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/*

Construct reliability sequences for polar codes

Copyright 2023 Ahmet Inan <inan@aicodix.de>

*/

#pragma once

#include <algorithm>

namespace CODE {

template <int MAX_M>

class PolarSeqConst0

{

void compute(double pe, int i, int h)

{

if (h) {

compute(pe * (2-pe), i, h/2);

compute(pe * pe, i+h, h/2);

} else {

prob[i] = pe;

}

}

double prob[1<<MAX_M];

int index[1<<MAX_M];

public:

void operator()(int *sequence, int level, double erasure_probability = std::exp(-1.))

{

assert(level <= MAX_M);

int length = 1 << level;

compute(erasure_probability, 0, length / 2);

for (int i = 0; i < length; ++i)

sequence[i] = i;

std::sort(sequence, sequence+length, [this](int a, int b){ return prob[a] > prob[b]; });

}

};

}