SINEWAVEGENERATOR_H_
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#define SINEWAVEGENERATOR_H_
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namespace mozilla {
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// generate 1k sine wave per second
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class SineWaveGenerator
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{
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public:
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static const int bytesPerSample = 2;
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static const int millisecondsPerSecond = PR_MSEC_PER_SEC;
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explicit SineWaveGenerator(uint32_t aSampleRate, uint32_t aFrequency) :
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mTotalLength(aSampleRate / aFrequency),
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mReadLength(0) {
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// If we allow arbitrary frequencies, there's no guarantee we won't get rounded here
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// We could include an error term and adjust for it in generation; not worth the trouble
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//MOZ_ASSERT(mTotalLength * aFrequency == aSampleRate);
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mAudioBuffer = MakeUnique<int16_t[]>(mTotalLength);
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for (int i = 0; i < mTotalLength; i++) {
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// Set volume to -20db. It's from 32768.0 * 10^(-20/20) = 3276.8
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mAudioBuffer[i] = (3276.8f * sin(2 * M_PI * i / mTotalLength));
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}
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}
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// NOTE: only safely called from a single thread (MSG callback)
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void generate(int16_t* aBuffer, int16_t aLengthInSamples) {
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int16_t remaining = aLengthInSamples;
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while (remaining) {
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int16_t processSamples = 0;
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if (mTotalLength - mReadLength >= remaining) {
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processSamples = remaining;
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} else {
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processSamples = mTotalLength - mReadLength;
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}
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memcpy(aBuffer, &mAudioBuffer[mReadLength], processSamples * bytesPerSample);
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aBuffer += processSamples;
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mReadLength += processSamples;
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remaining -= processSamples;
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if (mReadLength == mTotalLength) {
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mReadLength = 0;
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}
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}
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}
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private:
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UniquePtr<int16_t[]> mAudioBuffer;
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int16_t mTotalLength;
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int16_t mReadLength;
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};
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} // namespace mozilla
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#endif /* SINEWAVEGENERATOR_H_ */
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