[Spice-devel] [spice-gtk 1/2] Fix possible multimedia time overflow

[Marc-André Lureau]

Hi

----- Original Message -----
> > > > > 
> > > > > 3 - 4294967295 == 4 is not a portable assumption. Neither is
> > > > > (uint32_t) 3 - (uint32_t) 4294967295 == 4
> > > > 
> > > > Ok, I am not an expert in portability, do you have an example where
> > > > this
> > > > would give different results?
> > > > 
> > > 
> > > If int is 64 bit (uint32_t) 3 - (uint32_t) 4294967295 == -4294967292.
> > > It seems weird but is due to the integral promotion rules.
> > 
> > 
> > According to C standard, there is no integer promotion when both operands
> > are
> > of the same type:
> > http://c0x.coding-guidelines.com/6.3.1.8.html:
> >  712 If both operands have the same type, then no further conversion is
> >  needed.
> > 
> 
> You are skipping 710 and 711.

right, but then all platforms we care about use 32bit int afaik, so no promotion occurs. I think we could add a strict check in configure, that would make it clear. Then we don't have to half the max delay. But couldn't we find a more solid solution to handle time warp, by remembering the last time?

> 
> > 
> > > Similar to
> > >    printf("%d\n", (uint16_t) 10 - (uint16_t) 16);
> > > which give -6 (but maybe some people could point out that this result is
> > > not portable either... from my knowledge it is).
> > > 
> 
> This would be a gcc bug then, right ?
> I personally tested with different compilers too. Unless they all are
> not following C rules integer promotion happens.
> 
> > > > > 
> > > > > if time1 == UINT32_MAX and time2 == 3 I expect 4 while if
> > > > > time2 == UINT32_MAX and time2 == 3 (this can happen for different
> > > > > reasons)
> > > > > I expect -4. This make computation easier.
> > > > > 
> > > > > I'll add this example.
> > > > 
> > > > Yeah, some test cases would be useful to understand the problem and the
> > > > solution.
> > > > 
> > > 
> > > Done
> > > 
> > > > Thanks
> > > > 
> > > > > 
> > > > > > ts before the last frame received to check if we overlapped, I
> > > > > > think
> > > > > > (otherwise we should consider this frame as a late frame)
> > > > > > 
> > > > > > 
> > > > > 
> > > 
> 
> Frediano
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