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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.
*/
#ifndef ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
#define ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
#include <math.h>
#include <memory>
#include <stdlib.h>
#include "ManchesterEncoder.h"
/**
* Encode bytes using Manchester Code.
* Round the edges using a half cosine to reduce ringing caused by a hard edge.
*/
class RoundedManchesterEncoder : public ManchesterEncoder {
public:
RoundedManchesterEncoder(int samplesPerPulse)
: ManchesterEncoder(samplesPerPulse) {
int rampSize = samplesPerPulse / 4;
mZeroAfterZero = std::make_unique<float[]>(samplesPerPulse);
mZeroAfterOne = std::make_unique<float[]>(samplesPerPulse);
int sampleIndex = 0;
for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
float phase = (rampIndex + 1) * M_PI / rampSize;
float sample = -cosf(phase);
mZeroAfterZero[sampleIndex] = sample;
mZeroAfterOne[sampleIndex] = 1.0f;
sampleIndex++;
}
for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
mZeroAfterZero[sampleIndex] = 1.0f;
mZeroAfterOne[sampleIndex] = 1.0f;
sampleIndex++;
}
for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
float phase = (rampIndex + 1) * M_PI / rampSize;
float sample = cosf(phase);
mZeroAfterZero[sampleIndex] = sample;
mZeroAfterOne[sampleIndex] = sample;
sampleIndex++;
}
for (int rampIndex = 0; rampIndex < rampSize; rampIndex++) {
mZeroAfterZero[sampleIndex] = -1.0f;
mZeroAfterOne[sampleIndex] = -1.0f;
sampleIndex++;
}
}
void onNextBit(bool current) override {
// Do we need to use the rounded edge?
mCurrentSamples = (current ^ mPreviousBit)
? mZeroAfterOne.get()
: mZeroAfterZero.get();
mPreviousBit = current;
}
float nextFloat() override {
advanceSample();
float output = mCurrentSamples[mCursor];
if (getCurrentBit()) output = -output;
return output;
}
private:
bool mPreviousBit = false;
float *mCurrentSamples = nullptr;
std::unique_ptr<float[]> mZeroAfterZero;
std::unique_ptr<float[]> mZeroAfterOne;
};
#endif //ANALYZER_ROUNDED_MANCHESTER_ENCODER_H
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