[ros-dev] Speed Tests (was: ping Alex regarding log2() for scheduler)

[Ash]

Hello,

I'd like to provide a small VS.NET project file with 5 different tests.

- 46ffffe9 tells everything is alright with the function calculation
- times are measured with QueryPerformanceCounter
- loop run cnt: 0x2ffffff

result orig function            46ffffe9
it took         1491052
result orig function inlined    46ffffe9
it took         1035547
result second proposal inlined  46ffffe9
it took         1244434
result optimized asm            46ffffe9
it took         1338367
result debug asm                46ffffe9
it took         8774815

The second proposal is the original proposal but more shifts - still slower 
tho.

Interesting is the inlined version generated by MSVC, shaving off almost 1/3 
of the overall time.
Also stared as "optimized asm" - no gurantee on register safety tho ;)

For portability and performance sake it should be considered to create a 
compiler macro.
This function is terribly small, any optimisations inside are outweighted by 
the calling overhead in this case.
The most impressive one is the original function inlined, althought the ASM 
would only work on x86.

Please do not think about using 64k tables, thats what, 1/2 of a Sempron L2 
cache?
It would really really trash performance.

Available at: <a href="http://hackersquest.org/kerneltest.html" 
title="Kernel Test Emulator">Kernel Test</a>

<a 
href="http://wohngebaeudeversicherung.einsurance.de/">http://wohngebaeudeversicherung.einsurance.de</a>