function trunc2( x ) {
	var sign;
	if (
		isnan( x ) ||
		isInfinite( x ) ||
		x === 0.0
	) {
		return x;
	}
	if ( x < 0 ) {
		x = -x;
		sign = -1.0;
	} else {
		sign = 1.0;
	}
	return sign * pow( 2.0, floor( log2( x ) ) );
}
Rounds a numeric value to the nearest power of two toward zero.

@param {number} x - input value
@returns {number} rounded value

@example
var v = trunc2( 3.141592653589793 );
// returns 2.0

@example
var v = trunc2( 13.0 );
// returns 8.0

@example
var v = trunc2( -0.314 );
// returns -0.25