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

[Pierre Morel <pmorel@linux.vnet.ibm.com>]

On 11/09/2015 01:20 PM, Paolo Bonzini wrote:
>
> On 09/11/2015 13:01, Pierre Morel wrote:
>>>> This leads to have UINT64_MAX represented with {1, 0} instead of
>>>> {0, UINT64_MAX} while {1, 0} is 2^64. This again leads to have
>>>> unnecessary and obfuscating transformations with int128_2_64() to
>>>> test for UINT64_MAX and return {1,0} in memory_region_init()
>>>> while using inverse translation test{1,0} and return UINT64_MAX
>>>> in memory_region_size()>>
>>> Yes, the use of UINT64_MAX for 2^64 is a hack, but it is unrelated to
>>> the signedness of Int128.
>> OK, we agree it is a hack,
>> but sorry, I should have missed something,
>> because I do not understand what this hack is useful for.
> It's used in the size argument of memory_region_init*, so that it can
> remain an uint64_t.  The size is usually small (up to 2^40, say) unless
> it is 2^64 meaning "the whole address space".  The latter case is
> covered by UINT64_MAX.
>
> Paolo
>

OK, I understand, thanks for having taking time for me.

To sum-up size is a size :-) and not an offset in memory.

Size of UINT64_MAX does not exist but we can live without it, having
a description for "whole address space", 2^64, can be useful.

Even there may be other solutions like taking 0 for 2^64,
if a memory size of 0 has no meaning,
but it could be misleading too.

So I do not see better solution for this interesting problematic.