rochars / uint-buffer

 * Copyright (c) 2018-2019 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 unsigned integers to and from byte buffers.

 * @see https://github.com/rochars/uint-buffer

 */

/** @module uint-buffer */

/**

 * A class to write and read unsigned ints to and from byte buffers.

 */

export class UintBuffer {

  /**

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

   */

  constructor(bits) {

    /**

     * 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;

  }

  /**

   * Write one unsigned integer to a byte buffer.

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

   * @param {number} num The number.

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

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

   * @throws {TypeError} If num is not a number.

   * @throws {RangeError} On overflow.

   */

  pack(buffer, num, index=0) {

    if (num !== num || typeof num != 'number') {

      throw new TypeError();

    }

    this.overflow(num);

    return this.pack_(buffer, num, index);

  }

  /**

   * Write one unsigned integer to a byte buffer.

   * This method assumes the input has already been validated

   * and should be used only if you know what you are doing.

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

   * @param {number} num The number.

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

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

   */

  /**

   * Read one unsigned integer from a byte buffer.

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

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

   * @return {number} The number.

   * @throws {RangeError} On overflow.

   */

  unpack(buffer, index=0) {

    /** @type {number} */

    let num = this.unpackUnsafe(buffer, index);

    this.overflow(num);

    return num; 

  }

  /**

   * 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}

   */

  unpackUnsafe(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;

  }

  /**

   * Throws range error in case of overflow.

   * @param {number} num The number.

   * @throws {RangeError} On overflow.

   * @protected

   * @ignore

   */

  overflow(num) {

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

      throw new RangeError();

    }

  }

  /**

   * Write one unsigned integer to a byte buffer.

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

   * @param {number} num The number.

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

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

   * @throws {TypeError} If num is not a number.

   * @throws {RangeError} On overflow.

   * @private

   */

  pack_(buffer, num, index=0) {

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

    index++;

    /** @type {number} */

    let len = this.bytes;

    for (let i = 2; 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;

  }

}