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January 2008

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ECJ Evolutionary Computation Toolkit <[log in to unmask]>
Date:
Mon, 21 Jan 2008 13:41:38 +0000
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ECJ Evolutionary Computation Toolkit <[log in to unmask]>
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Subject:
Re: random seeding
From:
Michael Wilson <[log in to unmask]>
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To: ECJ Evolutionary Computation Toolkit <[log in to unmask]>
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Sean Luke wrote:
> Mersenne Twister has an internal state of 624 longs.  If you fill those 
> longs with a poor-entropy value, or successive poor-entropy values,

Didn't spot this when I first read your email; ec.util.MersenneTwister
has an internal state of 624 /ints/, not 624 longs. FastRNG has the same
amount of internal state (in normal mode, slightly more in secure mode),
but as per the MT19937-64 spec it's organised as 312 64-bit values
instead of 624 32-bit ones.

You may be thinking of old C compilers that defined int as 16 bits and
long as 32 bits. The source for the MersenneTwisterFast class has
several instances of 'a = a&0xffffffff' (where a is an int) with the
comment 'for >32 bit  machines'. Of course this has no effect in Java
because ints are fixed at 32 bits regardless of size.

Michael Wilson
Software Engineer
Purple Frog Text

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