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/*
* Copyright (C) 2010, Google Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
* ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "config.h"
#if ENABLE(WEB_AUDIO)
#include "AudioUtilities.h"
#include <wtf/MathExtras.h>
namespace WebCore {
namespace AudioUtilities {
float decibelsToLinear(float decibels)
{
return powf(10, 0.05f * decibels);
}
float linearToDecibels(float linear)
{
// It's not possible to calculate decibels for a zero linear value since it would be -Inf.
// -1000.0 dB represents a very tiny linear value in case we ever reach this case.
ASSERT(linear);
if (!linear)
return -1000;
return 20 * log10f(linear);
}
float discreteTimeConstantForSampleRate(float timeConstant, float sampleRate)
{
// hardcoded value is temporary build fix for Windows.
// FIXME: replace hardcode 2.718282 with M_E until the correct MathExtras.h solution is determined.
return 1 - powf(1 / 2.718282f, 1 / (sampleRate * timeConstant));
}
#if OS(WINDOWS) && COMPILER(MSVC) && !_M_IX86_FP
// When compiling with MSVC with x87 FPU instructions using 80-bit
// floats, we want very precise control over the arithmetic so that
// rounding is done according to the IEEE 754 specification for
// single- and double-precision floats. We want each operation to be
// done with specified arithmetic precision and rounding consistent
// with gcc, not extended to 80 bits automatically.
//
// These pragmas are equivalent to /fp:strict flag, but we only need
// it for the function here. (Using fp:strict everywhere can have
// severe impact on floating point performance.)
#pragma float_control(push)
#pragma float_control(precise, on)
#pragma fenv_access(on)
#pragma float_control(except, on)
#endif
size_t timeToSampleFrame(double time, double sampleRate)
{
// DO NOT CONSOLIDATE THESE ASSIGNMENTS INTO ONE! When compiling
// with Visual Studio, these assignments force the rounding of
// each operation according to IEEE 754, instead of leaving
// intermediate results in 80-bit precision which is not
// consistent with IEEE 754 double-precision rounding.
double r = time * sampleRate;
r += 0.5;
return static_cast<size_t>(r);
}
#if OS(WINDOWS) && COMPILER(MSVC) && !_M_IX86_FP
// Restore normal floating-point semantics.
#pragma float_control(pop)
#endif
} // AudioUtilites
} // WebCore
#endif // ENABLE(WEB_AUDIO)
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