rochars / alawmulaw

lib/alaw.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 A-Law codec.
 */

/** @module alawmulaw/alaw */

/** @type {!Array<number>} */
const LOG_TABLE = [
  1,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5, 
  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, 
  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 
];

/**
 * Encode a 16-bit linear PCM sample as 8-bit A-Law.
 * @param {number} sample A 16-bit PCM sample
 * @return {number}
 */
export function encodeSample(sample) {
  /** @type {number} */
  let compandedValue; 
  sample = (sample ==-32768) ? -32767 : sample;
  /** @type {number} */
  let sign = ((~sample) >> 8) & 0x80; 
  if (!sign) {
    sample = sample * -1; 
  }
  if (sample > 32635) {
    sample = 32635; 
  }
  if (sample >= 256)  {
    /** @type {number} */
    let exponent = LOG_TABLE[(sample >> 8) & 0x7F];
    /** @type {number} */
    let mantissa = (sample >> (exponent + 3) ) & 0x0F; 
    compandedValue = ((exponent << 4) | mantissa); 
  } else {
    compandedValue = sample >> 4; 
  } 
  return compandedValue ^ (sign ^ 0x55);
}

/**
 * Decode a 8-bit A-Law sample as 16-bit PCM.
 * @param {number} aLawSample The 8-bit A-Law sample
 * @return {number}
 */
export function decodeSample(aLawSample) {
  /** @type {number} */
  let sign = 0;
  aLawSample ^= 0x55;
  if (aLawSample & 0x80) {

You have used a bitwise operator & in a condition. Did you maybe want to use the logical operator &&

    aLawSample &= ~(1 << 7);
    sign = -1;
  }
  /** @type {number} */
  let position = ((aLawSample & 0xF0) >> 4) + 4;
  /** @type {number} */
  let decoded = 0;
  if (position != 4) {
    decoded = ((1 << position) |
      ((aLawSample & 0x0F) << (position - 4)) |
      (1 << (position - 5)));
  } else {
    decoded = (aLawSample << 1)|1;
  }
  decoded = (sign === 0) ? (decoded) : (-decoded);
  return (decoded * 8) * -1;
}

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

/**
 * Decode 8-bit A-Law samples into 16-bit linear PCM samples.
 * @param {!Uint8Array} samples A array of 8-bit A-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;
}