Author: Vincent Diepeveen
Date: 10:49:25 07/05/03
Go up one level in this thread
On July 05, 2003 at 10:58:00, Rafael Andrist wrote:
>On July 05, 2003 at 10:17:38, Omid David Tabibi wrote:
>
>>In Genesis I heavily use the abs() function, and so tried to optimize it.
>>Instead of using the abs() function defined in <math.h>, I wrote the following
>>fucntion:
>>
>>long abs(long x) {
>> long y;
>> y = x >> 31;
>> return (x ^ y) - y;
>>}
>>
>>Testing it using a profiler, I found out that my implementation is about twice
>>slower than the math.h implementation of abs(). I haven't looked at the
>>implementation in math.h, but I can't see how a more optimized version of abs()
>>can be written.
>>
>>Any ideas?
>
>I also tried to optimize the abs() function and found out that the compiler
>already optimized it the right way in most of the cases. The compiler usually
>inlines the abs() function and generates the fastest code. You should look at
>the asm code which may be different from case to case.
>
>If you use abs() to measure (small) distances, you can also try a look-up-table
Assuming that table isn't used much the assembly code is going to run faster of
course.
>regards
>Rafael B. Andrist
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