############################################################################
#
#	File:     lcseval.icn
#
#	Subject:  Procedure to evaluate linear congruence parameters
#
#	Author:   Ralph E. Griswold
#
#	Date:     May 23, 1996
#
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#
#   This file is in the public domain.
#
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#
#  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.
#
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#
#  Deficiency:  The modulus test for a assumes m is a power of 2.
#
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#
#  Requires:  large integers
#
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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