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

[Ilia Mirkin]

On Mon, Jan 4, 2016 at 8:32 PM, Ian Romanick <idr at freedesktop.org> wrote:
> 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?

Ah that explains why the spec docs don't talk about conversions.
Anyways, we're not going to be adding half-width temp registers to
TGSI until there's a more compelling use-case, until then I think the
current docs that I pushed yesterday can probably stand :)

  -ilia