/* * 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 { 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)