function cneg( z ) {
	var v = addon( z );
	return new Complex128( v.re, v.im );
}
Negate a double-precision complex floating-point number.

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

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

var z = new Complex128( -4.2, 5.5 );

var out = cneg( z );
// returns <Complex128>[ 4.2, -5.5 ]

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

var z = new Complex128( 0.0, 0.0 );

var out = cneg( z );
// returns <Complex128>[ -0.0, -0.0 ]

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

var z = new Complex128( NaN, NaN );

var out = cneg( z );
// returns <Complex128>[ NaN, NaN ]