tree_entry(): new tree-walking helper function

This adds a "tree_entry()" function that combines the common operation of
doing a "tree_entry_extract()" + "update_tree_entry()".

It also has a simplified calling convention, designed for simple loops
that traverse over a whole tree: the arguments are pointers to the tree
descriptor and a name_entry structure to fill in, and it returns a boolean
"true" if there was an entry left to be gotten in the tree.

This allows tree traversal with

	struct tree_desc desc;
	struct name_entry entry;

	desc.buf = tree->buffer;
	desc.size = tree->size;
	while (tree_entry(&desc, &entry) {
		... use "entry.{path, sha1, mode, pathlen}" ...
	}

which is not only shorter than writing it out in full, it's hopefully less
error prone too.

[ It's actually a tad faster too - we don't need to recalculate the entry
  pathlength in both extract and update, but need to do it only once.
  Also, some callers can avoid doing a "strlen()" on the result, since
  it's returned as part of the name_entry structure.

  However, by now we're talking just 1% speedup on "git-rev-list --objects
  --all", and we're definitely at the point where tree walking is no
  longer the issue any more. ]

NOTE! Not everybody wants to use this new helper function, since some of
the tree walkers very much on purpose do the descriptor update separately
from the entry extraction. So the "extract + update" sequence still
remains as the core sequence, this is just a simplified interface.

We should probably add a silly two-line inline helper function for
initializing the descriptor from the "struct tree" too, just to cut down
on the noise from that common "desc" initializer.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 31 insertions, 2 deletions

diff --git a/tree-walk.c b/tree-walk.c
index 3922058271..297c6972b9 100644
--- a/tree-walk.c
+++ b/tree-walk.c
@@ -37,7 +37,7 @@ static void entry_extract(struct tree_desc *t, struct name_entry *a)
 
 void update_tree_entry(struct tree_desc *desc)
 {
-	void *buf = desc->buf;
+	const void *buf = desc->buf;
 	unsigned long size = desc->size;
 	int len = strlen(buf) + 1 + 20;
 
@@ -63,7 +63,7 @@ static const char *get_mode(const char *str, unsigned int *modep)
 
 const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
 {
-	void *tree = desc->buf;
+	const void *tree = desc->buf;
 	unsigned long size = desc->size;
 	int len = strlen(tree)+1;
 	const unsigned char *sha1 = tree + len;
@@ -78,6 +78,35 @@ const unsigned char *tree_entry_extract(struct tree_desc *desc, const char **pat
 	return sha1;
 }
 
+int tree_entry(struct tree_desc *desc, struct name_entry *entry)
+{
+	const void *tree = desc->buf, *path;
+	unsigned long len, size = desc->size;
+
+	if (!size)
+		return 0;
+
+	path = get_mode(tree, &entry->mode);
+	if (!path)
+		die("corrupt tree file");
+
+	entry->path = path;
+	len = strlen(path);
+	entry->pathlen = len;
+
+	path += len + 1;
+	entry->sha1 = path;
+
+	path += 20;
+	len = path - tree;
+	if (len > size)
+		die("corrupt tree file");
+
+	desc->buf = path;
+	desc->size = size - len;
+	return 1;
+}
+
 void traverse_trees(int n, struct tree_desc *t, const char *base, traverse_callback_t callback)
 {
 	struct name_entry *entry = xmalloc(n*sizeof(*entry));