Mersenne twister random number generator

1 files changed, 39 insertions, 0 deletions

diff --git a/lib/pure/mersenne.nim b/lib/pure/mersenne.nim
new file mode 100644
index 000000000..2b12cce73
--- /dev/null
+++ b/lib/pure/mersenne.nim
@@ -0,0 +1,39 @@
+import unsigned
+
+type
+  TMersenneTwister* = object
+    mt: array[0..623, uint32]
+    index: int
+
+proc newMersenneTwister*(seed: int): TMersenneTwister =   
+  result.index = 0
+  result.mt[0]= uint32(seed)
+  for i in 1..623'u32:
+    result.mt[i]= (0x6c078965'u32 * (result.mt[i-1] xor (result.mt[i-1] shr 30'u32)) + i)
+
+proc generateNumbers(m: var TMersenneTwister) =
+  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 TMersenneTwister): int =
+  if m.index == 0:
+    generateNumbers(m)
+  var y = m.mt[m.index]
+  y = y xor (y shr 11'u32)
+  y = y xor ((7'u32 shl y) and 0x9d2c5680'u32)
+  y = y xor ((15'u32 shl y) and 0xefc60000'u32)
+  y = y xor (y shr 18'u32)
+  m.index = (m.index+1) mod 624
+  return int(y)
+
+
+
+# Test
+when isMainModule:
+  var mt = newMersenneTwister(2525)
+
+  for i in 0..99:
+    echo mt.getNum
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