Inefficiency of `mod'

Jonas Maebe jonas.maebe at elis.ugent.be
Mon Oct 25 11:21:09 CEST 2010


On 25 Oct 2010, at 11:10, Jonas Maebe wrote:

> On 25 Oct 2010, at 10:43, Rugxulo wrote:
>
>> In all
>> seriousness, I would doubt the FPC answer would ever be considered
>> correct in this context (heh, 9 gazillion from "-2 shr 1"? highly
>> unlikely). I'm sure they'll be glad for a test case / bug report.
>
> Yes, that's definitely a compiler bug. Kylix also returns the same  
> results as GPC.

Actually, it's rather strange: "shr" is a logical shift right (both in  
FPC and Borland Pascal, and I assume also in GPC) as opposed to an  
arithmetic shift right. So I guess that Kylix and GPC also perform a  
64 bit logical shift right on the value, but then unlike FPC truncate  
the result back to 32 bits. Otherwise I'm not sure where the "-1"  
comes from when doing "(-2)shr 1".


Jonas





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