[Mesa-dev] [RFC PATCH] mesa: Replace _mesa_round_to_even() with roundeven().

[Matt Turner]

On Wed, Mar 11, 2015 at 3:34 PM, Carl Worth <cworth at cworth.org> wrote:
> So I think I'd like to see at least three or four commits here:
>
>         1. Change _mesa_round_to_even to return a float

I don't think this is really meaningful as a separate change. The
current _mesa_round_to_even function uses IROUND() which rounds to
integer. I could do the conversion back to float in the function
(that's occurring implicitly in
ir_expression::constant_expression_value() already). We'd just be
moving where the (bad) conversion is happening.

Basically, the old thing is broken in multiple ways. Attempting to fix
the individual bugs separately is more work than its worth when the
new implementation is just rintf(x).

>         2. Fix rounding bug in _mesa_round_to_even
>         3. Add unit test for recent rounding-bug fix
>         4. Optimize _mesa_round_to_even with SSE 4.1 ROUND if available

Sure, these seem fine.

I kind of agree that giving the new function the same name as
something from a spec but giving it slightly different behavior might
be bad. Keeping the same name also seems bad though -- changing a
function that takes a float and returns an int to take and return a
double (assuming the float and double implementations are named
_mesa_round_to_evenf and _mesa_round_to_even).

Ken suggested _mesa_roundevenf/_mesa_roundeven. I like this. It says
it's the roundeven function, but doesn't claim that its completely
identical.

> With that: Reviewed-by: Carl Worth <cworth at cworth.org>

I can't really apply a review for a bunch of commits you haven't seen yet. :)

I'll send the three updated/split patches.