code: function(a) {
      var i, v, m = 0xff00;
      for (i = 0; i < a.length; ++i) {
        v = a[i];
        a[i] = (v >>> 24) | ((v >>> 8) & m) | ((v & m) << 8) | (v << 24);
      }
      return a;
    }
docs: byteswap a word array inplace.
  (does not handle partial words)
  @param {sjcl.bitArray} a word array
  @return {sjcl.bitArray} byteswapped array