function kernelCos( x, y ) {
	return addon( x, y );
}
Computes the cosine on \\( \[-\pi/4, \pi/4] \\), where \\( \pi/4 \approx 0.785398164 \\).

@private
@param {number} x - input value (in radians, assumed to be bounded by ~pi/4 in magnitude)
@param {number} y - tail of `x`
@returns {number} cosine

@example
var v = kernelCos( 0.0, 0.0 );
// returns ~1.0

@example
var v = kernelCos( 3.141592653589793/6.0, 0.0 );
// returns ~0.866

@example
var v = kernelCos( 0.785, -1.144e-17 );
// returns ~0.707

@example
var v = kernelCos( NaN, 0.0 );
// returns NaN