function csignum( z ) {
	var re;
	var im;
	var az;

	az = cabs( z );
	if ( az === 0.0 ) {
		return z;
	}
	re = real( z ) / az;
	im = imag( z ) / az;
	return new Complex128( re, im );
}
Evaluates the signum function of a double-precision floating-point complex number.

@param {Complex128} z - complex number
@returns {Complex128} result

@example
var Complex128 = require( '@stdlib/complex/float64/ctor' );
var real = require( '@stdlib/complex/float64/real' );
var imag = require( '@stdlib/complex/float64/imag' );

var v = csignum( new Complex128( -4.2, 5.5 ) );
// returns <Complex128>

var re = real( v );
// returns -0.6069136033622302

var im = imag( v );
// returns 0.79476781392673

v = csignum( new Complex128( 0.0, 0.0 ) );
// returns <Complex128>

re = real( v );
// returns 0.0

im = imag( v );
// returns 0.0

v = csignum( new Complex128( NaN, NaN ) );
// returns <Complex128>

re = real( v );
// returns NaN

im = imag( v );
// returns NaN