[PATCH] Add a topological sort procedure to commit.c

This introduces an in-place topological sort procedure to commit.c.

Given a list of commits, sort_in_topological_order() will perform an in-place
topological sort of that list.

The invariant that applies to the resulting list is:

       a reachable from b => ord(b) < ord(a)

This invariant is weaker than the --merge-order invariant, but is cheaper
to calculate (assuming the list has been identified) and will serve any
purpose where only a minimal topological order guarantee is required.

Signed-off-by: Jon Seymour <jon.seymour@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/commit.h b/commit.h
index 491b2c148f..c24ab21061 100644
--- a/commit.h
+++ b/commit.h
@@ -54,4 +54,17 @@ struct commit *pop_most_recent_commit(struct commit_list **list,
 struct commit *pop_commit(struct commit_list **stack);
 
 int count_parents(struct commit * commit);
+
+/*
+ * Performs an in-place topological sort of list supplied.
+ *
+ * Pre-conditions:
+ *   all commits in input list and all parents of those
+ *   commits must have object.util == NULL
+ *        
+ * Post-conditions: 
+ *   invariant of resulting list is:
+ *      a reachable from b => ord(b) < ord(a)
+ */
+void sort_in_topological_order(struct commit_list ** list);
 #endif /* COMMIT_H */