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From: Paolo Bonzini <pbonzini@redhat.com>
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Date: Mon, 9 Nov 2015 13:20:56 +0100
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Subject: Re: [Qemu-devel] [PATCH 0/7] int128: reparing broken 128 bit memory
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To: Pierre Morel <pmorel@linux.vnet.ibm.com>, qemu-devel <qemu-devel@nongnu.org>



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