Mersenne Twister

The Mersenne Twister is a pseudorandom number generator (PRNG). It is by far the most widely used general-purpose PRNG. Its name derives from the fact that its period length is chosen to be a Mersenne prime.

• C#
• VB.Net
• C
• C++

									Private Const N As UInteger = 624
Private Const M As UInteger = 397
Private Const K As UInteger = &H9908B0DFUI

Private Shared state As UInteger() = New UInteger(N) {}
Private Shared nextRand As UInteger
Private Shared left As Integer = -1

Private Shared Function HighestBit(u As UInteger) As UInteger
	Return ((u) And &H80000000UI)
End Function

Private Shared Function LowestBit(u As UInteger) As UInteger
	Return ((u) And &H1UI)
End Function

Private Shared Function LowestBits(u As UInteger) As UInteger
	Return ((u) And &H7FFFFFFFUI)
End Function

Private Shared Function MixBits(u As UInteger, v As UInteger) As UInteger
	Return (HighestBit(u) Or LowestBits(v))
End Function

Private Shared Function Increment(ByRef u As UInteger) As UInteger
	Dim temp = u
	u += 1
	Return temp
End Function

Private Shared Function Increment(ByRef u As Integer) As Integer
	Dim temp = u
	u += 1
	Return temp
End Function

Private Shared Function Decrement(ByRef u As Integer) As Integer
	u -= 1
	Return u
End Function

Public Shared Sub Seed(_seed As UInteger)
	Dim x As UInteger = (_seed Or 1UI) And &HFFFFFFFFUI
	Dim s As UInteger() = state
	Dim j As Integer
	Dim i As Integer = 0

	left = 0
	s(Increment(i)) = x
	j = CInt(N)

	While Convert.ToBoolean(Decrement(j))
		x = (CLng(x) * 69069UI) And UInteger.MaxValue
		s(Increment(i)) = (x) And &HFFFFFFFFUI
	End While
End Sub

Private Shared Function Reload() As UInteger
	Dim p0 As UInteger = 0
	Dim p2 As UInteger = 2
	Dim pM As UInteger = M
	Dim s0 As UInteger
	Dim s1 As UInteger
	Dim j As Integer

	If left < -1 Then
		Seed(4357UI)
	End If

	left = CInt(N - 1)
	nextRand = state(1)

	s0 = state(0)
	s1 = state(1)
	j = CInt(N - M + 1)
	While Convert.ToBoolean(Decrement(j))
		state(Increment(p0)) = state(Increment(pM)) Xor (MixBits(s0, s1) >> 1) Xor (If(Convert.ToBoolean(LowestBit(s1)), K, 0UI))
		s0 = s1
		s1 = state(Increment(p2))
	End While

	pM = 0
	j = CInt(M)

	While Convert.ToBoolean(Decrement(j))
		state(Increment(p0)) = state(Increment(pM)) Xor (MixBits(s0, s1) >> 1) Xor (If(Convert.ToBoolean(LowestBit(s1)), K, 0UI))
		s0 = s1
		s1 = state(Increment(p2))
	End While

	s1 = state(0)
	state(p0) = state(pM) Xor (MixBits(s0, s1) >> 1) Xor (If(Convert.ToBoolean(LowestBit(s1)), K, 0UI))
	s1 = s1 Xor (s1 >> 11)
	s1 = s1 Xor (s1 << 7) And &H9D2C5680UI
	s1 = s1 Xor (s1 << 15) And &HEFC60000UI

	Return (s1 Xor (s1 >> 18))
End Function

Public Shared Function Random() As UInteger
	Dim y As UInteger

	If Decrement(left) < 0 Then
		Return Reload()
	End If

	y = Increment(nextRand)
	y = y Xor (y >> 11)
	y = y Xor (y << 7) And &H9D2C5680UI
	y = y Xor (y << 15) And &HEFC60000UI

	Return (y Xor (y >> 18))
End Function
								

Example

									Seed(15858)
Dim rand = Random()
								

Output

									3748065792