Author: David Dory
Date: 01:57:20 02/10/02
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On February 10, 2002 at 04:55:19, David Dory wrote: >>David Rasmussen wrote: >>I don't know what Windows you are talking about (and this is also dependant on >>the compiler, actually much more than the OS), but with gcc and MSVC on Windows >>2000, clock() has a pretty high resolution, and is pretty consistent. If I do >>something like the above, I get consistent results. If you're testing the >>difference between to different ways of doing the same thing, and you loop >>enough times, you will get an ok picture of which is faster, and by how much. > >His post showed he was comparing the speed of two functions, using two different >methods of measuring that speed. > >My opinion is that he should compare both functions using ONE measuring method, >rather than using TWO methods. To make the test as valid as possible, all other >variables should be eliminated (in this case, the variable of the second time >measuring method). > >Testing for ONE variable at a time, is the ONLY way to go. > >When you inadvertently add a second variable to the test - well. You can NOW ***** OOPS, dept: ***** ADD THIS: prove or disprove ANYTHING. >> >>But of course I use a profiler for complex problems. After all, clock() isn't >>guaranteed by ANSI C to have a resolution higher than 1 second even. > >MSVC 6 states that clock() has a resolution of 1/1000ths of a second. But you >can't believe that, in my opinion, if the OS is Windows. > >Any Windows OS, (and the older 16-bit'ers are certainly worse), can give you >slightly different times for the exact same task, in my experience, with >clumping. The compiler used is irrelevant. > >For instance, say you time your task at 4.327 seconds. Repeating the exact same >task may give you a sampling of: 4.324, 4.327, 4.330, etc. > >What I haven't seen are results like: 4.326, 4.327, 4.328. > >The results are not perfectly the same, nor are they perfectly granular - >they're "CLUMPY" <grin>, for lack of a better word. > >Sorry, I don't have 7, and know nada about it. > >Dave >> >>BTW. MSVC 7 (which is in beta), doesn't have a profiler. They threw it out from >>MSVC 6, because they believed that it wasn't good enough, and that there were >>many good third party options. But which? Is there a free profiler for MSVC >>available? I use the profiler for gcc sometimes, but since this code is usually >>being compiled with MSVC, a gcc profile isn't exactly precise. >> >>/David
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