Merge from HEAD: Correct rounding in divide-by-255 code.

2 files changed, 10 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 8610aa486..6db16c35b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2006-02-15  Eric Anholt  <anholt@FreeBSD.org>
+
+	* render/picture.c: (premultiply):
+	Merge from HEAD:
+	Correct rounding in divide-by-255 code.
+
 2006-02-14  Adam Jackson  <ajax@freedesktop.org>
 
 	* include/xorg-config.h.in:
diff --git a/render/picture.c b/render/picture.c
index 3ed60310e..522eb4fa9 100644
--- a/render/picture.c
+++ b/render/picture.c
@@ -860,12 +860,12 @@ static CARD32 xRenderColorToCard32(xRenderColor c)
 static unsigned int premultiply(unsigned int x)
 {
     unsigned int a = x >> 24;
-    unsigned int t = (x & 0xff00ff) * a;
-    t = (t + ((t >> 8) & 0xff00ff) + 0x800080) >> 8;
+    unsigned int t = (x & 0xff00ff) * a + 0x800080;
+    t = (t + ((t >> 8) & 0xff00ff)) >> 8;
     t &= 0xff00ff;
 
-    x = ((x >> 8) & 0xff) * a;
-    x = (x + ((x >> 8) & 0xff) + 0x80);
+    x = ((x >> 8) & 0xff) * a + 0x80;
+    x = (x + ((x >> 8) & 0xff));
     x &= 0xff00;
     x |= t | (a << 24);
     return x;