1 /* 2 * Copyright 2019 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include <cassert> 18 #include "PolyphaseResamplerStereo.h" 19 20 using namespace resampler; 21 22 #define STEREO 2 23 PolyphaseResamplerStereo(const MultiChannelResampler::Builder & builder)24PolyphaseResamplerStereo::PolyphaseResamplerStereo(const MultiChannelResampler::Builder &builder) 25 : PolyphaseResampler(builder) { 26 assert(builder.getChannelCount() == STEREO); 27 } 28 writeFrame(const float * frame)29void PolyphaseResamplerStereo::writeFrame(const float *frame) { 30 // Move cursor before write so that cursor points to last written frame in read. 31 if (--mCursor < 0) { 32 mCursor = getNumTaps() - 1; 33 } 34 float *dest = &mX[mCursor * STEREO]; 35 const int offset = mNumTaps * STEREO; 36 // Write each channel twice so we avoid having to wrap when running the FIR. 37 const float left = frame[0]; 38 const float right = frame[1]; 39 // Put ordered writes together. 40 dest[0] = left; 41 dest[1] = right; 42 dest[offset] = left; 43 dest[1 + offset] = right; 44 } 45 readFrame(float * frame)46void PolyphaseResamplerStereo::readFrame(float *frame) { 47 // Clear accumulators. 48 float left = 0.0; 49 float right = 0.0; 50 51 // Multiply input times precomputed windowed sinc function. 52 const float *coefficients = &mCoefficients[mCoefficientCursor]; 53 float *xFrame = &mX[mCursor * STEREO]; 54 const int numLoops = mNumTaps >> 2; // n/4 55 for (int i = 0; i < numLoops; i++) { 56 // Manual loop unrolling, might get converted to SIMD. 57 float coefficient = *coefficients++; 58 left += *xFrame++ * coefficient; 59 right += *xFrame++ * coefficient; 60 61 coefficient = *coefficients++; // next tap 62 left += *xFrame++ * coefficient; 63 right += *xFrame++ * coefficient; 64 65 coefficient = *coefficients++; // next tap 66 left += *xFrame++ * coefficient; 67 right += *xFrame++ * coefficient; 68 69 coefficient = *coefficients++; // next tap 70 left += *xFrame++ * coefficient; 71 right += *xFrame++ * coefficient; 72 } 73 74 mCoefficientCursor = (mCoefficientCursor + mNumTaps) % mCoefficients.size(); 75 76 // Copy accumulators to output. 77 frame[0] = left; 78 frame[1] = right; 79 } 80