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 "PolyphaseResamplerMono.h" 19 20 using namespace resampler; 21 22 #define MONO 1 23 PolyphaseResamplerMono(const MultiChannelResampler::Builder & builder)24PolyphaseResamplerMono::PolyphaseResamplerMono(const MultiChannelResampler::Builder &builder) 25 : PolyphaseResampler(builder) { 26 assert(builder.getChannelCount() == MONO); 27 } 28 writeFrame(const float * frame)29void PolyphaseResamplerMono::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 * MONO]; 35 const int offset = mNumTaps * MONO; 36 // Write each channel twice so we avoid having to wrap when running the FIR. 37 const float sample = frame[0]; 38 // Put ordered writes together. 39 dest[0] = sample; 40 dest[offset] = sample; 41 } 42 readFrame(float * frame)43void PolyphaseResamplerMono::readFrame(float *frame) { 44 // Clear accumulator. 45 float sum = 0.0; 46 47 // Multiply input times precomputed windowed sinc function. 48 const float *coefficients = &mCoefficients[mCoefficientCursor]; 49 float *xFrame = &mX[mCursor * MONO]; 50 const int numLoops = mNumTaps >> 2; // n/4 51 for (int i = 0; i < numLoops; i++) { 52 // Manual loop unrolling, might get converted to SIMD. 53 sum += *xFrame++ * *coefficients++; 54 sum += *xFrame++ * *coefficients++; 55 sum += *xFrame++ * *coefficients++; 56 sum += *xFrame++ * *coefficients++; 57 } 58 59 mCoefficientCursor = (mCoefficientCursor + mNumTaps) % mCoefficients.size(); 60 61 // Copy accumulator to output. 62 frame[0] = sum; 63 } 64