Why does Int32.MaxValue * Int32.MaxValue == 1?

Question

I know, Int32.MaxValue * Int32.MaxValue will yield a number larger than Int32; But, shouldn't this statement raise some kind of an exception?

I ran across this when doing something like IF (X * Y > Z) where all are Int32. X and Y are sufficiently large enough, you get a bogus value from X * Y.

Why is this so and how to get around this? besides casting everything to Int64.

Answer 1

Because int32 confines the results to 32bits.

So, if you have a look at the math at a byte level.

FFFFFFFF * FFFFFFFF = FFFFFFFE00000001

As you can see, the lowest 4 bytes = 1.

Answer 2

By default, C# arithmetic is done in an unchecked context, meaning values will roll over.

You can use the checked and unchecked keywords to control that behavior.