alawmulaw/lib/mulaw.js

/*
 * alawmulaw: A-Law and mu-Law codecs in JavaScript.
 * https://github.com/rochars/alawmulaw
 *
 * Copyright (c) 2018 Rafael da Silva Rocha.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 */

/**
 * @fileoverview mu-Law codec.
 */

/** @module alawmulaw/mulaw */

/**
 * @type {number}
 * @private
 */
const BIAS = 0x84;
/**
 * @type {number}
 * @private
 */
const CLIP = 32635;
/**
 * @type {Array<number>}
 * @private
 */
const encodeTable = [
    0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
    4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
    5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
    5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
    6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
    6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
    6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
    6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
    7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7];
/**
 * @type {Array<number>}
 * @private
 */
const decodeTable = [0,132,396,924,1980,4092,8316,16764];

/**
 * Encode a 16-bit linear PCM sample as 8-bit mu-Law.
 * @param {number} sample A 16-bit PCM sample
 * @return {number}
 */
export function encodeSample(sample) {
  /** @type {number} */
  let sign;
  /** @type {number} */
  let exponent;
  /** @type {number} */
  let mantissa;
  /** @type {number} */
  let muLawSample;
  /** get the sample into sign-magnitude **/
  sign = (sample >> 8) & 0x80;
  if (sign != 0) sample = -sample;
  if (sample > CLIP) sample = CLIP;
  /** convert from 16 bit linear to ulaw **/
  sample = sample + BIAS;
  exponent = encodeTable[(sample>>7) & 0xFF];
  mantissa = (sample >> (exponent+3)) & 0x0F;
  muLawSample = ~(sign | (exponent << 4) | mantissa);
  /** return the result **/
  return muLawSample;
}

/**
 * Decode a 8-bit mu-Law sample as 16-bit PCM.
 * @param {number} muLawSample The 8-bit mu-Law sample
 * @return {number}
 */
export function decodeSample(muLawSample) {
  /** @type {number} */
  let sign;
  /** @type {number} */
  let exponent;
  /** @type {number} */
  let mantissa;
  /** @type {number} */
  let sample;
  muLawSample = ~muLawSample;
  sign = (muLawSample & 0x80);
  exponent = (muLawSample >> 4) & 0x07;
  mantissa = muLawSample & 0x0F;
  sample = decodeTable[exponent] + (mantissa << (exponent+3));
  if (sign != 0) sample = -sample;
  return sample;
}

/**
 * Encode 16-bit linear PCM samples into 8-bit mu-Law samples.
 * @param {!Int16Array} samples A array of 16-bit PCM samples.
 * @return {!Uint8Array}
 */
export function encode(samples) {
  /** @type {!Uint8Array} */
  let muLawSamples = new Uint8Array(samples.length);
  for (let i=0; i<samples.length; i++) {
    muLawSamples[i] = encodeSample(samples[i]);
  }
  return muLawSamples;
}

/**
 * Decode 8-bit mu-Law samples into 16-bit PCM samples.
 * @param {!Uint8Array} samples A array of 8-bit mu-Law samples.
 * @return {!Int16Array}
 */
export function decode(samples) {
  /** @type {!Int16Array} */
  let pcmSamples = new Int16Array(samples.length);
  for (let i=0; i<samples.length; i++) {
    pcmSamples[i] = decodeSample(samples[i]);
  }
  return pcmSamples;
}