Re: Simple arithmetic?

Inspired by previous answers. As usual, the absence of bugs is totally not guaranteed :) But should be something like that...

use strict;
use warnings;

# greatest common multiple
sub gcm {
    my ( $max, $num ) = @_;

    for ( my $c = 1; ( $num & 1 ) == 0 && $c < 4096; $c <<= 1 ) {
        $num >>= 1;
    }
    my $lcm = 4096 * $num;    # least common multiple

    return int( $max / $lcm ) * $lcm;
}

sub pretty {
    return shift =~ s/\d \K (?= (?: \d{3} )+ \z)/_/xgr;
}

print pretty( gcm( 2_147_483_648, 12 ) ),    "\n";
print pretty( gcm( 3_221_225_472, 5007 ) ),  "\n";
print pretty( gcm( 4_096,         4_096 ) ), "\n";
print pretty( gcm( 8_192,         8_192 ) ), "\n";
print pretty( gcm( 15_000,        8_192 ) ), "\n";
print pretty( gcm( 17_000,        8_192 ) ), "\n";
print pretty( gcm( 17_000,        10 ) ),    "\n";
[download]

output:

2_147_475_456
3_219_861_504
4_096
8_192
8_192
16_384
0
[download]

Comment on Re: Simple arithmetic? Select or Download Code

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Re^2: Simple arithmetic? by BrowserUk (Patriarch) on Mar 08, 2015 at 12:27 UTC
Inspired by previous answers. I like your way of incorporating hdb's powers-of-two observation into the GCD() calculation. the absence of bugs is totally not guaranteed Understood. It's my responsibility to test code I use. It stands up to all the likely scenarios (for my application) that I've tested. Thank you. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I'm with torvalds on this In the absence of evidence, opinion is indistinguishable from prejudice. Agile (and TDD) debunked	[reply]
Re^3: Simple arithmetic? by hdb (Monsignor) on Mar 08, 2015 at 12:47 UTC
Of course, my post came later, so the observation is this Anonymus Monk's own original observation. If in addition, as you comment above, R is prime (different from 2) or only odd, then the LCM is always 4096*R, so the whole discussion redundant...	[reply]
Re^4: Simple arithmetic? by Anonymous Monk on Mar 08, 2015 at 13:03 UTC
Of course, my post came later, so the observation is this Anonymus Monk's own original observation. No, I did mean 'answers' - both of them (the first one doesn't count, of course :) I'm kind of ungood at math - that's the reason for bitshifts, they're more 'visual' :)	[reply]