Add absolute value
diff --git a/include/util.h b/include/util.h
index 864ddbd..64d8104 100644
--- a/include/util.h
+++ b/include/util.h
@@ -46,7 +46,7 @@
 
 
     /*
-     *  Minimum and maximum
+     *  Minimum, maximum, and absolute value
      */
 
 #undef min
@@ -65,6 +65,13 @@
 	_a > _b ? _a : _b;	\
     } )
 
+#undef abs
+#define abs(x)			\
+    ( {				\
+        typeof(x) _x = (x);	\
+	_x >= 0 ? _x : -_x;	\
+    } )
+
 
     /*
      *  Wait