[Mesa-dev] [GSoC] Update about floating point library

[tournier.elie]

Hi everyone,

It's the last week of the GSoC but not the last week of my contribution.
The library of functions isn't finish yet. I still has to debug the
multiply function and to implement the fma.
I wrote a post about my GSoC:
https://hopetech.github.io/tech/2016/08/18/Last_week_GSoC.html

Have a nice day!
Elie

2016-07-29 7:10 GMT+02:00 Connor Abbott <cwabbott0 at gmail.com>:

> (Re-adding the list)
>
> On Mon, Jul 25, 2016 at 4:46 AM, tournier.elie <tournier.elie at gmail.com>
> wrote:
> > Hi.
> >
> > Thanks for your email.
> > It seems that you don't work for nvidia. :P.
> >
> > 1.
> > In my *.shader_test files, I have:
> > [require]
> > GLSL >= 1.30
> >
> > Should I still add "#version 130" at the top of each shaders?
>
> Yes, since AFAIK that's just a requirement on the OpenGL
> implementation ("you must support at least GLSL 1.30 to run this
> test") and it doesn't actually add the version tag. If you take a look
> at any random shader_test file in piglit (e.g.
> tests/spec/glsl-1.30/execution/vs-attrib-ivec4-precision.shader_test)
> you'll see that it declares the version explicitly. And you've already
> seen the kind of shenanigans that happen when you don't add it and
> don't test with Mesa.
>
> >
> > 3.
> > I think that I just need recip and rsqrt to finish the library. (and to
> test
> > my code of course.)
> > I will check which functions does I need to implement
> > GL_ARB_gpu_shader_fp64.
>
> Ok, although I think you'll need to implement fma to get the precision
> you need to implement sqrt, inverse, and rsqrt. I believe "real"
> softfloat libraries use some kind of integer-based higher-precision
> thing, but you don't need an exact result so you don't need to be that
> fancy (again, a good reason why our implementation is probably better
> to base off of!).
>
> Connor
>
> >
> >
> > Elie
> >
> >
> > Le samedi 23 juillet 2016, Connor Abbott <cwabbott0 at gmail.com> a écrit :
> >>
> >> On Sat, Jul 23, 2016 at 3:32 PM, tournier.elie <tournier.elie at gmail.com
> >
> >> wrote:
> >> > Hello,
> >> >
> >> > I hope you are well and that you enjoy these beautiful summer days.
> >> >
> >> > You can found a new post on my blog : https://hopetech.github.io/ .
> >> > During these few days, I implemented eq_fp64, le_fp64, lt_fp64,
> >> > mul_fp64,
> >> > add_fp64 and fp64-to-fp32-conversion. The code can be found on
> >> > https://github.com/Hopetech/libSoftFloat .
> >> >
> >> > Like I say in my post, I will try to make a Docker file for Mesa and
> >> > Piglit
> >> > developers.
> >> > The goal is to have an "easy to install" working environment.
> >> > If you have any ideas/recommandations, please don't hesitate to
> contact
> >> > me.
> >> >
> >> > Have a nice day.
> >> > Elie Tournier
> >> >
> >> > _______________________________________________
> >> > mesa-dev mailing list
> >> > mesa-dev at lists.freedesktop.org
> >> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
> >> >
> >>
> >> Hi,
> >>
> >> Here are a few things to consider:
> >>
> >> 1. If you want your implementation to be pure GLSL 1.30, then you need
> >> to add "#version 130" at the top of all your shaders. Otherwise,
> >> you'll nominally get GLSL 1.10 (which doesn't support bit-twiddling at
> >> all), but certain vendors (*cough* nvidia *cough*) will take it to
> >> mean "just turn all of the extensions on." If you don't add the
> >> version tag, then you might accidentally do something that won't fly
> >> on other implementations. For example, you're using pointers all over
> >> the place in function parameters when that's not valid GLSL 1.30 (or
> >> any other unextended version of GLSL) since GLSL doesn't have the
> >> concept of pointers. Instead, you should be using out/inout parameters
> >> (e.g. "out uint zExpPtr").
> >>
> >> 2. I wouldn't worry too much about underflow, etc. since GLSL doesn't
> >> require it. The goal in the end is to implement fp64 in a way that
> >> satisfies the GLSL spec, so you don't need to worry about implementing
> >> all of IEEE if GLSL says it isn't required.
> >>
> >> 2. For sqrt, rsqrt, mod, and so on, I'd check out Intel's
> >> implementation of them in our compiler:
> >>
> >> https://cgit.freedesktop.org/mesa/mesa/tree/src/compiler/
> nir/nir_lower_double_ops.c
> >> Intel GPU's are missing a lot of the fp64 operations required by GLSL
> >> (they basically only have the ones you already implemented, plus fma),
> >> so we had to emulate the others ourselves. Once you get fma working,
> >> you can just follow the code there to implement the rest, since your
> >> goal is very similar to ours. This should be much more straightforward
> >> than basing your code on another softfloat library, since, like you,
> >> we assume the existence of all the fp32 operations and don't try to be
> >> exact when GLSL doesn't require us to be.
> >>
> >> Connor
>
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