Here is the VBA code for a class (which I call CVirtTime) that performs random number generation using a "virtual clock" that is not affected by the speed of the computer running the code. This virtual clock will advance the virtual time each time you call method NextRand() which generates uniform random numbers between 0 and 1. You must initialize the instance of the class using either InitMyTime or InitTime. The first method allows you to specify any time and date you want (and therefore you can duplicate the sequence of numbers generated). The method InitTime initializes the class instance using the current system date and time. Using this method you cannot replicate the sequence of random numbers. Once you initialize the class instance the virtual clock "ticks" as fast as the number of calls to method NextRand().
Option Explicit
Private m_nSec As Integer
Private m_nMin As Integer
Private m_nHour As Integer
Private m_nDay As Integer
Private m_nMonth As Integer
Private m_nYear As Integer
Private m_fCounter As Double
Private PI As Double
Private Function Log10(ByVal X As Double) As Double
Log10 = Log(X) / Log(10)
End Function
Private Function AbSin(ByVal X As Double) As Double
AbSin = Abs(Sin(X)) + 1
End Function
Private Function AbCos(ByVal X As Double) As Double
AbCos = Abs(Cos(X)) + 1
End Function
Private Sub INC(ByRef N As Integer)
N = N + 1
End Sub
Public Sub InitMyTime(ByVal nSec As Integer, ByVal nMin As Integer, ByVal nHour As Integer, _
ByVal nDay As Integer, ByVal nMonth As Integer, ByVal nYear As Integer)
m_nSec = Abs(nSec)
If m_nSec > 59 Then m_nSec = 0
m_nHour = Abs(nHour)
If m_nHour > 23 Then m_nHour = 0
m_nMin = Abs(nMin)
If m_nMin > 59 Then m_nHour = 0
m_nDay = Abs(nDay)
If m_nDay > 30 Or m_nDay = 0 Then m_nDay = 1
m_nMonth = Abs(nMonth)
If m_nMonth > 12 Or m_nMonth = 0 Then m_nMonth = 1
m_nYear = Abs(nYear)
If m_nYear < 1900 Then m_nYear = 1900
m_fCounter = 0
PI = 4 * Atn(1)
End Sub
Public Sub InitTime()
Dim t As Date
t = Now
m_nSec = Second(t)
m_nHour = Hour(t)
m_nMin = Minute(t)
m_nDay = Day(t)
m_nMonth = Month(t)
m_nYear = Year(t)
m_fCounter = 0
PI = 4 * Atn(1)
End Sub
Public Function NextRand() As Double
Dim X As Double
' manage the virtual time and date
If m_nSec = 60 Then
m_nSec = 0
INC m_nMin
If m_nMin = 60 Then
m_nMin = 0
INC m_nHour
If m_nHour = 24 Then
m_nHour = 0
INC m_nDay
If m_nDay = 30 Then
m_nDay = 1
INC m_nMonth
If m_nMonth = 12 Then
m_nMonth = 1
INC m_nYear
Else
INC m_nMonth
End If
Else
INC m_nDay
End If
Else
INC m_nHour
End If
Else
INC m_nMin
End If
Else
INC m_nSec
End If
X = (5773 * AbSin(137 * m_nSec) * AbCos(173 * m_nMin) * AbSin(137 * m_nHour)) + _
(2377 * AbSin(237 * m_nDay) * AbCos(117 * m_nMonth) * AbCos(m_nYear))
m_fCounter = m_fCounter + 1
If m_fCounter > 1E+99 Then m_fCounter = 0
X = X + Abs(Sin(m_fCounter) + Log(1 + m_fCounter))
NextRand = X - Int(X)
End Function
Calculating the value for variable X is more of an art than a science (at least in my humble opinion). You can develop so many different kinds of expression to calculate X--some better than others. I tried using the modulo operator in a "creative" way, but found that using sin and cos function works rather well.
Namir
Edited: 15 Feb 2010, 8:52 a.m. after one or more responses were posted
(from the pages cited below.)