Math.round optimization, and round to int

[Remi Forax]

or use 
  r = r * (longBits < 0)? -1: 1;
which should be compiled to a conditional move.

cheers,
Rémi

----- Mail original -----
> De: "Jeff Hain" <jeffhain at rocketmail.com>
> À: core-libs-dev at openjdk.java.net
> Envoyé: Dimanche 5 Juin 2016 20:17:49
> Objet: Math.round optimization, and round to int
> 
> Hi.
> 
> 
> 
> While playing around with Math.round(double) code,
> I found out that
> 
> if (longBits < 0) {
>     r = -r;
> }
> 
> can be replaced with:
> 
> long bitsSignum = (((longBits >> 63) << 1) + 1); // 2*0+1 = 1, or 2*-1+1 = -1
> r *= bitsSignum;
> 
> which seems a bit faster, as one could expect due to less branching.
> 
> 
> 
> NB: The playing was making an "int roundToInt(double)" method.
> I think it would be good to have such a method in Math
> (and also versions for short/byte?),
> because people often use "(int) Math.round(foo)" for this use case,
> which doesn't work when out of int range.
> Moreover, people should rarely catch the bug in their tests,
> since they usually don't test with pathological values.
> 
> Recent example:
> http://alvinalexander.com/java/how-to-round-float-double-to-int-integer-in-java
> 
> 
> 
> -Jeff
> 
>