[Pixman] [PATCH] Remove broken optimizations in combine_disjoint_over_u()

[Søren Sandmann]

From: Søren Sandmann Pedersen <ssp at redhat.com>

The first broken optimization is that it checks "a != 0x00" where it
should check "s != 0x00". The other is that it skips the computation
when alpha is 0xff. That is wrong because in the formula:

     min (1, (1 - Aa)/Ab)

the render specification states that if Ab is 0, the quotient is
defined to positive infinity. That is the case even if (1 - Aa) is 0.
---
 pixman/pixman-combine.c.template |   14 +++++---------
 test/blitters-test.c             |    2 +-
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/pixman/pixman-combine.c.template b/pixman/pixman-combine.c.template
index c129980..0d3b95d 100644
--- a/pixman/pixman-combine.c.template
+++ b/pixman/pixman-combine.c.template
@@ -1296,17 +1296,13 @@ combine_disjoint_over_u (pixman_implementation_t *imp,
 	comp4_t s = combine_mask (src, mask, i);
 	comp2_t a = s >> A_SHIFT;
 
-	if (a != 0x00)
+	if (s != 0x00)
 	{
-	    if (a != MASK)
-	    {
-		comp4_t d = *(dest + i);
-		a = combine_disjoint_out_part (d >> A_SHIFT, a);
-		UNcx4_MUL_UNc_ADD_UNcx4 (d, a, s);
-		s = d;
-	    }
+	    comp4_t d = *(dest + i);
+	    a = combine_disjoint_out_part (d >> A_SHIFT, a);
+	    UNcx4_MUL_UNc_ADD_UNcx4 (d, a, s);
 
-	    *(dest + i) = s;
+	    *(dest + i) = d;
 	}
     }
 }
diff --git a/test/blitters-test.c b/test/blitters-test.c
index 7ba80eb..77a26dd 100644
--- a/test/blitters-test.c
+++ b/test/blitters-test.c
@@ -465,6 +465,6 @@ main (int argc, const char *argv[])
     }
 
     return fuzzer_test_main("blitters", 2000000,
-			    0x217CF14A,
+			    0x1DB8BDF8,
 			    test_composite, argc, argv);
 }
-- 
1.7.1.1