diff --git a/libavutil/common.h b/libavutil/common.h
index 6594f7dcbf..6f0f5827e0 100644
--- a/libavutil/common.h
+++ b/libavutil/common.h
@@ -76,6 +76,17 @@
  */
 #define FFNABS(a) ((a) <= 0 ? (a) : (-(a)))
 
+/**
+ * Comparator.
+ * For two numerical expressions x and y, gives 1 if x > y, -1 if x < y, and 0
+ * if x == y. This is useful for instance in a qsort comparator callback.
+ * Furthermore, compilers are able to optimize this to branchless code, and
+ * there is no risk of overflow with signed types.
+ * As with many macros, this evaluates its argument multiple times, it thus
+ * must not have a side-effect.
+ */
+#define FFDIFFSIGN(x,y) (((x)>(y)) - ((x)<(y)))
+
 #define FFMAX(a,b) ((a) > (b) ? (a) : (b))
 #define FFMAX3(a,b,c) FFMAX(FFMAX(a,b),c)
 #define FFMIN(a,b) ((a) > (b) ? (b) : (a))