|Just another Perl shrine|
Re^4: Efficient bit-twiddling in Perl.by BrowserUk (Pope)
|on Mar 01, 2013 at 12:40 UTC||Need Help??|
Your benchmark is not very realistic. As $n doesn't vary, you are completely ignoring the effect of the CPU cache misses that the lookup table may introduce.
The version of my benchmark I posted was the one I use -- in conjunction with -N=1 and uncommenting the print "@_"; -- to check that the output from all the methods is correct.
For timing runs, I operate on the loop counter $_, which when -N=10e6, is enough to exercise the full range of the table 38 times.
And I still get 20%+ improvement from the AoAs lookup:
In general, I've found it very difficult to detect, much less measure any discernible effect from cpu caching in perl code on my machine. It shows up readily in tight loops in C code, but Perl's memory allocation is so cache unfriendly that it rarely seems to come into play.
I would be interested to see the output from the above on your machine if you have a coupe of minutes.
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