Well, isn't that just special? I've been writing some tests for
NV_fragment_program_option
before merging the asm-shader-rework-2 branch to Mesa master. While
doing that, I came across a neat case on shipping drivers on real
hardware. These two code sequences produce different results:
ADDC R0, R0, |R0|;
MOV R1 (NE), {1.0};
and
ADD R0, R0, |R0|;
SNE R1, R0, {0.0};
I don't think the absolute-value operator has anything to do with it,
but that's how my test case was written. Gosh... if the ADDC
doesn't set the NE condition code, I'd expect the result in R0 to
be equal to zero. Have I gone completely mad?!?
0.0and{0.0}are different as constants in fragment and vertex programs. The former expands to a vector of{0.0, 0.0, 0.0, 0.0}as you would expect. The later, which is what I used in my program, expands to{0.0, 0.0, 0.0, 1.0}. This follows the same rules as, for example,glVertex3f,glColor3f, etc., so it's not too insane. Ah... the joys of coding in assembly.