Add a "rev-tree" helper, which calculates the revision

tree graph.

It's quite fast when the commit-objects are cached, but since
it has to walk every single commit-object, it also allows you
to cache an old state and just add on top of that.

Makefile

@@ -2,7 +2,7 @@ CFLAGS=-g -O3 -Wall
 CC=gcc
 
 PROG=	update-cache show-diff init-db write-tree read-tree commit-tree \
-	cat-file fsck-cache checkout-cache diff-tree
+	cat-file fsck-cache checkout-cache diff-tree rev-tree
 
 all: $(PROG)
 
@@ -40,6 +40,9 @@ checkout-cache: checkout-cache.o read-cache.o
 diff-tree: diff-tree.o read-cache.o
 	$(CC) $(CFLAGS) -o diff-tree diff-tree.o read-cache.o $(LIBS)
 
+rev-tree: rev-tree.o read-cache.o
+	$(CC) $(CFLAGS) -o rev-tree rev-tree.o read-cache.o $(LIBS)
+
 read-cache.o: cache.h
 show-diff.o: cache.h
 

rev-tree.c

@@ -0,0 +1,138 @@
+#include "cache.h"
+
+struct relationship {
+	unsigned char sha1[20];
+	unsigned char parent[20];
+};
+
+static struct relationship **rels;
+static int nr_rels, rel_allocs;
+
+static int find_relationship(unsigned char *sha1, unsigned char *parent)
+{
+	int first = 0, last = nr_rels;
+
+	while (first < last) {
+		int next = (first + last) / 2;
+		struct relationship *rel = rels[next];
+		int cmp;
+
+		cmp = memcmp(sha1, rel->sha1, 20);
+		if (!cmp) {
+			cmp = memcmp(parent, rel->parent, 20);
+			if (!cmp)
+				return next;
+		}
+		if (cmp < 0) {
+			last = next;
+			continue;
+		}
+		first = next+1;
+	}
+	return -first-1;
+}
+
+static int add_relationship(unsigned char *sha1, unsigned char *parent)
+{
+	struct relationship *n;
+	int pos;
+
+	pos = find_relationship(sha1, parent);
+	if (pos >= 0)
+		return 0;
+	pos = -pos-1;
+
+	if (rel_allocs == nr_rels) {
+		rel_allocs = alloc_nr(rel_allocs);
+		rels = realloc(rels, rel_allocs * sizeof(struct relationship *));
+	}
+	n = malloc(sizeof(struct relationship));
+	
+	memmove(rels + pos + 1, rels + pos, (nr_rels - pos) * sizeof(struct relationship *));
+	rels[pos] = n;
+	nr_rels++;
+	memcpy(n->sha1, sha1, 20);
+	memcpy(n->parent, parent, 20);
+	return 1;
+}
+
+static int already_seen(unsigned char *sha1)
+{
+	static char null_sha[20];
+	int pos = find_relationship(sha1, null_sha);
+
+	if (pos < 0) 
+		pos = -pos-1;
+	if (pos < nr_rels && !memcmp(sha1, rels[pos]->sha1, 20))
+		return 1;
+	return 0;
+}
+
+static int parse_commit(unsigned char *sha1)
+{
+	if (!already_seen(sha1)) {
+		void *buffer;
+		unsigned long size;
+		char type[20];
+		unsigned char parent[20];
+
+		buffer = read_sha1_file(sha1, type, &size);
+		if (!buffer || strcmp(type, "commit"))
+			return -1;
+		buffer += 46; /* "tree " + "hex sha1" + "\n" */
+		while (!memcmp(buffer, "parent ", 7) && !get_sha1_hex(buffer+7, parent)) {
+			add_relationship(sha1, parent);
+			parse_commit(parent);
+			buffer += 48;	/* "parent " + "hex sha1" + "\n" */
+		}
+	}
+	return 0;	
+}
+
+static void read_cache_file(const char *path)
+{
+	FILE *file = fopen(path, "r");
+	char line[100];
+
+	while (fgets(line, sizeof(line), file)) {
+		unsigned char sha1[20], parent[20];
+		if (get_sha1_hex(line, sha1) || get_sha1_hex(line + 41, parent))
+			usage("bad rev-tree cache file %s", path);
+		add_relationship(sha1, parent);
+	}
+	fclose(file);
+}
+
+/*
+ * Usage: rev-tree [--cache <cache-file>] <commit-id>
+ *
+ * The cache-file can be quite important for big trees. This is an
+ * expensive operation if you have to walk the whole chain of
+ * parents in a tree with a long revision history.
+ */
+int main(int argc, char **argv)
+{
+	int i;
+	unsigned char sha1[20];
+
+	while (argc > 2) {
+		if (!strcmp(argv[1], "--cache")) {
+			read_cache_file(argv[2]);
+			argv += 2;
+			argc -= 2;
+			continue;
+		}
+		usage("unknown option %s", argv[1]);
+	}
+
+	if (argc != 2 || get_sha1_hex(argv[1], sha1))
+		usage("rev-tree [--cache <cache-file>] <commit-id>");
+	parse_commit(sha1);
+	for (i = 0; i < nr_rels; i++) {
+		char parent[60];
+		struct relationship *rel = rels[i];
+		strcpy(parent, sha1_to_hex(rel->parent));
+		printf("%s %s\n", sha1_to_hex(rel->sha1), parent);
+	}
+	return 0;
+}