post-e-voting/source-code/scytl-cryptolib/cryptolib-js-bitwise/lib/index.js

/*
 * Copyright 2018 Scytl Secure Electronic Voting SA
 *
 * All rights reserved
 *
 * See our extended copyright notice in *file 'Copyright.txt' which is part of this source code package
 */
/* jshint node:true */
'use strict';

/**
 * A utility for performing bitwise operations on data.
 */
module.exports = {
  /**
   * Concatenates a list of bytes objects, in the order that they are provided
   * as input.
   *
   * @function concatenate
   * @param {...Uint8Array}
   *            arguments A comma separated list of the bytes objects to
   *            concatenate, in the order that they are provided.
   * @returns {Uint8Array} The concatenation of the bytes objects.
   */
  concatenate: function() {
    var arrays = Array.prototype.slice.call(arguments);

    var totalLength = 0;
    for (var i = 0; i < arrays.length; i++) {
      totalLength += arrays[i].length;
    }

    var concatenated = new Uint8Array(totalLength);
    var offset = 0;
    for (var j = 0; j < arrays.length; j++) {
      concatenated.set(arrays[j], offset);
      offset += arrays[j].length;
    }

    return concatenated;
  },

  /**
   * Slices a subset of bytes from a concatenation of bytes.
   *
   * @function slice
   * @param {Uint8Array}
   *            concatenated The concatenation of bytes.
   * @param {number}
   *            start The index in the concatenation at which to start the
   *            slice (inclusive).
   * @param {number}
   *            [end] The index in the concatenation at which to end the slice
   *            (exclusive). If no end index is supplied then all elements
   *            from the start index to the end of the concatenation will be
   *            sliced.
   * @returns {Uint8Array} The sliced subset of bytes.
   */
  slice: function(concatenated, start, end) {
    var concatenatedArray = Array.apply([], concatenated);
    var slicedArray = concatenatedArray.slice(start, end);

    return new Uint8Array(slicedArray);
  },

  /**
   * Prepends a byte to some existing bytes.
   *
   * @function prepend
   * @param {byte}
   *            byte The byte to prepend.
   * @param {Uint8Array}
   *            bytes The existing bytes.
   * @returns {Uint8Array} The bytes after prepending.
   */
  prepend: function(byte, bytes) {
    var prepended = new Uint8Array(1 + bytes.length);
    prepended.set(new Uint8Array([byte]));
    prepended.set(bytes, 1);

    return prepended;
  },

  /**
   * Appends a byte to some existing bytes.
   *
   * @function append
   * @param {Uint8Array}
   *            bytes The existing bytes.
   * @param {byte}
   *            byte The byte to append.
   * @returns {Uint8Array} The bytes after appending.
   */
  append: function(bytes, byte) {
    var appended = new Uint8Array(bytes.length + 1);
    appended.set(bytes);
    appended.set(new Uint8Array([byte]), bytes.length);

    return appended;
  }
};