On 03/10/2015 05:05 PM, Jason Ekstrand wrote: > > > On Tue, Mar 10, 2015 at 4:50 PM, Matt Turner <matts...@gmail.com > <mailto:matts...@gmail.com>> wrote: > > On Tue, Mar 10, 2015 at 4:20 PM, Ian Romanick <i...@freedesktop.org > <mailto:i...@freedesktop.org>> wrote: > > On 02/28/2015 12:19 PM, Matt Turner wrote: > >> On Sat, Feb 28, 2015 at 11:47 AM, Thomas Helland > >> <thomashellan...@gmail.com <mailto:thomashellan...@gmail.com>> wrote: > >>> On Feb 28, 2015 8:39 PM, "Jason Ekstrand" <ja...@jlekstrand.net > <mailto:ja...@jlekstrand.net>> wrote: > >>>> > >>>> Both patches are > >>>> > >>>> Reviewed-by: Jason Ekstrand <jason.ekstr...@intel.com > <mailto:jason.ekstr...@intel.com>> > >>> > >>> Could you commit them? > >>> I don't have commit access. > >> > >> I'd like to wait a few days to see if there are any comments about the > >> floating-point optimizations. If not, I'll commit them. (The integer > >> parts are surely fine) > > > > Hmm... does the GLSL spec say anything about integer overflow? For > > large values, (a*b)+(a*c) can produce dramatically different results > > than a*(b+c). > > It says (in 4.1.3 Integers) > > """ > Addition, subtraction, and shift operations resulting in overflow or > underflow will not cause any exception, nor will they saturate, rather > they will “wrap” to yield the low-order 32 bits of the result. > Division and multiplication operations resulting in overflow or > underflow will not cause any exception but will result in an undefined > value. > """ > > More thinking required? > > > Actually.... Assuming that everything's 32-bit, it's 100% ok. A fun and > somewhat surprising fact about modular arithmetic is that it is that > multiplication is still distributive. Yes, it can wrap around, but it > will always wrap around "the same way".
Now that I think about it some more, that does seem obviously true. > --Jason _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
