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Re (tilly) 1: Power of two round up.

by tilly (Archbishop)
on Dec 15, 2000 at 23:15 UTC ( #46894=note: print w/ replies, xml ) Need Help??


in reply to Power of two round up.

TIMTOWTDI

sub binround { my $out = 1; my $in = shift; while ($in) { $in >>= 1; $out += $out; } $out; }


Comment on Re (tilly) 1: Power of two round up.
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Re: Re (tilly) 1: Power of two round up.
by japhy (Canon) on Dec 15, 2000 at 23:31 UTC
    And an even faster WTDI:
    sub next_pwr { my ($x,$p) = (@_,2); # default to next_pwr(X,2) my $log = log($x)/log($p); $log = int($log+1) if $log != int($log); return $p**$log; }
    You can even add a log() memoization in there:
    { my %LOG = (2 => log(2)); # most common sub next_pwr { my ($x,$p) = (@_,2); # default to next_pwr(X,2) # assertions, etc. die "illegal base: $p" if $p < 2; return 1 if $x == 1; $p = int $p; my $log = ($LOG{$x} ||= log($x)) / ($LOG{$p} ||= log($p)); $log = int($log+1) if $log != int($log); return $p ** $log; } }


    japhy -- Perl and Regex Hacker

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