Re: [Qemu-devel] Re : Re: [PATCH] sparc32 : Signed integer division overflow

[Richard Henderson <rth@twiddle.net>]

On 03/18/2014 04:43 PM, Olivier DANET wrote:
>>> - x0 = x0 < 0 ? 0x80000000 : 0x7fffffff;
>>> > > + } else if (x1 == -1 && x0 == 0x8000000000000000) {
>>> > > + x0 = 0x7fffffff;
>>> > > overflow = 1;
>> > 
>> > Thanks for the patch! I think based upon Peter's recent series that the 
>> > sign constant would need a ULL suffix in order to function correctly on 
>> > 32-bit platforms.
>> > 
>> > My personal preference would be for (1ULL << 63) unless Peter (CC added) 
>> > can think of a reason to leave the hex constant in its current form?
>> > 
>> > That said, I've tested the patch on a Debian etch Linux image and it 
>> > works for me.
>> > 
> The constant lacks an "ULL" indeed, sorry.
> 
> There are both (1ULL << 63) and 0x8000000000000000[ULL] constants in QEMU code, 
> and not a single 9223372036854775808ULL...
> 
> At least, with (1ULL << 63), we are not tempted to count the zeros.

Not to bike-shed this too much, but INT32_MIN and INT64_MIN would be better and
more descriptive for these.  Honestly, we're supposed to be dealing with signed
numbers here, not the unsigned number you're creating above.


r~