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As you know, a tiny error log($size) / log(2) could lead to a big error in the result. Perl Differences in the underlying C libraries and hardware can result in those tiny differences on other systems even if they don't exist on your own.

I suppose the error coming from floating point arithmetic can bite me only in the case when $size is a power of 2

You also need to check one less than powers of two for errors rounding up.

249 = 562949953421312

$ perl -E'say int( log(562949953421309) / log(2) )' 48 $ perl -E'say int( log(562949953421310) / log(2) )' 49 XXX $ perl -E'say int( log(562949953421311) / log(2) )' 49 XXX $ perl -E'say int( log(562949953421312) / log(2) )' 49 $ perl -E'say int( log(562949953421313) / log(2) )' 49

(Problem found by accident)


In reply to Re: May I be bitten by floating point arithmetic in the following restricted case? by ikegami
in thread May I be bitten by floating point arithmetic in the following restricted case? by rubasov

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