On 30 Apr 2003, Falk Hueffner wrote:
>
> gcc 3.4 will have a __builtin_ctz function which can be used for this.
> It will emit special instructions on CPUs that support it (i386, Alpha
> EV67), and use a lookup table on others, which is very boring, but
> also faster.
Classic mistake. Lookup tables are only faster in benchmarks, they are
almost always slower in real life. You only need to miss in the cache
_once_ on the lookup to lose all the time you won on the previous one
hundred calls.
"Small and simple" is almost always better than the alternatives. I
suspect that's one reason why older versions of gcc often generate code
that actually runs faster than newer versions: the newer versions _look_
like they do a better job, but..
Linus
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This archive was generated by hypermail 2b29 : Wed Apr 30 2003 - 22:00:35 EST