add a-law companding functions

companding/alaw.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <cmath>
+
+namespace trnr {
+
+constexpr float A_LAW_A = 87.6f;
+
+inline float alaw_encode(float input)
+{
+	float sign = (input >= 0.0f) ? 1.0f : -1.0f;
+	float abs_sample = std::fabs(input);
+
+	float output;
+	if (abs_sample < (1.0f / A_LAW_A)) {
+		output = sign * (A_LAW_A * abs_sample) / (1.0f + std::log(A_LAW_A));
+	} else {
+		output = sign * (1.0f + std::log(A_LAW_A * abs_sample)) / (1.0f + std::log(A_LAW_A));
+	}
+
+	return output;
+}
+
+inline float alaw_decode(float input)
+{
+	float sign = (input >= 0.0f) ? 1.0f : -1.0f;
+	float abs_comp = std::fabs(input);
+
+	float sample;
+	if (abs_comp < (1.0f / (1.0f + std::log(A_LAW_A)))) {
+		sample = sign * (abs_comp * (1.0f + std::log(A_LAW_A))) / A_LAW_A;
+	} else {
+		sample = sign * std::exp(abs_comp * (1.0f + std::log(A_LAW_A)) - 1.0f) / A_LAW_A;
+	}
+
+	return sample;
+}
+} // namespace trnr