1 files changed, 5 insertions, 2 deletions

diff --git a/lib/sha1.h b/lib/sha1.h
index b1db15da1e7..9419750f485 100644
--- a/lib/sha1.h
+++ b/lib/sha1.h
@@ -87,8 +87,11 @@ extern void *sha1_read_ctx (const struct sha1_ctx *ctx, void *resbuf);
 extern void *sha1_buffer (const char *buffer, size_t len, void *resblock);
 
 # endif
-/* Compute SHA1 message digest for bytes read from STREAM.  The
-   resulting message digest number will be written into the 20 bytes
+/* Compute SHA1 message digest for bytes read from STREAM.
+   STREAM is an open file stream.  Regular files are handled more efficiently.
+   The contents of STREAM from its current position to its end will be read.
+   The case that the last operation on STREAM was an 'ungetc' is not supported.
+   The resulting message digest number will be written into the 20 bytes
    beginning at RESBLOCK.  */
 extern int sha1_stream (FILE *stream, void *resblock);