Imports System
Module CopyBitsModule
'
' Handles edge cases:
' - Validates i and j
' - Prevents undefined behavior from shifting by ≥ 64 bits
' - Masks M so only the required bits are copied
'
' Convert unsigned 64‑bit integer to binary string without leading zeros
Function ToBinary(x As ULong) As String
If x = 0UL Then
Return "0"
End If
Dim s As String = ""
While x <> 0UL
If (x And 1UL) = 1UL Then
s = "1" & s
Else
s = "0" & s
End If
x >>= 1
End While
Return s
End Function
' Copy bits from M into N between bit positions [i, j]
Function CopyBits(N As ULong, M As ULong, i As Integer, j As Integer) As ULong
If i < 0 OrElse j < 0 OrElse i > j OrElse j >= 63 Then
Throw New ArgumentException("Invalid bit range")
End If
Dim length As Integer = j - i + 1
' Mask for bits i..j
Dim mask As ULong = ((1UL << length) - 1UL) << i
' Clear bits i..j in N
Dim N_cleared As ULong = N And Not mask
' Take only the needed bits from M and shift into place
Dim M_shifted As ULong = (M And ((1UL << length) - 1UL)) << i
Return N_cleared Or M_shifted
End Function
Sub Main()
'
' N: 100 011111 00
' M: 110011
' Result: 100 110011 00
'
Dim N As ULong = &B10001111100UL
Dim M As ULong = &B110011UL
Dim result As ULong = CopyBits(N, M, 2, 7)
Console.WriteLine("N: " & ToBinary(N))
Console.WriteLine("M: " & ToBinary(M))
Console.WriteLine("Result: " & ToBinary(result))
End Sub
End Module
'
' OUTPUT:
'
' N: 10001111100
' M: 110011
' Result: 10011001100
'
