rochars / byte-data

 * Copyright (c) 2017-2018 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 Encode and decode int numbers to and from byte buffers.

 * @see https://github.com/rochars/byte-data

 */

/**

 * A class to write and read integer numbers to and from byte buffers.

 */

export class IntParser {

  /**

   * @param {number} bits The number of bits used by the integer.

   */

  constructor(bits, signed, clamp) {

    /**

     * The number of bits used by one number.

     * @type {number}

     */

    this.bits = bits;

    /**

     * The number of bytes used by one number.

     * @type {number}

     */

    this.bytes = bits < 8 ? 1 : Math.ceil(bits / 8);

    /**

     * @type {number}

     * @protected

     */

    this.max = Math.pow(2, bits) - 1;

    /**

     * @type {number}

     * @protected

     */

    this.min = 0;

    /** @type {number} */

    let r = 8 - ((((bits - 1) | 7) + 1) - bits);

    /**

     * @type {number}

     * @private

     */

    this.lastByteMask_ = Math.pow(2, r > 0 ? r : 8) - 1;

    /**

     * @type {Function}

     * @protected

     */

    this.unpack = this.unpackUnsigned_;

    if (signed) {

      this.max = Math.pow(2, bits) / 2 - 1;

      this.min = -this.max - 1;

      this.unpack = this.unpackSigned_;

    }

    if (clamp) {

      this.overflow_ = this.overflowClamp_;

    }

  }

  /**

   * Write one unsigned integer to a byte buffer.

   * @param {!Uint8Array|!Array<number>} buffer An array of bytes.

   * @param {number} num The number. Overflows are truncated.

   * @param {number=} index The index being written in the byte buffer.

   * @return {number} The next index to write on the byte buffer.

   */

  pack(buffer, num, index=0) {

    if (num !== num || num.constructor != Number) {

      throw new TypeError();

    }

    num = this.overflow_(num);

    buffer[index] = (num < 0 ? num + Math.pow(2, this.bits) : num) & 255;

    index++;

    for (let i = 2, len = this.bytes; i < len; i++) {

      buffer[index] = Math.floor(num / Math.pow(2, ((i - 1) * 8))) & 255;

      index++;

    }

    if (this.bits > 8) {

      buffer[index] = Math.floor(

        num / Math.pow(2, ((this.bytes - 1) * 8))) & this.lastByteMask_;

      index++;

    }

    return index;

  }

  /**

   * Read one unsigned integer from a byte buffer.

   * Does not check for overflows.

   * @param {!Uint8Array|!Array<number>} buffer An array of bytes.

   * @param {number=} index The index to read.

   * @return {number}

   */

  unpack_(buffer, index=0) {

    /** @type {number} */

    let num = 0;

    for(let x = 0; x < this.bytes; x++) {

      num += buffer[index + x] * Math.pow(256, x);

    }

    return num;

  }

  unpackUnsigned_(buffer, index=0) {

    return this.overflow_(this.unpack_(buffer, index));

  }

  /**

   * Read one two's complement signed integer from a byte buffer.

   * @param {!Uint8Array|!Array<number>} buffer An array of bytes.

   * @param {number=} index The index to read.

   * @return {number}

   */

  unpackSigned_(buffer, index=0) {

    return this.overflow_(this.sign_(this.unpack_(buffer, index)));

  }

  /**

   * Truncate values in case of overflow.

   * @param {number} num The number.

   * @private

   */

  overflow_(num) {

    if (num > this.max || num < this.min) {

      throw new RangeError();

    }

    return num;

  }

  /**

   * Truncate values in case of overflow.

   * @param {number} num The number.

   * @private

   */

  /**

   * Sign a number.

   * @param {number} num The number.

   * @return {number}

   * @private

   */

  sign_(num) {

    if (num > this.max) {

      num -= (this.max * 2) + 2;

    }

    return num;

  }

}