Add treap implementation

Provide macros to generate a type-specific treap implementation and
various functions to operate on it. It uses obj_pool.h to store memory
nodes in a treap.  Previously committed nodes are never removed from
the pool; after any *_commit operation, it is assumed (correctly, in
the case of svn-fast-export) that someone else must care about them.

Treaps provide a memory-efficient binary search tree structure.
Insertion/deletion/search are about as about as fast in the average
case as red-black trees and the chances of worst-case behavior are
vanishingly small, thanks to (pseudo-)randomness.  The bad worst-case
behavior is a small price to pay, given that treaps are much simpler
to implement.

>From http://www.canonware.com/download/trp/trp_hash/trp.h

[db: Altered to reference nodes by offset from a common base pointer]
[db: Bob Jenkins' hashing implementation dropped for Knuth's]
[db: Methods unnecessary for search and insert dropped]
[rr: Squelched compiler warnings]
[db: Added support for immutable treap nodes]
[jn: Reintroduced treap_nsearch(); with tests]

Signed-off-by: David Barr <david.barr@cordelta.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/test-treap.c b/test-treap.c
new file mode 100644
index 0000000000..cdba5111e1
--- /dev/null
+++ b/test-treap.c
@@ -0,0 +1,65 @@
+/*
+ * test-treap.c: code to exercise the svn importer's treap structure
+ */
+
+#include "cache.h"
+#include "vcs-svn/obj_pool.h"
+#include "vcs-svn/trp.h"
+
+struct int_node {
+	uintmax_t n;
+	struct trp_node children;
+};
+
+obj_pool_gen(node, struct int_node, 3)
+
+static int node_cmp(struct int_node *a, struct int_node *b)
+{
+	return (a->n > b->n) - (a->n < b->n);
+}
+
+trp_gen(static, treap_, struct int_node, children, node, node_cmp)
+
+static void strtonode(struct int_node *item, const char *s)
+{
+	char *end;
+	item->n = strtoumax(s, &end, 10);
+	if (*s == '\0' || (*end != '\n' && *end != '\0'))
+		die("invalid integer: %s", s);
+}
+
+int main(int argc, char *argv[])
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct trp_root root = { ~0 };
+	uint32_t item;
+
+	if (argc != 1)
+		usage("test-treap < ints");
+
+	while (strbuf_getline(&sb, stdin, '\n') != EOF) {
+		item = node_alloc(1);
+		strtonode(node_pointer(item), sb.buf);
+		treap_insert(&root, node_pointer(item));
+	}
+
+	item = node_offset(treap_first(&root));
+	while (~item) {
+		uint32_t next;
+		struct int_node *tmp = node_pointer(node_alloc(1));
+
+		tmp->n = node_pointer(item)->n;
+		next = node_offset(treap_next(&root, node_pointer(item)));
+
+		treap_remove(&root, node_pointer(item));
+		item = node_offset(treap_nsearch(&root, tmp));
+
+		if (item != next && (!~item || node_pointer(item)->n != tmp->n))
+			die("found %"PRIuMAX" in place of %"PRIuMAX"",
+				~item ? node_pointer(item)->n : ~(uintmax_t) 0,
+				~next ? node_pointer(next)->n : ~(uintmax_t) 0);
+		printf("%"PRIuMAX"\n", tmp->n);
+	}
+	node_reset();
+	return 0;
+}