in reply to Re^6: &1 is no faster than %2 when checking for oddness. Oh well. (best)
in thread &1 is no faster than %2 when checking for oddness. Oh well.

To make it extremely simple, consider the code:

At last, a technical argument. For safety.

This

sub odd {
    die 'Out of integer range' 
        if $_[ 0 ] & 0xffffffff != $_[ 0 ]; ## Should be done by perl!
    return $_[ 0 ] & 1;
}

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Versus this

sub odd {
    my $num= shift @ARGV;
    die 'Number too big to test for oddness'
        if $num > 9_007_199_254_740__992;

    die 'Number too small to test for oddness' 
        if $num < -9_007_199_254_740__992;

    die 'Cannot test #INFinity for oddness'
        if $num eq '1.#INF';

    die 'Cannot test negative #INFinity for oddness'
        if $num eq '-1.#INF';

    die 'Cannot test #IND for oddness'
        if $num eq '1.#IND';

    die 'Cannot test negative #IND for oddness'
        if $num eq '-1.#IND';

    die 'Cannot test a non number for oddness'
        if $num eq '1.#QNAN;

    die 'Cannot test negative non number for oddness'
        if $num eq '-1.#QNAN;

    die 'Cannot test a non-integer for oddness'  
        if int( $num ) != $num;

    return $num % 2 ? 1 : 0;
}

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Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^8: &1 is no faster than %2 when checking for oddness. Oh well. (odd)
by tye (Sage) on Nov 17, 2006 at 11:59 UTC

    I don't know what I was thinking. Clearly, the simplicity of the error code is the best measure of how useful a subroutine is. So a better oddness tester would surely be: 

    sub odd {
    return 1   if  "1" eq $_[0];
    die "Can't test the oddness of anything but '1'.\n";
}

    [download]

    But then, neither of these are any more complicated than your first one: 

    sub odd {
    my $num= shift @_;
    die "Out of range"   if  2**52 <= abs($num);
    return $num % 2;
}

sub odd {
    my $num= shift @_;
    die "Out of range"   if  1 != (1+$num)-$num;
    return $num % 2;
}

    [download]

    Update: For anyone who cares, I'm done. As is, this is a lot of noise for something pretty trivial and it is going nowhere slow.

    - tye        

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