--- cf.schmorp.de/server/utils/cfhq2xa.C	2016/11/16 23:42:03	1.14
+++ cf.schmorp.de/server/utils/cfhq2xa.C	2016/11/18 05:53:42	1.15
@@ -55,6 +55,13 @@
 # define trV   0x10
 # define trA   0x40
 
+static int32_t
+udiff (uint32_t a, uint32_t b)
+{
+  return a > b ? a - b : b - a;
+
+}
+
 static inline pixel lerp (pixel c1, int w1, pixel c2, int w2, pixel c3, int w3, int shift)
 {
 #if 0
@@ -182,10 +189,10 @@
   pixel YUV1 = RGBAtoYUVA (w1);
   pixel YUV2 = RGBAtoYUVA (w2);
 
-  return ((abs (((YUV1 >> Rshift) & Cmask) - ((YUV2 >> Rshift) & Cmask)) > trY) ||
-          (abs (((YUV1 >> Gshift) & Cmask) - ((YUV2 >> Gshift) & Cmask)) > trU) ||
-          (abs (((YUV1 >> Bshift) & Cmask) - ((YUV2 >> Bshift) & Cmask)) > trV) ||
-          (abs (((YUV1 >> Ashift) & Cmask) - ((YUV2 >> Ashift) & Cmask)) > trA) );
+  return ((udiff ((YUV1 >> Rshift) & Cmask, (YUV2 >> Rshift) & Cmask) > trY) ||
+          (udiff ((YUV1 >> Gshift) & Cmask, (YUV2 >> Gshift) & Cmask) > trU) ||
+          (udiff ((YUV1 >> Bshift) & Cmask, (YUV2 >> Bshift) & Cmask) > trV) ||
+          (udiff ((YUV1 >> Ashift) & Cmask, (YUV2 >> Ashift) & Cmask) > trA) );
 }
 
 static void