lib/elliptic/utils.js

'use strict';

var utils = exports;
var BN = require('bn.js');

utils.assert = function assert(val, msg) {
  if (!val)
    throw new Error(msg || 'Assertion failed');
};

function toArray(msg, enc) {
  if (Array.isArray(msg))
    return msg.slice();
  if (!msg)
    return [];
  var res = [];
  if (typeof msg !== 'string') {
    for (var i = 0; i < msg.length; i++)
      res[i] = msg[i] | 0;
    return res;
  }
  if (!enc) {
    for (var i = 0; i < msg.length; i++) {
      var c = msg.charCodeAt(i);
      var hi = c >> 8;
      var lo = c & 0xff;
      if (hi)
        res.push(hi, lo);
      else
        res.push(lo);
    }
  } else if (enc === 'hex') {
    msg = msg.replace(/[^a-z0-9]+/ig, '');
    if (msg.length % 2 !== 0)
      msg = '0' + msg;
    for (var i = 0; i < msg.length; i += 2)
      res.push(parseInt(msg[i] + msg[i + 1], 16));
  }
  return res;
}
utils.toArray = toArray;

function zero2(word) {
  if (word.length === 1)
    return '0' + word;
  else
    return word;
}
utils.zero2 = zero2;

function toHex(msg) {
  var res = '';
  for (var i = 0; i < msg.length; i++)
    res += zero2(msg[i].toString(16));
  return res;
}
utils.toHex = toHex;

utils.encode = function encode(arr, enc) {
  if (enc === 'hex')
    return toHex(arr);
  else
    return arr;
};

// Represent num in a w-NAF form
function getNAF(num, w) {
  var naf = [];
  var ws = 1 << (w + 1);
  var k = num.clone();
  while (k.cmpn(1) >= 0) {
    var z;
    if (k.isOdd()) {
      var mod = k.andln(ws - 1);
      if (mod > (ws >> 1) - 1)
        z = (ws >> 1) - mod;
      else
        z = mod;
      k.isubn(z);
    } else {
      z = 0;
    }
    naf.push(z);

    // Optimization, shift by word if possible
    var shift = (k.cmpn(0) !== 0 && k.andln(ws - 1) === 0) ? (w + 1) : 1;
    for (var i = 1; i < shift; i++)
      naf.push(0);
    k.iushrn(shift);
  }

  return naf;
}
utils.getNAF = getNAF;

// Represent k1, k2 in a Joint Sparse Form
function getJSF(k1, k2) {
  var jsf = [
    [],
    []
  ];

  k1 = k1.clone();
  k2 = k2.clone();
  var d1 = 0;
  var d2 = 0;
  while (k1.cmpn(-d1) > 0 || k2.cmpn(-d2) > 0) {

    // First phase
    var m14 = (k1.andln(3) + d1) & 3;
    var m24 = (k2.andln(3) + d2) & 3;
    if (m14 === 3)
      m14 = -1;
    if (m24 === 3)
      m24 = -1;
    var u1;
    if ((m14 & 1) === 0) {
      u1 = 0;
    } else {
      var m8 = (k1.andln(7) + d1) & 7;
      if ((m8 === 3 || m8 === 5) && m24 === 2)
        u1 = -m14;
      else
        u1 = m14;
    }
    jsf[0].push(u1);

    var u2;
    if ((m24 & 1) === 0) {
      u2 = 0;
    } else {
      var m8 = (k2.andln(7) + d2) & 7;
      if ((m8 === 3 || m8 === 5) && m14 === 2)
        u2 = -m24;
      else
        u2 = m24;
    }
    jsf[1].push(u2);

    // Second phase
    if (2 * d1 === u1 + 1)
      d1 = 1 - d1;
    if (2 * d2 === u2 + 1)
      d2 = 1 - d2;
    k1.iushrn(1);
    k2.iushrn(1);
  }

  return jsf;
}
utils.getJSF = getJSF;

function cachedProperty(obj, name, computer) {
  var key = '_' + name;
  obj.prototype[name] = function cachedProperty() {
    return this[key] !== undefined ? this[key] :
           this[key] = computer.call(this);
  };
}
utils.cachedProperty = cachedProperty;

function parseBytes(bytes) {
  return typeof bytes === 'string' ? utils.toArray(bytes, 'hex') :
                                     bytes;
}
utils.parseBytes = parseBytes;

function intFromLE(bytes) {
  return new BN(bytes, 'hex', 'le');
}
utils.intFromLE = intFromLE;