[AD] set_difference_blender patch

[Jon Rafkind <workmin@xxxxxxxxxx>]

Anyone mind if I apply this patch to set_difference_blender for 4.4? It
clamps the lowest value to 0 instead of using ABS to wrap around. Heres
a post on a.cc that no one responded to:
http://www.allegro.cc/forums/thread/606235

I can add an example program if someone wants.

Index: colblend.c
===================================================================
--- colblend.c	(revision 14428)
+++ colblend.c	(working copy)
@@ -209,9 +209,9 @@
  */
 unsigned long _blender_difference24(unsigned long x, unsigned long y, unsigned long n)
 {
-   return BLEND(24, ABS(getr24(y) - getr24(x)),
-		    ABS(getg24(y) - getg24(x)),
-		    ABS(getb24(y) - getb24(x)));
+   return BLEND(24, MAX(getr24(y) - getr24(x), 0),
+		    MAX(getg24(y) - getg24(x), 0),
+		    MAX(getb24(y) - getb24(x), 0));
 }
 
 
@@ -496,9 +496,9 @@
  */
 unsigned long _blender_difference16(unsigned long x, unsigned long y, unsigned long n)
 {
-   return BLEND(16, ABS(getr16(y) - getr16(x)),
-		    ABS(getg16(y) - getg16(x)),
-		    ABS(getb16(y) - getb16(x)));
+   return BLEND(16, MAX(getr16(y) - getr16(x), 0),
+		    MAX(getg16(y) - getg16(x), 0),
+		    MAX(getb16(y) - getb16(x), 0));
 }
 
 
@@ -776,9 +776,9 @@
  */
 unsigned long _blender_difference15(unsigned long x, unsigned long y, unsigned long n)
 {
-   return BLEND(15, ABS(getr15(y) - getr15(x)),
-		    ABS(getg15(y) - getg15(x)),
-		    ABS(getb15(y) - getb15(x)));
+   return BLEND(15, MAX(getr15(y) - getr15(x), 0),
+		    MAX(getg15(y) - getg15(x), 0),
+		    MAX(getb15(y) - getb15(x), 0));
 }