Re: is this a bug of JIT?

From: Jon Skeet [C# MVP] (skeet_at_pobox.com)
Date: 03/06/05 

Date: Sun, 6 Mar 2005 15:35:38 -0000

Nick Malik [Microsoft] <nickmalik@hotmail.nospam.com> wrote:
> Certainly looks like a bug. However, the post also has a misunderstanding
> in it.
>
> You state:
> > int a = 0x79de61c0; //2044617152;
> > a += 0x12345678;
> > //a is 0x8c12b838 //-1944930248
>
> This is incorrect. The result is an integer overflow. The system will do
> one of two things: if it is checked, it will throw an exception. If it is
> unchecked, it will discard the MSB.

The default context in C# is unchecked, in which case the above is
exactly correct. Try it:

using System;

class Test
{
    static void Main(string[] args)
    {
        int a = 0x79de61c0;
        a += 0x12345678;
        Console.WriteLine (a);
    }
}

The result is -1944930248, exactly as stated. The MSB is effectively
not discarded, but remains set and then interpreted as a sign bit. 

-- 
Jon Skeet - <skeet@pobox.com>
http://www.pobox.com/~skeet
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