On Wednesday, January 21, 2015 01:02:46 PM Matt Turner wrote:
> On Tue, Jan 20, 2015 at 12:11 AM, Kenneth Graunke <kenn...@whitecape.org>
> wrote:
> > On Monday, January 19, 2015 03:31:05 PM Matt Turner wrote:
> >> ---
> >> src/mesa/drivers/dri/i965/brw_eu.c | 22 ++++++++++++++++++++++
> >> src/mesa/drivers/dri/i965/brw_eu.h | 1 +
> >> 2 files changed, 23 insertions(+)
> >>
> >> diff --git a/src/mesa/drivers/dri/i965/brw_eu.c
> >> b/src/mesa/drivers/dri/i965/brw_eu.c
> >> index 9905972..9977eed 100644
> >> --- a/src/mesa/drivers/dri/i965/brw_eu.c
> >> +++ b/src/mesa/drivers/dri/i965/brw_eu.c
> >> @@ -88,6 +88,28 @@ brw_swap_cmod(uint32_t cmod)
> >> }
> >> }
> >>
> >> +/* Returns the corresponding inverted conditional mod. */
> >> +enum brw_conditional_mod
> >> +brw_invert_cmod(enum brw_conditional_mod cmod)
> >> +{
> >> + switch (cmod) {
> >> + case BRW_CONDITIONAL_Z:
> >> + return BRW_CONDITIONAL_NZ;
> >> + case BRW_CONDITIONAL_NZ:
> >> + return BRW_CONDITIONAL_Z;
> >> + case BRW_CONDITIONAL_G:
> >> + return BRW_CONDITIONAL_LE;
> >> + case BRW_CONDITIONAL_GE:
> >> + return BRW_CONDITIONAL_L;
> >> + case BRW_CONDITIONAL_L:
> >> + return BRW_CONDITIONAL_GE;
> >> + case BRW_CONDITIONAL_LE:
> >> + return BRW_CONDITIONAL_G;
> >> + default:
> >> + return BRW_CONDITIONAL_NONE;
> >> + }
> >> +}
> >
> > Heh, I thought this looked familiar...apparently I wrote one too :)
> > http://lists.freedesktop.org/archives/mesa-dev/2014-August/066127.html
> >
> > I wasn't sure whether "invert" meant "flip direction" or "negate condition"
> > until I read the code. How about calling it brw_negate_cmod instead?
> >
> > /* Returns a conditional modifier that negates the condition. */
> > enum brw_conditional_mod
> > brw_negate_cmod(uint32_t cmod)
> > {
> > ...
> > }
> >
> > Either way is fine.
> > Reviewed-by: Kenneth Graunke <kenn...@whitecape.org>
>
> Okay, I changed the name, and in the process of thinking about that
> and a comment Jason made I realized that part of this function was
> wrong. When you negate, you don't want to swap Z <-> NZ. I've changed
> the function accordingly:
>
> + switch (cmod) {
> + case BRW_CONDITIONAL_Z:
> + case BRW_CONDITIONAL_NZ:
> + return cmod;
> [snip]What? This function takes a comparison that produces "A" and gives you a new one that produces "!A". You absolutely have to change == to != (and vice versa), or the function is just plain broken. You had it right the first time. brw_swap_cmod doesn't do that, because it takes `X CMP Y` => A and returns a new comparison such that `Y CMP' X` >= A. In other words, if X < Y, then Y > X. But if X == Y, then Y == X.
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