------- Additional Comments From pinskia at physics dot uc dot edu 2005-08-28 23:32 ------- Subject: Re: java.lang.String.equals is suboptimal
On Aug 28, 2005, at 7:25 PM, greenrd at greenrd dot org wrote: > > ------- Additional Comments From greenrd at greenrd dot org > 2005-08-28 23:25 ------- > memcmp (which is compiled for i686 in fedora because it is part of > glibc) is > actually less efficient than the current code on my athlon! I was so > surprised, > I ran the memcmp benchmark again, and the results differed by no more > than +/-2%. > > Here are the wallclock times in ms, followed by the advantage of block > compare > over the current code. n is the length of the strings tested. > > n | Current | block compare | memcmp | Advantage of block compare > ------------------------------------------------------------------- > 10 | 10717 | 9236 | 11957 | 16% > 30 | 16427 | 14618 | 19884 | 12% > 50 | 22181 | 17539 | 27550 | 26% > 70 | 28052 | 20978 | 35243 | 34% > 90 | 32966 | 24695 | 42815 | 33% > 110 | 42975 | 28453 | 55036 | 51% > > All these tests were done on x86 with the same -O, -g and -f flags as > make > bootstrap uses by default, using LD_PRELOAD to "hot-replace" the code, > and > without the assertion enabled in the benchmark. This seems like something glibc's memcmp should be doing also, could you report a bug to glibc about this comparison? Also glibc's memcmp could be improved by doing 128 byte (SSE2 and altivec) comparison at a time so we get a nice speed up there too. -- Pinski -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23495
