VBA上的线性同余生成器

Question

我正在尝试在VBA中复制线性同余生成器，但我的程序返回给我一个错误'6'：溢出......

Sub test()
    Dim a As Long, c As Long, period As Long
    Dim seed As Long, sample As Long, max As Long
    Dim i  As Long

    seed = 1234
    sample = 2
    max = 100

    a = 48271
    c = 0
    period = 2 ^ 31 - 1

    For i = 1 To sample
        seed = (a * seed + c) Mod period
    Next i
End Sub

我认为问题出现在for循环的第一个表达式中，详见

a*seed

在循环的第二步。 任何建议解决问题而不分裂

a*seed

in

(100*seed+100*seed+100*seed+...+(a-100*n)*seed

Answer 1

您可以使用变体的decimal subtype并为小数编写自己的mod函数：

Function DecMod(a As Variant, n As Variant) As Variant
    Dim q As Variant
    q = Int(CDec(a) / CDec(n))
    DecMod = a - n * q
End Function

Sub test()
    Dim a As Variant, c As Variant, period As Variant
    Dim seed As Variant, sample As Long, max As Long
    Dim i  As Long

    seed = CDec(1234)
    sample = 5
    max = 100

    a = CDec(48271)
    c = 0
    period = CDec(2 ^ 31 - 1)

    For i = 1 To sample
        Debug.Print seed
        seed = DecMod(seed * a + c, period)
    Next i
End Sub

输出：

1234 
59566414 
1997250508 
148423250 
533254358