[Mesa-dev] [PATCH 1/6] gallium: document PK2H/UP2H

[Ian Romanick]

On 01/03/2016 10:02 AM, Ilia Mirkin wrote:
> On Sun, Jan 3, 2016 at 12:33 PM, Roland Scheidegger <sroland at vmware.com> wrote:
>> Am 03.01.2016 um 01:37 schrieb Ilia Mirkin:
>>> Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>>> ---
>>>  src/gallium/docs/source/tgsi.rst | 10 ++++++++--
>>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/src/gallium/docs/source/tgsi.rst b/src/gallium/docs/source/tgsi.rst
>>> index 955ece8..f69998f 100644
>>> --- a/src/gallium/docs/source/tgsi.rst
>>> +++ b/src/gallium/docs/source/tgsi.rst
>>> @@ -458,7 +458,9 @@ while DDY is allowed to be the same for the entire 2x2 quad.
>>>
>>>  .. opcode:: PK2H - Pack Two 16-bit Floats
>>>
>>> -  TBD
>>> +.. math::
>>> +
>>> +  dst.x = f32\_to\_f16(src.x) | f32\_to\_f16(src.y) << 16
>> This doesn't quite match the tgsi info description (which says that the
>> result is
>> replicated). If you don't want channel replication probably should make
>> that CHAN
>> there instead.
> 
> I'll add the replication to the docs. Looks like NV_fragment_program
> also wanted this:
> 
>       tmp0 = VectorLoad(op0);
>       /* result obtained by combining raw bits of tmp0.x, tmp0.y */
>       result.x = RawBits(tmp0.x) | (RawBits(tmp0.y) << 16);
>       result.y = RawBits(tmp0.x) | (RawBits(tmp0.y) << 16);
>       result.z = RawBits(tmp0.x) | (RawBits(tmp0.y) << 16);
>       result.w = RawBits(tmp0.x) | (RawBits(tmp0.y) << 16);
> 
> But looks like it's just packing, not actually converting. And it's
> unclear whether UP2H is converting or not... let's assume that they do
> the conversions or else this is going to be useless.

I thought that NV_fragment_program had fp16 as a native type.  You did
something like suffix the instruction with H.  In that case, the pack
instruction wouldn't need to convert.  Right?