mediabunny/src/pcm.ts

// https://github.com/dystopiancode/pcm-g711/blob/master/pcm-g711/g711.c
export const toUlaw = (s16: number) => {
	const MULAW_MAX = 0x1FFF;
	const MULAW_BIAS = 33;

	let number = s16;
	let mask = 0x1000;
	let sign = 0;
	let position = 12;
	let lsb = 0;

	// Handle negative numbers
	if (number < 0) {
		number = -number;
		sign = 0x80;
	}

	// Add bias
	number += MULAW_BIAS;

	// Clip to maximum
	if (number > MULAW_MAX) {
		number = MULAW_MAX;
	}

	// Find position of first 1 in the number
	for (; ((number & mask) !== mask && position >= 5); mask >>= 1, position--) {
		// Empty loop body - all work done in condition
	}

	// Extract least significant bits
	lsb = (number >> (position - 4)) & 0x0f;

	// Combine sign, position and lsb, then invert all bits
	return ~(sign | ((position - 5) << 4) | lsb) & 0xFF;
};

export const fromUlaw = (u8: number) => {
	const MULAW_BIAS = 33;
	let sign = 0;
	let position = 0;

	// Get byte and invert
	let number = ~u8;

	// Handle sign
	if (number & 0x80) {
		number &= ~(1 << 7);
		sign = -1;
	}

	// Calculate position
	position = ((number & 0xF0) >> 4) + 5;

	// Reconstruct linear value
	const decoded = ((1 << position) | ((number & 0x0F) << (position - 4))
		| (1 << (position - 5))) - MULAW_BIAS;

	return (sign === 0) ? decoded : -decoded;
};

export const toAlaw = (s16: number) => {
	const ALAW_MAX = 0xFFF;
	let mask = 0x800;
	let sign = 0;
	let position = 11;
	let lsb = 0;

	let number = s16;

	// Handle negative numbers
	if (number < 0) {
		number = -number;
		sign = 0x80;
	}

	// Clip to maximum
	if (number > ALAW_MAX) {
		number = ALAW_MAX;
	}

	// Find position of first 1 in the number
	for (; ((number & mask) !== mask && position >= 5); mask >>= 1, position--) {
		// Empty loop body - all work done in condition
	}

	// Extract least significant bits
	lsb = (number >> ((position === 4) ? 1 : (position - 4))) & 0x0f;

	// Combine sign, position and lsb, then XOR with 0x55
	return (sign | ((position - 4) << 4) | lsb) ^ 0x55;
};

export const fromAlaw = (u8: number) => {
	let sign = 0x00;
	let position = 0;

	// Get byte and XOR with 0x55
	let number = u8 ^ 0x55;

	// Handle sign
	if (number & 0x80) {
		number &= ~(1 << 7);
		sign = -1;
	}

	// Calculate position
	position = ((number & 0xF0) >> 4) + 4;

	// Reconstruct linear value
	let decoded = 0;
	if (position !== 4) {
		decoded = ((1 << position) | ((number & 0x0F) << (position - 4))
			| (1 << (position - 5)));
	} else {
		decoded = (number << 1) | 1;
	}

	return (sign === 0) ? decoded : -decoded;
};