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#
#
# Nim's Runtime Library
# (c) Copyright 2015 Nim Contributors
# See the file "copying.txt", included in this
# distribution, for details about the copyright.
## The [Mersenne Twister](https://en.wikipedia.org/wiki/Mersenne_Twister)
## random number generator.
## .. note:: The procs in this module work at compile-time.
{.deprecated: "use `std/random` instead".}
runnableExamples:
var rand = newMersenneTwister(uint32.high) ## must be "var"
doAssert rand.getNum() != rand.getNum() ## pseudorandom number
## See also
## ========
## * `random module<random.html>`_ for Nim's standard random number generator
type
MersenneTwister* = object
## The Mersenne Twister.
mt: array[0..623, uint32]
index: int
proc newMersenneTwister*(seed: uint32): MersenneTwister =
## Creates a new `MersenneTwister` with seed `seed`.
result.index = 0
result.mt[0] = seed
for i in 1'u32 .. 623'u32:
result.mt[i] = (0x6c078965'u32 * (result.mt[i-1] xor
(result.mt[i-1] shr 30'u32)) + i)
proc generateNumbers(m: var MersenneTwister) =
for i in 0..623:
var y = (m.mt[i] and 0x80000000'u32) +
(m.mt[(i+1) mod 624] and 0x7fffffff'u32)
m.mt[i] = m.mt[(i+397) mod 624] xor uint32(y shr 1'u32)
if (y mod 2'u32) != 0:
m.mt[i] = m.mt[i] xor 0x9908b0df'u32
proc getNum*(m: var MersenneTwister): uint32 =
## Returns the next pseudorandom `uint32`.
if m.index == 0:
generateNumbers(m)
result = m.mt[m.index]
m.index = (m.index + 1) mod m.mt.len
result = result xor (result shr 11'u32)
result = result xor ((result shl 7'u32) and 0x9d2c5680'u32)
result = result xor ((result shl 15'u32) and 0xefc60000'u32)
result = result xor (result shr 18'u32)
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