Great Circle Associates Firewalls
(February 1994)
 

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Subject: random numbers (was genp.c)
From: Wm Randolph Franklin <wrf @ ecse . rpi . edu>
Date: Thu, 17 Feb 1994 14:35:35 -0500
To: Firewalls @ GreatCircle . COM

Even using a clock could be insufficient on some systems.  I can't
cite Unix examples, but here are some analogous cases that may
suggest possible problems.

1) In the late unlamented Primos's version of 'date', the seconds
would always be a multiple of 4.  I observed this undocumented
'feature' when using the date to create random file names, and got
clashes when I ran a short function twice in rapid succession.

2) The book "One Million Random Digits with 100,000 Normal
Deviates" describes how using a clock to time radioactive decays
did not produce a uniform distribution of the least significant
digit.  Probably the clock was lingering for a slightly different
amount of time on the different digits.

Nevertheless, clock input is certainly better than no clock input.


                                     --------
Wm. Randolph Franklin,  wrf @
 ecse .
 rpi .
 edu, (518) 276-6077;  Fax: -6261
ECSE Dept., 6026 JEC, Rensselaer Polytechnic Inst, Troy NY, 12180 USA


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