Hansi wrote:
I have made today a few tests to compare the different possibilities to search min,max of a value. I had some really strange results which I don't have expected. As environment I use VS2008 Express edition,not managed, defines are SECURE_SCL=0 and NDEBUG=1.
In the comparsion I got the following timings:
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< min_element,max_element:73 minVal=0,maxVal=9999999 min_max: accumulator:2338 minVal=0,maxVal=9999999 min_max: minmax_element:86 minVal=0,maxVal=9999999 min/max handcoded:135 minVal=0,maxVal=9999999 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
For me the strange things are: - that std::min_element and std::max_element is faster as boost::minmax_element - the accumulator library seems in this example really slow
I made some changes to your code. I switched from chrono to boost::timer because that measures CPU time, rather than wall-clock time (at least, I think that's what your chrono-based code was measuring; it seemed more variable). I made it test an array with random contents as well as one with numbers in order. I increased your array size by a factor of 10 to get more stable numbers. Variation attached. With that, on i686 Linux, gcc -O3 I get: sorted array: min_element,max_element:1.89 minVal=0,maxVal=99999999 min_max: accumulator:0.45 minVal=0,maxVal=99999999 min_max: minmax_element:0.48 minVal=0,maxVal=99999999 min/max handcoded:0.79 minVal=0,maxVal=99999999 random array: min_element,max_element:1.8 minVal=7,maxVal=2147483611 min_max: accumulator:0.36 minVal=7,maxVal=2147483611 min_max: minmax_element:0.6 minVal=7,maxVal=2147483611 min/max handcoded:0.71 minVal=7,maxVal=2147483611 And with icc -O3: sorted array: min_element,max_element:0.74 minVal=0,maxVal=99999999 min_max: accumulator:0.51 minVal=0,maxVal=99999999 min_max: minmax_element:0.48 minVal=0,maxVal=99999999 min/max handcoded:0.51 minVal=0,maxVal=99999999 random array: min_element,max_element:0.75 minVal=7,maxVal=2147483611 min_max: accumulator:0.51 minVal=7,maxVal=2147483611 min_max: minmax_element:0.68 minVal=7,maxVal=2147483611 min/max handcoded:0.51 minVal=7,maxVal=2147483611 I'm quite surprised by these numbers, in that: - gcc sometimes beats icc - gcc's accumulator looks significantly faster on random data than sorted data (indeed, on random it's the fastest thing of all). I'd guess that minmax_element is faster on sorted data because branch prediction works better there. Nevertheless, it's clearly very different from your results, in that we have opposite fastest and slowest methods. I suspect you're missing some crucial optimization (probably the inlining of a function somewhere in accumulator). John Bytheway