Are there utility methods for performing unsafe ar

问题:

I'm overriding getting a hash code. There's a point where

Hash = 1210600964 * 31 + -837896230

which causes an OverflowException. Is there a method that I can use, something like:

Hash = addUnsafe(multiplyUnsafe(1210600964, 31), -837896230)

Without needing to link my project to another assembly? I do not want to remove overflow checks. dllimports are OK.

回答1:

You can do the maths with 64-bit numbers instead and then use And to cut off any excess:

Option Infer On
' .....
Shared Function MultiplyWithTruncate(a As Integer, b As Integer) As Integer
    Dim x = CLng(a) * CLng(b)
    Return CInt(x And &HFFFFFFFF)
End Function

Although, as you can mix C# and VB.NET projects in one solution, it might be easiest to write a class in C# to do the unchecked arithmetic, even if you are not keen on adding a reference to another assembly.

It might even be a good idea to write the functions in C# too so that you can test that the VB functions return the expected values. It's what I did to check the above code.

Edit: I was prompted by Joseph Nields' comment to test for performance, and it turned out using CLng instead of Convert.ToInt64 and And works faster.