function gammasgn( x ) {
	var fx;

	if ( isnan( x ) ) {
		return x;
	}
	if ( x > 0 ) {
		return 1.0;
	}
	fx = floor( x );
	if ( x === fx ) {
		return 0.0;
	}
	fx /= 2.0;
	if ( fx === floor( fx ) ) {
		return 1.0;
	}
	return -1.0;
}
Computes the sign of the gamma function.

@param {number} x - input value
@returns {number} sign of the gamma function

@example
var v = gammasgn( 1.0 );
// returns 1.0

v = gammasgn( -2.5 );
// returns -1.0

v = gammasgn( 0.0 );
// returns 0.0

v = gammasgn( NaN );
// returns NaN