Messages in this thread | | | Date | Wed, 12 Mar 2003 01:55:38 +0000 | From | Jamie Lokier <> | Subject | Re: Runaway cron task on 2.5.63/4 bk? |
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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
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