Author: Daniel Mehrmannn
Date: 12:12:27 03/19/05
Go up one level in this thread
On March 19, 2005 at 09:51:46, Gerd Isenberg wrote:
>On March 19, 2005 at 04:41:26, Thomas Gaksch wrote:
>
>>On March 19, 2005 at 04:22:58, Thomas Gaksch wrote:
>>
>>>sorry, i never used the makefile or an other compiler than vc. i always build
>>>the code with microsoft visual c++ 6.0. with visual c++ 6.0 it works with only
>>>including #include <math.h>
>>>but math.h is only needed for the abs function. you also could write a macro for
>>>the abs function.
>>>thomas
>>
>>sorry, i forgot the example for an abs macro:
>>#define ABS(x) ((x)<0?-(x):(x))
>>
>>bye
>>thomas
>
>Hi Thomas,
>
>with good predictable data pattern the macro, producing a conditional jump is
>fine. Trying to outperform the compiler with arithmetic shift right to force
>branchless code is often worse, ...
>
>long abs(long x) {
> long y;
> y = x >> 31;
> return (x ^ y) - y;
>}
>
>... until compiler is smart enough to produce this x86 code which seems shortest
>and fastest abs() at least for random data. And iirr this is the code of msc6
>abs-intrinsic:
>
> 99 cdq
> 33 C2 xor eax,edx
> 2B C2 sub eax,edx
>
>See http://chessprogramming.org/cccsearch/ccc.php?art_id=304882
>or use CCC-Search-Engine with Subject "Implementation of the abs() function" to
>find further details.
>
>Cheers,
>Gerd
Hi Gerd :)
I tryed the same and my implemtation was allso slower as the MS Vc 6.0 include
:(
Daniel
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