function sum( arr ) {
	var len;
	var s;
	var i;
	len = arr.length;
	s = 0;
	for ( i = 0; i < len; i++ ) {
		s += arr[ i ];
	}
	return s;
}
Computes the sum of elements in an array.

@private
@param {Array} arr - input array
@returns {number} sum