added polar code reliability sequence constructor

polar_sequence.hh

@@ -0,0 +1,40 @@
+/*
+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]; });
+	}
+};
+
+}
+