code: function safeAdd_64_4(a, b, c, d)
  	{
  		var lsw, msw, lowOrder, highOrder;
  
  		lsw = (a.lowOrder & 0xFFFF) + (b.lowOrder & 0xFFFF) +
  			(c.lowOrder & 0xFFFF) + (d.lowOrder & 0xFFFF);
  		msw = (a.lowOrder >>> 16) + (b.lowOrder >>> 16) +
  			(c.lowOrder >>> 16) + (d.lowOrder >>> 16) + (lsw >>> 16);
  		lowOrder = ((msw & 0xFFFF) << 16) | (lsw & 0xFFFF);
  
  		lsw = (a.highOrder & 0xFFFF) + (b.highOrder & 0xFFFF) +
  			(c.highOrder & 0xFFFF) + (d.highOrder & 0xFFFF) + (msw >>> 16);
  		msw = (a.highOrder >>> 16) + (b.highOrder >>> 16) +
  			(c.highOrder >>> 16) + (d.highOrder >>> 16) + (lsw >>> 16);
  		highOrder = ((msw & 0xFFFF) << 16) | (lsw & 0xFFFF);
  
  		return new Int_64(highOrder, lowOrder);
  	}
docs: Add four 64-bit integers, wrapping at 2^64. This uses 16-bit operations
  internally to work around bugs in some JS interpreters.
  
  @private
  @param {Int_64} a The first 64-bit integer argument to be added
  @param {Int_64} b The second 64-bit integer argument to be added
  @param {Int_64} c The third 64-bit integer argument to be added
  @param {Int_64} d The fouth 64-bit integer argument to be added
  @return {Int_64} The sum of a + b + c + d