[Pixman] [PATCH] Do opacity computation with shifts instead of comparing with 0

[Søren Sandmann]

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

Also add a COMPILE_TIME_ASSERT() macro and use it to assert that the
shift is correct.
---
 pixman/pixman-private.h |    3 +++
 pixman/pixman.c         |   14 +++++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/pixman/pixman-private.h b/pixman/pixman-private.h
index 3557fb2..36b9d91 100644
--- a/pixman/pixman-private.h
+++ b/pixman/pixman-private.h
@@ -744,6 +744,9 @@ pixman_region16_copy_from_region32 (pixman_region16_t *dst,
 
 #undef DEBUG
 
+#define COMPILE_TIME_ASSERT(x)						\
+    do { typedef int compile_time_assertion [(x)?1:-1]; } while (0)
+
 /* Turn on debugging depending on what type of release this is
  */
 #if (((PIXMAN_VERSION_MICRO % 2) == 0) && ((PIXMAN_VERSION_MINOR % 2) == 1))
diff --git a/pixman/pixman.c b/pixman/pixman.c
index 47ffdd6..cdf4b75 100644
--- a/pixman/pixman.c
+++ b/pixman/pixman.c
@@ -139,14 +139,18 @@ optimize_operator (pixman_op_t     op,
 		   uint32_t        dst_flags)
 {
     pixman_bool_t is_source_opaque, is_dest_opaque;
-    int opaqueness;
 
-    is_source_opaque = ((src_flags & mask_flags) & FAST_PATH_IS_OPAQUE) != 0;
-    is_dest_opaque = (dst_flags & FAST_PATH_IS_OPAQUE) != 0;
+#define OPAQUE_SHIFT 13
+    
+    COMPILE_TIME_ASSERT (FAST_PATH_IS_OPAQUE == (1 << OPAQUE_SHIFT));
+    
+    is_dest_opaque = (dst_flags & FAST_PATH_IS_OPAQUE);
+    is_source_opaque = ((src_flags & mask_flags) & FAST_PATH_IS_OPAQUE);
 
-    opaqueness = ((is_dest_opaque << 1) | is_source_opaque);
+    is_dest_opaque >>= OPAQUE_SHIFT - 1;
+    is_source_opaque >>= OPAQUE_SHIFT;
 
-    return operator_table[op].opaque_info[opaqueness];
+    return operator_table[op].opaque_info[is_dest_opaque | is_source_opaque];
 }
 
 static void
-- 
1.7.1.1