See 'perldoc -f vec' for a faster, better way of handling bitfields. All the rest is bitwise operator magic. 

{
    vec(my $str, 2, 1) = 1;
    vec($str, 5, 1) = 1;
    vec($str, 8, 1) = 1;
    sub mytest {
        my $foo = @_ ? shift : $_; # was 'shift || $_'
        $foo <<= 1;
        $str & $foo == $str;
    }
}

[download]
That code is structured as a closure to keep $str private, but that can be loosened.

Update: Oops, wrong tests. that checks for equality. Here's the real thing, 

{
    vec(my $str, 2, 1) = 1;
    vec($str, 5, 1) = 1;
    vec($str, 8, 1) = 1;
    sub mytest {
        my $foo = @_ ? shift : $_; # was 'shift || $_'
        my $bar = $foo << 1;
        not ($foo & $str) ^ ($bar & $str);
    }
}

[download]
( hope that's right! ;-) The Ancient Philosophy And Programming Languages thread should have said something about Aristotle's formal logic.

Update2: modified mytest's argument handling to behave properly with a numerically false argument.

After Compline,
Zaxo

In reply to Re: fast bit twiddling by Zaxo
in thread fast bit twiddling by spurperl

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