Source/WebCore/platform/audio/AudioUtilities.cpp

/*
 * Copyright (C) 2010, Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "AudioUtilities.h"
#include <wtf/MathExtras.h>

namespace WebCore {

namespace AudioUtilities {

double discreteTimeConstantForSampleRate(double timeConstant, double sampleRate)
{
    return 1 - exp(-1 / (sampleRate * timeConstant));
}

size_t timeToSampleFrame(double time, double sampleRate, SampleFrameRounding rounding)
{
    // To compute the desired frame number, we pretend we're actually running the
    // context at a much higher sample rate (by a factor of |oversampleFactor|).
    // Round this to get the nearest frame number at the higher rate. Then
    // convert back to the original rate to get a new frame number that may not be
    // an integer. Then use the specified |rounding_mode| to round this to the
    // integer frame number that we need.
    //
    // Doing this partially solves the issue where Fs * (k / Fs) != k when doing
    // floating point arithmtic for integer k and Fs is the sample rate. By
    // oversampling and rounding, we'll get k back most of the time.
    //
    // The oversampling factor MUST be a power of two so as not to introduce
    // additional round-off in computing the oversample frame number.
    constexpr double oversampleFactor = 1024;
    double frame = std::round(time * sampleRate * oversampleFactor) / oversampleFactor;

    switch (rounding) {
    case SampleFrameRounding::Nearest:
        frame = std::round(frame);
        break;
    case SampleFrameRounding::Down:
        frame = std::floor(frame);
        break;
    case SampleFrameRounding::Up:
        frame = std::ceil(frame);
        break;
    }

    // Just return the largest possible size_t value if necessary.
    if (frame >= std::numeric_limits<size_t>::max())
        return std::numeric_limits<size_t>::max();

    return static_cast<size_t>(frame);
}
} // AudioUtilites

} // WebCore

#endif // ENABLE(WEB_AUDIO)