Here is one way with a more efficient count using the unpack checksum: 
    #!/usr/bin/perl -wl

    use strict;


    my $count = 0;
    my $long;

    open    FILE, "file.txt" or die "Couldn't open file: $!\n";
    binmode FILE;


    while (read FILE, $long, 4) {
        $count += unpack'%32b*', $long;
    }

    print $count;


    __END__

[download]

Or make it more efficient by memoising the calculated values: 

    #!/usr/bin/perl -wl

    use strict;


    my $count = 0;
    my %lookup;
    my $byte;

    open FILE, "file.txt" or die "Couldn't open file: $!\n";
    binmode FILE;


    while (read FILE, $byte, 1) {
        next unless ord $byte;

        if ($lookup{$byte}) {
            $count += $lookup{$byte};
        }
        else {
            $count += $lookup{$byte} = unpack'%8b*', $byte;
        }
    }

    print $count;


    __END__

[download]
But a pure lookup table (as suggested above and previously) would be fastest of all.

--
John.

In reply to Re: counting set bits in binary file by jmcnamara
in thread counting set bits in binary file by dwhite20899

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