path: root/Source/WebCore/platform/audio/SincResampler.cpp

/*
 * Copyright (C) 2011 Google Inc. All rights reserved.
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#include "config.h"

#if ENABLE(WEB_AUDIO)

#include "SincResampler.h"

#include <wtf/MathExtras.h>

using namespace std;

// Input buffer layout, dividing the total buffer into regions (r0 - r5):
//
// |----------------|----------------------------------------------------------------|----------------|
//
//                                              blockSize + kernelSize / 2                           
//                   <-------------------------------------------------------------------------------->
//                                                  r0
//
//   kernelSize / 2   kernelSize / 2                                 kernelSize / 2     kernelSize / 2 
// <---------------> <--------------->                              <---------------> <--------------->
//         r1                r2                                             r3                r4
// 
//                                              blockSize                           
//                                     <-------------------------------------------------------------->
//                                                  r5

// The Algorithm:
//
// 1) Consume input frames into r0 (r1 is zero-initialized).
// 2) Position kernel centered at start of r0 (r2) and generate output frames until kernel is centered at start of r4.
//    or we've finished generating all the output frames.
// 3) Copy r3 to r1 and r4 to r2.
// 4) Consume input frames into r5 (zero-pad if we run out of input).
// 5) Goto (2) until all of input is consumed.
//
// note: we're glossing over how the sub-sample handling works with m_virtualSourceIndex, etc.

namespace WebCore {

SincResampler::SincResampler(double scaleFactor, unsigned kernelSize, unsigned numberOfKernelOffsets)
    : m_scaleFactor(scaleFactor)
    , m_kernelSize(kernelSize)
    , m_numberOfKernelOffsets(numberOfKernelOffsets)
    , m_kernelStorage(m_kernelSize * (m_numberOfKernelOffsets + 1))
    , m_virtualSourceIndex(0.0)
    , m_blockSize(512)
    , m_inputBuffer(m_blockSize + m_kernelSize) // See input buffer layout above.
    , m_source(0)
    , m_sourceFramesAvailable(0)
{
    initializeKernel();
}

void SincResampler::initializeKernel()
{
    // Blackman window parameters.
    double alpha = 0.16;
    double a0 = 0.5 * (1.0 - alpha);
    double a1 = 0.5;
    double a2 = 0.5 * alpha;

    // sincScaleFactor is basically the normalized cutoff frequency of the low-pass filter.
    double sincScaleFactor = m_scaleFactor > 1.0 ? 1.0 / m_scaleFactor : 1.0;

    // The sinc function is an idealized brick-wall filter, but since we're windowing it the
    // transition from pass to stop does not happen right away. So we should adjust the
    // lowpass filter cutoff slightly downward to avoid some aliasing at the very high-end.
    // FIXME: this value is empirical and to be more exact should vary depending on m_kernelSize.
    sincScaleFactor *= 0.9;

    int n = m_kernelSize;
    int halfSize = n / 2;

    // Generates a set of windowed sinc() kernels.
    // We generate a range of sub-sample offsets from 0.0 to 1.0.
    for (unsigned offsetIndex = 0; offsetIndex <= m_numberOfKernelOffsets; ++offsetIndex) {
        double subsampleOffset = static_cast<double>(offsetIndex) / m_numberOfKernelOffsets;

        for (int i = 0; i < n; ++i) {
            // Compute the sinc() with offset.
            double s = sincScaleFactor * piDouble * (i - halfSize - subsampleOffset);
            double sinc = !s ? 1.0 : sin(s) / s;
            sinc *= sincScaleFactor;

            // Compute Blackman window, matching the offset of the sinc().
            double x = (i - subsampleOffset) / n;
            double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x);

            // Window the sinc() function and store at the correct offset.
            m_kernelStorage[i + offsetIndex * m_kernelSize] = sinc * window;
        }
    }
}

void SincResampler::consumeSource(float* buffer, unsigned numberOfSourceFrames)
{
    ASSERT(m_source);
    if (!m_source)
        return;
    
    // Clamp to number of frames available and zero-pad.
    unsigned framesToCopy = min(m_sourceFramesAvailable, numberOfSourceFrames);
    memcpy(buffer, m_source, sizeof(float) * framesToCopy);
    
    // Zero-pad if necessary.
    if (framesToCopy < numberOfSourceFrames)
        memset(buffer + framesToCopy, 0, sizeof(float) * (numberOfSourceFrames - framesToCopy));
    
    m_sourceFramesAvailable -= framesToCopy;
    m_source += numberOfSourceFrames;
}

void SincResampler::process(float* source, float* destination, unsigned numberOfSourceFrames)
{
    ASSERT(m_blockSize > m_kernelSize);
    ASSERT(m_inputBuffer.size() >= m_blockSize + m_kernelSize);
    ASSERT(!(m_kernelSize % 2));
    
