Pseudo-random numbers/Combined recursive generator MRG32k3a: Difference between revisions

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@@ Line 674: / Line 674: @@
 : 20059
 : 19931</pre>
+=={{header|Nim}}==
+<lang Nim>import algorithm, math, sequtils, strutils, tables
+const
+  # First generator.
+  a1 = [int64 0, 1403580, -810728]
+  m1: int64 = 2^32 - 209
+  # Second generator.
+  a2 = [int64 527612, 0, -1370589]
+  m2: int64 = 2^32 - 22853
+  d = m1 + 1
+type MRG32k3a = object
+  x1: array[3, int64]   # List of three last values of gen #1.
+  x2: array[3, int64]   # List of three last values of gen #2.
+func seed(gen: var MRG32k3a; seedState: int64) =
+  assert seedState in 1..<d
+  gen.x1 = [seedState, 0, 0]
+  gen.x2 = [seedState, 0, 0]
+func nextInt(gen: var MRG32k3a): int64 =
+  let x1i = floormod(a1[0] * gen.x1[0] + a1[1] * gen.x1[1] + a1[2] * gen.x1[2], m1)
+  let x2i = floormod(a2[0] * gen.x2[0] + a2[1] * gen.x2[1] + a2[2] * gen.x2[2], m2)
+  # In version 1.4, the following two lines doesn't work.
+  # gen.x1 = [x1i, gen.x1[0], gen.x1[1]]    # Keep last three.
+  # gen.x2 = [x2i, gen.x2[0], gen.x2[1]]    # Keep last three.
+  gen.x1[2] = gen.x1[1]; gen.x1[1] = gen.x1[0]; gen.x1[0] = x1i
+  gen.x2[2] = gen.x2[1]; gen.x2[1] = gen.x2[0]; gen.x2[0] = x2i
+  result = floormod(x1i - x2i, m1) + 1
+func nextFloat(gen: var MRG32k3a): float =
+  gen.nextInt().float / d.float
+when isMainModule:
+  var gen: MRG32k3a
+  gen.seed(1234567)
+  for _ in 1..5:
+    echo gen.nextInt()
+  echo ""
+  gen.seed(987654321)
+  var counts: CountTable[int]
+  for _ in 1..100_000:
+    counts.inc int(gen.nextFloat() * 5)
+  echo sorted(toSeq(counts.pairs)).mapIt($it[0] & ": " & $it[1]).join(", ")</lang>
+{{out}}
+<pre>1459213977
+3062078038
+2161462912
+4144066119
+2676599027
+: 19871, 1: 20073, 2: 20117, 3: 19867, 4: 20072</pre>
 =={{header|Perl}}==