Add AV_HASH_MAX_SIZE.

Makes it easier to use static allocation for the result buffer.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavutil/hash.h

@@ -48,6 +48,18 @@ const char *av_hash_names(int i);
  */
 const char *av_hash_get_name(const struct AVHashContext *ctx);
 
+/**
+ * Maximum value that av_hash_get_size will currently return.
+ *
+ * You can use this if you absolutely want or need to use static allocation
+ * and are fine with not supporting hashes newly added to libavutil without
+ * recompilation.
+ * Note that you still need to check against av_hash_get_size, adding new hashes
+ * with larger sizes will not be considered an ABI change and should not cause
+ * your code to overflow a buffer.
+ */
+#define AV_HASH_MAX_SIZE 32
+
 /**
  * Get the size of the resulting hash value in bytes.
  *