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############################################################################
#
# File: lcseval.icn
#
# Subject: Procedure to evaluate linear congruence parameters
#
# Author: Ralph E. Griswold
#
# Date: May 23, 1996
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# rcseval(a, c, m) evaluates the constants used in a linear congruence
# recurrence for generating a sequence of pseudo-random numbers.
# a is the multiplicative constant, c is the additive constant, and
# m is the modulus.
#
# Any line of output starting with asterisks indicates a problem.
#
# See Donald E. Knuth, "Random Numbers" in The Art of Computer Programming,
# Vol. 2, Seminumerical Algorithms, Addison-Wesley, Reading, Massachusetts,
# 1969, pp. 1-160.
#
############################################################################
#
# Deficiency: The modulus test for a assumes m is a power of 2.
#
############################################################################
#
# Requires: large integers
#
############################################################################
procedure lcseval(a, c, m)
local b, s
write("a=", a, " (should not have a regular pattern of digits)")
write("c=", c)
write("m=", m, " (should be large)")
if (m / 100) < a < (m - sqrt(m)) then write("a passes range test")
else write("*** a fails range test")
if a % 8 = 5 then write("a passes mod test")
else write("*** a fails mod test")
if (c % 2) ~= 1 then write("c relatively prime to m")
else write("*** c not relatively prime to m")
write("c/m=", c / real(m), " (should be approximately 0.211324865405187)")
b := a - 1
every s := seq() do
if (b ^ s) % m = 0 then stop("potency=", s, " (should be at least 5)")
end
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