diff --git a/libavutil/sha1.c b/libavutil/sha1.c
index 3c46140c72..6ab8c25346 100644
--- a/libavutil/sha1.c
+++ b/libavutil/sha1.c
@@ -118,6 +118,8 @@ void av_sha1_final(AVSHA1* context, uint8_t digest[20]){
     }
 }
 
+// use the following to test
+// gcc -DTEST -DHAVE_AV_CONFIG_H -I.. sha1.c -O3 -W -Wall -o sha1 && time ./sha1
 #ifdef TEST
 #include <stdio.h>
 #undef printf