[Mesa-dev] [GSoC2016] Interested in implementing "Soft" double precision floating point support

Thu Mar 10 14:30:52 UTC 2016

First, thank you all for your answers.

So if I summarize what was said, we need
Ian:
 - add
 - negate
 - absolute value
 - multiply
 - reciprocal
 - convert to single precision
 - convert from single precision
Roland:
 - sqrt
 - comparaison (< / == / >)
 - floor/ceil
I will contact Pat Brown (His name appear in the contact field in [1]) to
know if we need the function below for implement gpu_shader_fp64.
 - pow
 - exp
 - log

About the license

*Like I mentioned in the project description, there are quite a few
existing C implementations of these functions.  Finding one of those that
you can understand and that has a compatible license is probably the best
place to start.*

Main Mesa code is under MIT license.
If I chose to use a GNU GPL license file like Linux kernel [3], my code
must be under GNU GPL and probably all the project too. Am I right?

[1] https://www.opengl.org/registry/specs/ARB/gpu_shader_fp64.txt
[2] http://www.mesa3d.org/license.html
[3]
https://github.com/torvalds/linux/blob/097f70b3c4d84ffccca15195bdfde3a37c0a7c0f/arch/arm/nwfpe/softfloat.c

2016-03-10 2:18 GMT+01:00 Roland Scheidegger <sroland at vmware.com>:

> Am 09.03.2016 um 23:51 schrieb Ian Romanick:
> > On 03/09/2016 02:25 AM, tournier.elie wrote:
> >> Hi everyone.
> >>
> >> My name is Elie TOURNIER, I am enrolled in a French Engineering school
> >> (Telecom Physique Strasbourg) specialized in Medical ICT.
> >> I'm interested in implementing "Soft" double precision floating point
> >> support [1].
> >> Taking this subject seem to be a good way to get my feet wet in the Mesa
> >> code and discover how some of its components works.
> >>
> >> I come to you in order to become know but also to retrieve valuable
> >> information for the success of this project.
> >>
> >> I would like to know more about the following things to understand your
> >> requirements :
> >> 1- "/Each double precision value would be stored in a uvec2/" The IEEE
> >> double precision floating point standard representation requires a 64
> >> bit: 1 for sign, 11 for exponent and the others for fraction [2].
> >> -> How double precision value must be stored?
> >
> > As Emil mentioned, on GLSL 1.30, a uvec2 consists of two, 32-bit
> > unsigned integers.  Each double precision value would be stored in a
> uvec2.
> >
> >> 2- Where can I find |GL_ARB_gpu_shader_fp64 |documentation|?
> >> |
> >>
> >>
> >> This is my first exposure to Mesa. Please excuse me if I am asking basic
> >> questions.
> >
> > For this particular project, you wouldn't need Mesa at all for quite
> > some time.  All of the initial project should be done in "raw" GLSL
> > 1.30, and any OpenGL implementation capable of GLSL 1.30 can be used.
> > You would implement (and test!) a library of functions like 'uvec2
> > addDouble(uvec2 a, uvec2 b)' that would provide all of the required
> > double precision operations.
> >
> > The set of required functions should be pretty small.  I think:
> >
> >  - add
> >  - negate
> >  - absolute value
> >  - multiply
> >  - reciprocal
> >  - convert to single precision
> >  - convert from single precision
> >  - pow (maybe?)
> >  - exp (maybe?)
> >  - log (maybe?)
>
> I don't think you need exp/log. At least glsl dosen't require it, though
> the project isn't clear about it.
> (pow all hw I know of with exactly one exception (that would be intel
> graphics...) implements it as log2/mul/exp2 even for f32 anyway).
> I think though you need sqrt (or rsqrt). And some functions for
> rounding, plus comparison operations. Maybe min/max too (albeit if you
> have comparisons you can emulate them of course).
>
> Roland
>
>
> >
> > I think everything else could be implemented using those functions.
> >
> > Like I mentioned in the project description, there are quite a few
> > existing C implementations of these functions.  Finding one of those
> > that you can understand and that has a compatible license is probably
> > the best place to start.
> >
> >> Please point me to the right resources so that I can better understand
> >> the project. I would also be happy to fix a bug to familiarize myself
> >> with the source code. Any suggestions on bugs that are relevant to the
> >> project will be of great help.
> >>
> >> Regards,
> >> Elie
> >>
> >> [1]
> >>
> http://www.x.org/wiki/SummerOfCodeIdeas/#softdoubleprecisionfloatingpointsupport
> >> [2] http://steve.hollasch.net/cgindex/coding/ieeefloat.html#storage
> >>
> >> PS: If you have any questions, please don't hesitate to contact me.
> >>
> >>
> >> _______________________________________________
> >> mesa-dev mailing list
> >> mesa-dev at lists.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev
> >
> > _______________________________________________
> > mesa-dev mailing list
> > mesa-dev at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/mesa-dev
> >
>
>
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