Maybe I'm crazy, but this doesn't seem to work: 
#!/usr/bin/perl

use strict;
use warnings;

my $mask = hex($ARGV[0]);

my $setbits = unpack("%32b*", $mask);

printf("0x%x has %d set\n", $mask, $setbits);

[download]

Then I run it:
./bittest 0xff
0xff has 11 set

Or worse:
./bittest 0x1001
0x1001 has 14 set

Even the simple case:
./bittest 0
0x0 has 2 set

What is going on here?

In reply to Re^3: Efficient bit counting with a twist. by Anonymous Monk
in thread Efficient bit counting with a twist. by BrowserUk

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