    // Setup various region pointers in the buffer (see diagram above).
    float* r0 = m_inputBuffer.data() + m_kernelSize / 2;
    float* r1 = m_inputBuffer.data();
    float* r2 = r0;
    float* r3 = r0 + m_blockSize - m_kernelSize / 2;
    float* r4 = r0 + m_blockSize;
    float* r5 = r0 + m_kernelSize / 2;

    m_source = source;
    m_sourceFramesAvailable = numberOfSourceFrames;

    unsigned numberOfDestinationFrames = static_cast<unsigned>(numberOfSourceFrames / m_scaleFactor);

    // Step (1)
    // Prime the input buffer.
    consumeSource(r0, m_blockSize + m_kernelSize / 2);
    
    // Step (2)
    m_virtualSourceIndex = 0;

    while (numberOfDestinationFrames) {
        while (m_virtualSourceIndex < m_blockSize) {
            // m_virtualSourceIndex lies in between two kernel offsets so figure out what they are.
            int sourceIndexI = static_cast<int>(m_virtualSourceIndex);
            double subsampleRemainder = m_virtualSourceIndex - sourceIndexI;

            double virtualOffsetIndex = subsampleRemainder * m_numberOfKernelOffsets;
            int offsetIndex = static_cast<int>(virtualOffsetIndex);
            
            float* k1 = m_kernelStorage.data() + offsetIndex * m_kernelSize;
            float* k2 = k1 + m_kernelSize;

            // Initialize input pointer based on quantized m_virtualSourceIndex.
            float* inputP = r1 + sourceIndexI;

            // We'll compute "convolutions" for the two kernels which straddle m_virtualSourceIndex
            float sum1 = 0;
            float sum2 = 0;

            // Figure out how much to weight each kernel's "convolution".
            double kernelInterpolationFactor = virtualOffsetIndex - offsetIndex;

            // Generate a single output sample. 
            int n = m_kernelSize;

            // FIXME: add SIMD optimizations for the following. The scalar code-path can probably also be optimized better.

#define CONVOLVE_ONE_SAMPLE      \
            input = *inputP++;   \
            sum1 += input * *k1; \
            sum2 += input * *k2; \
            ++k1;                \
            ++k2;

            {
                float input;
                
                // Optimize size 32 and size 64 kernels by unrolling the while loop.
                // A 20 - 30% speed improvement was measured in some cases by using this approach.
                
