Imports System
Module ExactTwoBits
Sub PrintBits(value As ULong, width As Integer)
Dim s As String = Convert.ToString(CLng(value), 2) ' Convert to binary string
Console.Write(s.PadLeft(width, "0"c)) ' Pad with leading zeros
End Sub
'
' exactBitSet:
' ------------
' Returns True only if:
'
' • pos1 and pos2 are valid (>= 0, < 64, and not equal)
' • value has EXACTLY those two bits set
' • all other bits are OFF
'
' Bit positions are ZERO‑BASED from the RIGHT (LSB = position 0).
'
Function ExactBitSet(pos1 As Integer, pos2 As Integer, value As ULong) As Boolean
If pos1 < 0 OrElse pos2 < 0 OrElse pos1 >= 64 OrElse pos2 >= 64 Then
Return False
End If
If pos1 = pos2 Then
Return False
End If
Dim mask As ULong = (1UL << pos1) Or (1UL << pos2)
Return value = mask
End Function
Structure Test
Public value As ULong
Public x As Integer
Public y As Integer
Public width As Integer
End Structure
Sub Main()
Dim tests() As Test = {
New Test With {.value = &B1000010000UL, .x = 4, .y = 9, .width = 10},
New Test With {.value = &B0010000010UL, .x = 1, .y = 7, .width = 10},
New Test With {.value = &B0000100100UL, .x = 2, .y = 5, .width = 10},
New Test With {.value = &B1000010000UL, .x = 3, .y = 9, .width = 10},
New Test With {.value = &B1001010000UL, .x = 4, .y = 9, .width = 10},
New Test With {.value = &B1111111111UL, .x = 4, .y = 9, .width = 10},
New Test With {.value = &B0000000000UL, .x = 4, .y = 9, .width = 10},
New Test With {.value = &B1000010000UL, .x = 4, .y = 8, .width = 10},
New Test With {.value = 1UL, .x = 0, .y = 0, .width = 1},
New Test With {.value = 1UL, .x = 0, .y = 1, .width = 1},
New Test With {.value = 0UL, .x = 1, .y = 1, .width = 1}
}
For Each t In tests
PrintBits(t.value, t.width)
Console.Write(" bits(" & t.x & ", " & t.y & ") -> ")
Console.WriteLine(If(ExactBitSet(t.x, t.y, t.value), "true", "false"))
Next
End Sub
End Module
'
' OUTPUT:
'
' 1000010000 bits(4, 9) -> true
' 0010000010 bits(1, 7) -> true
' 0000100100 bits(2, 5) -> true
' 1000010000 bits(3, 9) -> false
' 1001010000 bits(4, 9) -> false
' 1111111111 bits(4, 9) -> false
' 0000000000 bits(4, 9) -> false
' 1000010000 bits(4, 8) -> false
' 1 bits(0, 0) -> false
' 1 bits(0, 1) -> false
' 0 bits(1, 1) -> false
'
