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89 lines
2.9 KiB
89 lines
2.9 KiB
/*
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* Copyright 2020 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
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#define ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
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#include <math.h>
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#include <memory.h>
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#include <stdlib.h>
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#include "ManchesterEncoder.h"
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/**
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* Encode bytes using Manchester Code.
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* Round the edges using a half cosine to reduce ringing caused by a hard edge.
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*/
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class RoundedManchesterEncoder : public ManchesterEncoder {
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public:
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RoundedManchesterEncoder(int samplesPerPulse)
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: ManchesterEncoder(samplesPerPulse) {
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int rampSize = samplesPerPulse / 4;
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mZeroAfterZero = std::make_unique<float[]>(samplesPerPulse);
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mZeroAfterOne = std::make_unique<float[]>(samplesPerPulse);
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int sampleIndex = 0;
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for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
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float phase = (rampIndex + 1) * M_PI / rampSize;
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float sample = -cosf(phase);
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mZeroAfterZero[sampleIndex] = sample;
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mZeroAfterOne[sampleIndex] = 1.0f;
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sampleIndex++;
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}
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for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
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mZeroAfterZero[sampleIndex] = 1.0f;
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mZeroAfterOne[sampleIndex] = 1.0f;
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sampleIndex++;
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}
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for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
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float phase = (rampIndex + 1) * M_PI / rampSize;
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float sample = cosf(phase);
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mZeroAfterZero[sampleIndex] = sample;
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mZeroAfterOne[sampleIndex] = sample;
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sampleIndex++;
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}
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for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
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mZeroAfterZero[sampleIndex] = -1.0f;
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mZeroAfterOne[sampleIndex] = -1.0f;
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sampleIndex++;
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}
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}
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void onNextBit(bool current) override {
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// Do we need to use the rounded edge?
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mCurrentSamples = (current ^ mPreviousBit)
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? mZeroAfterOne.get()
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: mZeroAfterZero.get();
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mPreviousBit = current;
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}
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float nextFloat() override {
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advanceSample();
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float output = mCurrentSamples[mCursor];
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if (getCurrentBit()) output = -output;
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return output;
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}
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private:
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bool mPreviousBit = false;
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float *mCurrentSamples = nullptr;
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std::unique_ptr<float[]> mZeroAfterZero;
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std::unique_ptr<float[]> mZeroAfterOne;
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};
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#endif //ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
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