[PATCH 27/38] pack v4: code to obtain a SHA1 from a sha1ref

[Nicolas Pitre <nico@fluxnic.net>]

Let's start actually parsing pack v4 data.  Here's the first item.

Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
---
 Makefile       |  1 +
 packv4-parse.c | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 packv4-parse.c

diff --git a/Makefile b/Makefile
index 4716113..ba6cafc 100644
--- a/Makefile
+++ b/Makefile
@@ -838,6 +838,7 @@ LIB_OBJS += object.o
 LIB_OBJS += pack-check.o
 LIB_OBJS += pack-revindex.o
 LIB_OBJS += pack-write.o
+LIB_OBJS += packv4-parse.o
 LIB_OBJS += pager.o
 LIB_OBJS += parse-options.o
 LIB_OBJS += parse-options-cb.o
diff --git a/packv4-parse.c b/packv4-parse.c
new file mode 100644
index 0000000..299fc48
--- /dev/null
+++ b/packv4-parse.c
@@ -0,0 +1,30 @@
+/*
+ * Code to parse pack v4 object encoding
+ *
+ * (C) Nicolas Pitre <nico@fluxnic.net>
+ *
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include "cache.h"
+#include "varint.h"
+
+const unsigned char *get_sha1ref(struct packed_git *p,
+				 const unsigned char **bufp)
+{
+	const unsigned char *sha1;
+
+	if (!**bufp) {
+		sha1 = *bufp + 1;
+		*bufp += 21;
+	} else {
+		unsigned int index = decode_varint(bufp);
+		if (index < 1 || index - 1 > p->num_objects)
+			die("bad index in %s", __func__);
+		sha1 = p->sha1_table + (index - 1) * 20;
+	}
+
+	return sha1;
+}
-- 
1.8.4.38.g317e65b