[PATCH 1/3] diff_tree_sha1(): avoid rereading trees if possible

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

If the tree has already been read, no need to read it into memory
again.

This also helps when this function is called on temporary trees;
these no longer have to be written to disk.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
---
 tree-diff.c |   33 ++++++++++++++++++++++-----------
 1 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/tree-diff.c b/tree-diff.c
index 9d80dfb..54a6b44 100644
--- a/tree-diff.c
+++ b/tree-diff.c
@@ -195,23 +195,34 @@ int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, stru
 	return 0;
 }
 
+static int get_tree_desc_from_sha1(const unsigned char *sha1,
+		struct tree_desc *t)
+{
+	struct object *o;
+
+	o = lookup_object(sha1);
+	if (o && o->type == OBJ_TREE && o->parsed) {
+		struct tree *tree = (struct tree *)o;
+		t->size = tree->size;
+		t->buf = xmalloc(t->size);
+		memcpy(t->buf, tree->buffer, t->size);
+	} else {
+		t->buf = read_object_with_reference(sha1,
+				tree_type, &t->size, NULL);
+		if (!t->buf)
+			die("unable to read source tree (%s)",
+					sha1_to_hex(sha1));
+	}
+}
+
 int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
 {
-	void *tree1, *tree2;
 	struct tree_desc t1, t2;
 	int retval;
 
-	tree1 = read_object_with_reference(old, tree_type, &t1.size, NULL);
-	if (!tree1)
-		die("unable to read source tree (%s)", sha1_to_hex(old));
-	tree2 = read_object_with_reference(new, tree_type, &t2.size, NULL);
-	if (!tree2)
-		die("unable to read destination tree (%s)", sha1_to_hex(new));
-	t1.buf = tree1;
-	t2.buf = tree2;
+	get_tree_desc_from_sha1(old, &t1);
+	get_tree_desc_from_sha1(new, &t2);
 	retval = diff_tree(&t1, &t2, base, opt);
-	free(tree1);
-	free(tree2);
 	return retval;
 }
 
-- 
1.4.4.2.g0f32-dirty