Need reviewer: JDK 8 CR for Support Integer overflow

[Eamonn McManus]

On 3 February 2012 00:11, Florian Weimer <fweimer at bfk.de> wrote:
> Would it make sense to replace (x ^ r) < 0 && (x ^ y) >= 0
> with (x ^ y ^ r) < 0?

That would not be correct. For example, it would signal overflow for -1 + 1.

Éamonn


On 3 February 2012 00:11, Florian Weimer <fweimer at bfk.de> wrote:

> * Roger Riggs:
>
> > to support addExact(), subtractExact(), negateExact(), multiplyExact(),
> > and toIntExact() for int and long primitive types.
>
> Would it make sense to replace (x ^ r) < 0 && (x ^ y) >= 0
> in
>
> +    public static int addExact(int x, int y) {
> +        int r = x + y;
> +        if ((x ^ r) < 0 && (x ^ y) >= 0) {
> +            throw new ArithmeticException("Addition overflows an int");
> +        }
> +        return r;
> +    }
>
> with (x ^ y ^ r) < 0?
>
> For substraction, you could use ((x ^ r) & (x ^ y)) < 0.
>
> Will Hotspot be able to optimize away the string construction on the
> exception path in multiplyExact() if the exception is caught locally?
>
> --
> Florian Weimer                <fweimer at bfk.de>
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