fp

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+\NeedsTeXFormat{LaTeX2e}
+\ProvidesPackage{fp-random}[1995/02/23]
+
+% Version information
+\def\FP@randomversion{1.0a}
+\message{%
+  `Fixed Point Random,%
+  \space\space\space\space\space\space%
+  \space\space\space\space\space\space\space%
+  Version \FP@randomversion%
+  \space(C) Denis Girou (CNRS/IDRIS)%
+  \space\space\space%
+}
+
+% Resolve dependencies
+\RequirePackage{fp-basic}
+
+% Uniform random value
+
+\newcount\FPseed                % Seed value
+
+\def\FPrandom#1{%
+  % #1 macro, which gets the result
+  %
+  % Uniform random number generator (numbers between 0 and 1)
+  %
+  % Algorithm reproduce from a very old Fortran program (unknown origin!)
+  %
+  %       double precision function RANF()
+  %
+  %       integer SEED
+  %       common /COMSEED/SEED
+  % *
+  %       integer A,M,Q,R
+  %       parameter(A=16807,M=2147483647,Q=127773,R=2836)
+  % *
+  %       integer LO,HI,TEST
+  % *
+  %       HI = SEED/Q
+  %       LO = SEED-HI*Q
+  %       TEST = A*LO-R*HI
+  %       if(TEST.gt.0) then
+  %         SEED = TEST
+  %       else
+  %         SEED = TEST+M
+  %       endif
+  % *
+  %       RANF = DFLOAT(SEED)/DFLOAT(M)
+  % *
+  %       end
+  %
+  %   The macro used a seed value, defined by the counter \FPseed.
+  % If it's unknown at first call, we used an arbitrary value.
+  %
+  %   We verify that we obtain the same results as in Fortran
+  %
+  %   The algorithm seems fairly good. With the Fortran version, we obtain
+  % typically something like 49954 numbers between 0 and 0.5 and 50046 between
+  % 0.5 and 1 for 100000 random numbers, depending of the seed value used.
+  %
+  %   To generate a "pseudo-random" seed, you can consider to use the \time
+  % macro, to intialize the random numbers generator according to the time.
+  %   Something like:
+  % \FPseed=\the\time
+  % \multiply\FPseed\the\day
+  % \multiply\FPseed\the\month
+  % \multiply\FPseed\the\year
+  %
+  %   Of course, it is very slow comparing to "standard" programming
+  % languages. On a RS 6000 370, it's take 51s to generate 100 numbers,
+  % loading time of the test program included (and 0.2s for the Fortran
+  % version ... for 100000 numbers!)
+  %   But you must also notice that Hans van der Meer published in TUGboat
+  % Vol. 15, 1, March 1994, pages 57-58, an article on "Random bit generator
+  % in TeX". In fact, he doesn't give a complete solution to generate uniform
+  % random numbers, but at least give some interesting ideas, and also the
+  % code of a simple but powerful macro \SRtest{choice 1}{choice 2}, which
+  % allow to execute the instructions of "choice 1" or those of "choice 2"
+  % with a probability of 1/2 each. As his method is based on shifts of bits
+  % with almost no computations, it's very fast (around 1000 faster than to do
+  % the same thing that \SRtest with \FPrandom.)
+  %
+  {\FP@beginmessage{RANDOM}%
+   %
+   \ifnum\FPseed=0%
+     \FPseed=123456789%
+     \FP@debug{random: seed value undefined! We will used \the\FPseed.^^J%
+            Define it if you want to generate a different sequence of random%
+	    numbers.}%
+   \else%
+     \FP@debug{random: seed value used: \the\FPseed}%
+   \fi%
+   %
+   \FP@xia=\FPseed%
+   \divide\FP@xia by 127773%
+   \FP@xib=\FP@xia%
+   \multiply\FP@xib by 127773%
+   \advance\FP@xib by -\FPseed%
+   \FP@xib=-\FP@xib%
+   \multiply\FP@xia by 2836%
+   \FPseed=\FP@xib%
+   \multiply\FPseed by 16807%
+   \advance\FPseed by -\FP@xia%
+   %
+   \ifnum\FPseed>0%
+   \else%
+      \advance\FPseed by 2147483647%
+   \fi%
+   \FPdiv\FP@tmpa{\the\FPseed}{2147483647}%
+   \global\let\FP@tmp\FP@tmpa%
+   \global\FPseed=\FPseed%
+   \FP@debug{random: random number: \FP@tmp\space%
+              (new seed value: \the\FPseed)}%
+   %
+   \FP@endmessage{}%
+  }%
+  \let#1\FP@tmp%
+}
+
+\endinput