Re: Runaway cron task on 2.5.63/4 bk?

Jamie Lokier
2003-03-12T01:52:20Z

Andrew Morton wrote:
> > However, gcc is unable to do-the-right-thing and generate 32x32->64
> > multiplies, or 32x64->64 multiplies, even though those are both a _lot_
> > faster than the full 64x64->64 case.
>
> 2.95.3 and 3.2.1 seem to do it right?
>
> long a;
> long b;
> long long c;
>
> void foo(void)
> {
> c = a * b;
> }

Your code is wrong for this test. It does a 32x32->32 multiply, and
then sign extends the result to 64 bits.

The correct test has "c = (long long) a * b;".

-- Jamie