On 18 Jul 2009, at 07:40, joel wrote:
Add me to the bandwagon ;)
How do you handle the fact that sometimes, compiler may otpimize out benchamrk code because it has no side-effects ?
I modified the example to force side-effects by making the variables in the loop global. Consequently it now doesn't get optimised away - compilers sure are clever these days. I have also fixed a couple of minor errors which I spotted when compiling under a different platform, The update may be obtained from: http://tinyurl.com/ksbukc After unpacking the zip file, typical compilation with G++ 4.1 and execution should yield something like: $ g++-4 -DNDEBUG -O4 -o example_timer -I. example_timer.cpp $ ./example_timer Calibrating the clock, for a slow timer this may take a while! Point estimate of clock overhead (t_c): 0.0941176 Potential jitter on t_c (sigma_c) : 9.45022e-14 Increasing precision until I can discriminate between function a and b. The nominal confidence interval (minimum, [median], maximum) represents the region: 1-alpha=0.95 Timing at a nominal precision of 50%: We cannot distinguish between A and B: (-17.2061 [1.58791] 4.79154)% Timing at a nominal precision of 25%: We cannot distinguish between A and B: (0 [0] 0)% Timing at a nominal precision of 12.5%: We cannot distinguish between A and B: (-2.02578 [0.0953992] 1.30765)% Timing at a nominal precision of 6.25%: We cannot distinguish between A and B: (0 [0] 0.471908)% Timing at a nominal precision of 3.125%: We cannot distinguish between A and B: (0 [0.235676] 1.10004)% Timing at a nominal precision of 1.5625%: A is faster than B by: (0.090861 [0.471734] 0.738181)% Regards, -ed