                if (n == 32) {
                    CONVOLVE_ONE_SAMPLE // 1
                    CONVOLVE_ONE_SAMPLE // 2
                    CONVOLVE_ONE_SAMPLE // 3
                    CONVOLVE_ONE_SAMPLE // 4
                    CONVOLVE_ONE_SAMPLE // 5
                    CONVOLVE_ONE_SAMPLE // 6
                    CONVOLVE_ONE_SAMPLE // 7
                    CONVOLVE_ONE_SAMPLE // 8
                    CONVOLVE_ONE_SAMPLE // 9
                    CONVOLVE_ONE_SAMPLE // 10
                    CONVOLVE_ONE_SAMPLE // 11
                    CONVOLVE_ONE_SAMPLE // 12
                    CONVOLVE_ONE_SAMPLE // 13
                    CONVOLVE_ONE_SAMPLE // 14
                    CONVOLVE_ONE_SAMPLE // 15
                    CONVOLVE_ONE_SAMPLE // 16
                    CONVOLVE_ONE_SAMPLE // 17
                    CONVOLVE_ONE_SAMPLE // 18
                    CONVOLVE_ONE_SAMPLE // 19
                    CONVOLVE_ONE_SAMPLE // 20
                    CONVOLVE_ONE_SAMPLE // 21
                    CONVOLVE_ONE_SAMPLE // 22
                    CONVOLVE_ONE_SAMPLE // 23
                    CONVOLVE_ONE_SAMPLE // 24
                    CONVOLVE_ONE_SAMPLE // 25
                    CONVOLVE_ONE_SAMPLE // 26
                    CONVOLVE_ONE_SAMPLE // 27
                    CONVOLVE_ONE_SAMPLE // 28
                    CONVOLVE_ONE_SAMPLE // 29
                    CONVOLVE_ONE_SAMPLE // 30
                    CONVOLVE_ONE_SAMPLE // 31
                    CONVOLVE_ONE_SAMPLE // 32
                } else if (n == 64) {
                    CONVOLVE_ONE_SAMPLE // 1
                    CONVOLVE_ONE_SAMPLE // 2
                    CONVOLVE_ONE_SAMPLE // 3
                    CONVOLVE_ONE_SAMPLE // 4
                    CONVOLVE_ONE_SAMPLE // 5
                    CONVOLVE_ONE_SAMPLE // 6
                    CONVOLVE_ONE_SAMPLE // 7
                    CONVOLVE_ONE_SAMPLE // 8
                    CONVOLVE_ONE_SAMPLE // 9
                    CONVOLVE_ONE_SAMPLE // 10
                    CONVOLVE_ONE_SAMPLE // 11
                    CONVOLVE_ONE_SAMPLE // 12
                    CONVOLVE_ONE_SAMPLE // 13
                    CONVOLVE_ONE_SAMPLE // 14
                    CONVOLVE_ONE_SAMPLE // 15
                    CONVOLVE_ONE_SAMPLE // 16
                    CONVOLVE_ONE_SAMPLE // 17
                    CONVOLVE_ONE_SAMPLE // 18
                    CONVOLVE_ONE_SAMPLE // 19
                    CONVOLVE_ONE_SAMPLE // 20
                    CONVOLVE_ONE_SAMPLE // 21
                    CONVOLVE_ONE_SAMPLE // 22
                    CONVOLVE_ONE_SAMPLE // 23
                    CONVOLVE_ONE_SAMPLE // 24
                    CONVOLVE_ONE_SAMPLE // 25
                    CONVOLVE_ONE_SAMPLE // 26
                    CONVOLVE_ONE_SAMPLE // 27
                    CONVOLVE_ONE_SAMPLE // 28
                    CONVOLVE_ONE_SAMPLE // 29
                    CONVOLVE_ONE_SAMPLE // 30
                    CONVOLVE_ONE_SAMPLE // 31
                    CONVOLVE_ONE_SAMPLE // 32
                    CONVOLVE_ONE_SAMPLE // 33
                    CONVOLVE_ONE_SAMPLE // 34
                    CONVOLVE_ONE_SAMPLE // 35
                    CONVOLVE_ONE_SAMPLE // 36
                    CONVOLVE_ONE_SAMPLE // 37
                    CONVOLVE_ONE_SAMPLE // 38
                    CONVOLVE_ONE_SAMPLE // 39
                    CONVOLVE_ONE_SAMPLE // 40
                    CONVOLVE_ONE_SAMPLE // 41
                    CONVOLVE_ONE_SAMPLE // 42
                    CONVOLVE_ONE_SAMPLE // 43
                    CONVOLVE_ONE_SAMPLE // 44
                    CONVOLVE_ONE_SAMPLE // 45
                    CONVOLVE_ONE_SAMPLE // 46
                    CONVOLVE_ONE_SAMPLE // 47
                    CONVOLVE_ONE_SAMPLE // 48
                    CONVOLVE_ONE_SAMPLE // 49
                    CONVOLVE_ONE_SAMPLE // 50
                    CONVOLVE_ONE_SAMPLE // 51
                    CONVOLVE_ONE_SAMPLE // 52
                    CONVOLVE_ONE_SAMPLE // 53
                    CONVOLVE_ONE_SAMPLE // 54
                    CONVOLVE_ONE_SAMPLE // 55
                    CONVOLVE_ONE_SAMPLE // 56
                    CONVOLVE_ONE_SAMPLE // 57
                    CONVOLVE_ONE_SAMPLE // 58
                    CONVOLVE_ONE_SAMPLE // 59
                    CONVOLVE_ONE_SAMPLE // 60
                    CONVOLVE_ONE_SAMPLE // 61
                    CONVOLVE_ONE_SAMPLE // 62
                    CONVOLVE_ONE_SAMPLE // 63
                    CONVOLVE_ONE_SAMPLE // 64
                } else {
                    while (n--) {
                        // Non-optimized using actual while loop.
                        CONVOLVE_ONE_SAMPLE
                    }
                }
            }

            // Linearly interpolate the two "convolutions".
            double result = (1.0 - kernelInterpolationFactor) * sum1 + kernelInterpolationFactor * sum2;

            *destination++ = result;

            --numberOfDestinationFrames;
            if (!numberOfDestinationFrames)
                return;

            // Advance the virtual index.
            m_virtualSourceIndex += m_scaleFactor;
        }

        // Wrap back around to the start.
        m_virtualSourceIndex -= m_blockSize;

        // Step (3) Copy r3 to r1 and r4 to r2.
        // This wraps the last input frames back to the start of the buffer.
        memcpy(r1, r3, sizeof(float) * (m_kernelSize / 2));
        memcpy(r2, r4, sizeof(float) * (m_kernelSize / 2));

        // Step (4)
        // Refresh the buffer with more input.
        consumeSource(r5, m_blockSize);
    }
}

} // namespace WebCore

#endif // ENABLE(WEB_AUDIO)