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############################################################################
#
# File: random.icn
#
# Subject: Procedures related to random numbers
#
# Authors: Ralph E. Griswold and Gregg M. Townsend
#
# Date: June 24, 2002
#
############################################################################
#
# This file is in the public domain.
#
############################################################################
#
# This file contains procedures related to pseudo-random numbers.
#
# rand_num() is a linear congruential pseudo-random number
# generator. Each time it is called, it produces
# another number in the sequence and also assigns it
# to the global variable random. With no arguments,
# rand_num() produces the same sequence(s) as Icon's
# built-in random-number generator. Arguments can be
# used to get different sequences.
#
# The global variable random serves the same role that
# &random does for Icon's built-in random number
# generator.
#
# rand_int(i) produces a randomly selected integer in the range 1
# to i. It models ?i for positive i.
#
# randomize() sets &random to a "random" value, using /dev/urandom
# if available, otherwise based on the date and time.
#
# randrange(min, max)
# produces random number in the range min <= i <= max.
#
# randrangeseq(i, j)
# generates the integers from i to j in random order.
#
#
# randseq(seed) generates the values of &random, starting at seed,
# that occur as the result of using ?x.
#
# rng(a, c, m, x) generates a sequence of numbers using the linear
# congruence method. With appropriate parameters, the
# result is a pseudo-random sequence. The default
# values produce the sequence used in Icon.
#
# shuffle(x) shuffles the elements of x
#
############################################################################
#
# Links: factors
#
############################################################################
link factors
global random
procedure rand_num(a_, c_, m_) #: random number generator
static random_last, a, c, m
initial {
/random := 0
a := \a_ | 1103515245
c := \c_ | 453816694
m := (\m_ | 2 ^ 31)
}
return random := (a * random + c) % m
end
procedure rand_int(i) #: model ?i
static scale
initial scale := 1.0 / (2 ^ 31 - 1)
(i := (0 < integer(i))) | runerr(205, i)
return integer(i * rand_num() * scale) + 1
end
procedure randomize() #: randomize
local f, s
static ncalls
initial ncalls := 0
ncalls +:= 1
if f := open("/dev/urandom", "ru") then {
s := reads(f, 3)
close(f)
if *\s > 0 then {
&random := ncalls % 113
every &random := 256 * &random + ord(!s)
return
}
}
&random := map("sSmMhH", "Hh:Mm:Ss", &clock) +
map("YyXxMmDd", "YyXx/Mm/Dd", &date) + &time + 1009 * ncalls
return
end
procedure randrange(min, max) #: random number in range
return min - 1 + ?(max - min + 1)
end
procedure randrangeseq(i, j) #: random sequence in range
local x, m, a, c, n
n := j - i + 1
if n < 0 then fail
x := 1
m := nxtprime(n)
a := m + 1
c := nxtprime(m)
every 1 to m do {
x := (a * x + c) % m
if x < n then { # discard out-of-range values
suspend x + i
}
}
end
procedure randseq(seed) #: generate &random
suspend &random := seed
suspend |?1 & &random
end
procedure rng(a, c, m, x) #: random number generator
/a := 1103515245 # multiplicative constant
/c := 453816694 # additive constant
/m := 2 ^ 31 - 1 # modulus
/x := 0 # initial value
suspend x
suspend x := iand(a * |x + c, m)
end
# The procedure shuffle(x) shuffles a string, list, or record.
# In the case that x is a string, a corresponding string with the
# characters randomly rearranged is produced. In the case that x is
# list or records the elements are randomly rearranged.
procedure shuffle(x) #: shuffle
local i
x := string(x) # may fail
every i := *x to 2 by -1 do
x[?i] :=: x[i]
return x
end
# Note: the following procedure is simpler, but does not produce
# as good a shuffle:
#
#procedure shuffle(x)
# x := string(x)
# every !x :=: ?x
# return x
#end
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