sha1dc: allow building with the external sha1dc library

Some distros provide SHA1 collision-detect code as a shared library.
It's the same code as we have in git tree (but may be with a different
init default for hash), and git can link with it as well; at least, it
may make maintenance easier, according to our security guys.

This patch allows user to build git linking with the external sha1dc
library instead of the built-in code.  User needs to define
DC_SHA1_EXTERNAL explicitly.  As default without it, the built-in
sha1dc code is used like before.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/sha1dc_git.c b/sha1dc_git.c
index 79466414f8..e0cc9d988c 100644
--- a/sha1dc_git.c
+++ b/sha1dc_git.c
@@ -1,5 +1,16 @@
 #include "cache.h"
 
+#ifdef DC_SHA1_EXTERNAL
+/*
+ * Same as SHA1DCInit, but with default save_hash=0
+ */
+void git_SHA1DCInit(SHA1_CTX *ctx)
+{
+	SHA1DCInit(ctx);
+	SHA1DCSetSafeHash(ctx, 0);
+}
+#endif
+
 /*
  * Same as SHA1DCFinal, but convert collision attack case into a verbose die().
  */