Posted by Tim Roberts on 06/23/40 11:57

"geoffp" <fwerfrf@jhgjhfggb.com> wrote:

>I need to generate reproducible random number series.
>
>I've done the obvious - use mt_srand with the same seed. This supposedly
>will create the same series every time.
>
>Is this true? Its not working for me.

Really? I did this:

<?php
mt_srand(1000);
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
echo mt_rand(), "\n";
?>

and it produces the same sequence every time. Note that you can't rely on
the sequence continuing across pages.

>By the way, seeding mt_srand with different integers doesn't necessarily
>produce different series. I've done a little testing and every pair of
>consecutive even and odd numbers produces the same series. eg. seed 0 and 1
>produce the same series, as does 10000 and 10001.

You are correct. The code for mt_srand always sets the bottom bit.
--
- Tim Roberts, timr@probo.com
Providenza & Boekelheide, Inc.

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