Add a macro to get the number of elements in a table.

Originally committed as revision 15619 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/common.h

@@ -116,6 +116,7 @@
 #define FFMIN3(a,b,c) FFMIN(FFMIN(a,b),c)
 
 #define FFSWAP(type,a,b) do{type SWAP_tmp= b; b= a; a= SWAP_tmp;}while(0)
+#define FF_ARRAY_ELEMS(a) (sizeof(a) / sizeof((a)[0]))
 
 /* misc math functions */
 extern const uint8_t ff_log2_tab[256];