Re: [Qemu-devel] [PATCH 0/7] int128: reparing broken 128 bit memory calculations

[Paolo Bonzini]

On 05/11/2015 17:18, Pierre Morel wrote:
> The size of a memory area can never be negative.
> It follows it must be defined as an unsigned value.
>     
> Let's modify the memory regions size to unsigned 128 integer
> and modify accordingly the 128 bit arithmetic.
>     
> This makes memory size calculations easier and easier to understand.
>     
> I fear loud protest but really, it is a broken concept that
> obfuscate the code.

You are right in fearing loud protest, though the protest is for the
lack of explanation of what is broken.

Since the values are never going to be > 2^65, there is no chance of
overflow.  On the other hand there are cases where we compute
start+size-1, and size-1 *could* overflow if you use unsigned integers.

So I am not sure... why?

Paolo