[Mesa-dev] [PATCH 09/10] i965/fs: Calculate delta_x and delta_y together.

[Jason Ekstrand]

On Fri, Apr 17, 2015 at 12:02 PM, Matt Turner <mattst88 at gmail.com> wrote:
> On Fri, Apr 17, 2015 at 11:58 AM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>> On Fri, Apr 17, 2015 at 11:56 AM, Matt Turner <mattst88 at gmail.com> wrote:
>>> static inline struct brw_reg
>>> offset(struct brw_reg reg, unsigned delta)
>>> {
>>>    reg.nr += delta;
>>>    return reg;
>>> }
>>>
>>> Presumably you're thinking of offset(fs_reg, unsigned).
>>>
>>> The delta_y variable is only used explicitly on original Gen4 where we
>>> have to use line+mac. The delta values are in consecutive registers
>>> (x0, x1), (y0, y1), and extending it to SIMD16 you add an extra two
>>> registers, giving you (x0, x1), (x2, x3), (y0, y1), (y2, y3). So you
>>> offset 1 register in SIMD8 and two registers in SIMD16.
>>>
>>> Does that warrant a comment?
>>
>> Nope, it's fine.
>
> Okay, but to be clear that wasn't a just rhetorical question. Comments
> are for other people (or the author, once the author has forgotten :)
> so it's sometimes hard to know whether it'll be useful. :)
>
> delta_xy is actually in a different format on original Gen4 than it is
> on other platforms. Other platforms do (x0, x1), (y0, y1), (x2, x3),
> (y2, y3).

You might as well copy and paste some of this e-mail into a comment.
It certainly doesn't hurt.
--Jason