input value
S(x)
var v = fresnels( 0.0 );
// returns 0.0
var v = fresnels( 1.0 );
// returns ~0.438
var v = fresnels( Infinity );
// returns ~0.5
var v = fresnels( -Infinity );
// returns ~-0.5
var v = fresnels( NaN );
// returns NaN
Computes the Fresnel integral S(x).