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in reply to Re^3: How do I make a random shuffle deterministic?
in thread How do I make a random shuffle deterministic?

I just realized you had the same idea. But

1. The sum of two strings can be identical, try "rolf" and "rofl" and "flor"

2. for ( < @array > ) is dangerous nonsense, always do for (  @array  ) without glob

3. if you wanna play save, try a system cmd to get a mac adress.

4. You could determine a unique seed at installation time and store it in a module MyProject::Seed you use later. Like this you have full control (just edit the module) and you only need to fiddle once with the OS for a unique key.

5. you could even request a unique key over web at installation time.

Cheers Rolf

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Re^5: How do I make a random shuffle deterministic?
by Anonymous Monk on Dec 05, 2012 at 17:46 UTC

    Thanks for the tips. It is acceptable if some hosts have the same seed. Still, lessening those occurrences is a good thing. How about this: 

    sub seed {
    my $string = shift;
    my $seed;

    my @ascii = map ord, split //, $string;
    my $product = pop @ascii;
    for ( @ascii ) { $seed += $_ };

    $seed = $seed * $product;

    srand $seed;
}

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      "rolfi" and "flori"?

      just a guess: try multiplying each ord with a different prime (by position) and do a module biggest prime <256 before adding.

      or start a new thread about efficient checksums! :)

      UPDATE: the automatic seeding is quite efficient, so why don't you determine a unique seed at installation time from a random number.

      Cheers Rolf

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Re^5: How do I make a random shuffle deterministic?
by Anonymous Monk on Dec 06, 2012 at 15:07 UTC

    New try after some research. 

    use Sys::Hostname;
use Digest::MD5 qw( md5 );

sub seed {
    my $string = shift;
    my $seed = 0;

    my $digest = md5( $string );
    
    for ( split //, $digest ) {
        $seed = ( $seed * 256 + ord ) % 1e12;
    }

    srand $seed;
}

# main matter
my $hostname = hostname;
seed ( $hostname );

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[d/l]
      Looks fine for me!

      The modules are core and your producing a maximal seed.

      Still think it's exaggerated for your problem...

      ... but it's a good generic solution for similar tasks! =)

      My only concern is readability, better use something like ord $char with an explicit loop var my $char

      Anyway you are still operating on the assumption that hostnames are always different, since I don't know your project this might be ok or not.

      Generating a random seed at installation time would prevent this "problem".

      Cheers Rolf

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