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/*
* Copyright 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <cassert>
#include "PolyphaseResamplerStereo.h"
using namespace RESAMPLER_OUTER_NAMESPACE::resampler;
#define STEREO 2
PolyphaseResamplerStereo::PolyphaseResamplerStereo(const MultiChannelResampler::Builder &builder)
: PolyphaseResampler(builder) {
assert(builder.getChannelCount() == STEREO);
}
void PolyphaseResamplerStereo::writeFrame(const float *frame) {
// Move cursor before write so that cursor points to last written frame in read.
if (--mCursor < 0) {
mCursor = getNumTaps() - 1;
}
float *dest = &mX[mCursor * STEREO];
const int offset = mNumTaps * STEREO;
// Write each channel twice so we avoid having to wrap when running the FIR.
const float left = frame[0];
const float right = frame[1];
// Put ordered writes together.
dest[0] = left;
dest[1] = right;
dest[offset] = left;
dest[1 + offset] = right;
}
void PolyphaseResamplerStereo::readFrame(float *frame) {
// Clear accumulators.
float left = 0.0;
float right = 0.0;
// Multiply input times precomputed windowed sinc function.
const float *coefficients = &mCoefficients[mCoefficientCursor];
float *xFrame = &mX[mCursor * STEREO];
const int numLoops = mNumTaps >> 2; // n/4
for (int i = 0; i < numLoops; i++) {
// Manual loop unrolling, might get converted to SIMD.
float coefficient = *coefficients++;
left += *xFrame++ * coefficient;
right += *xFrame++ * coefficient;
coefficient = *coefficients++; // next tap
left += *xFrame++ * coefficient;
right += *xFrame++ * coefficient;
coefficient = *coefficients++; // next tap
left += *xFrame++ * coefficient;
right += *xFrame++ * coefficient;
coefficient = *coefficients++; // next tap
left += *xFrame++ * coefficient;
right += *xFrame++ * coefficient;
}
mCoefficientCursor = (mCoefficientCursor + mNumTaps) % mCoefficients.size();
// Copy accumulators to output.
frame[0] = left;
frame[1] = right;
}
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