commit: add generation number to struct commit

derrickstolee · gitster · commit 83073cc994cc · 2018-05-22T12:36:25.000+09:00
The generation number of a commit is defined recursively as follows:

* If a commit A has no parents, then the generation number of A is one.
* If a commit A has parents, then the generation number of A is one
  more than the maximum generation number among the parents of A.

Add a uint32_t generation field to struct commit so we can pass this
information to revision walks. We use three special values to signal
the generation number is invalid:

GENERATION_NUMBER_INFINITY 0xFFFFFFFF
GENERATION_NUMBER_MAX 0x3FFFFFFF
GENERATION_NUMBER_ZERO 0

The first (_INFINITY) means the generation number has not been loaded or
computed. The second (_MAX) means the generation number is too large to
store in the commit-graph file. The third (_ZERO) means the generation
number was loaded from a commit graph file that was written by a version
of git that did not support generation numbers.

Signed-off-by: Derrick Stolee &lt;dstolee@microsoft.com&gt;
Signed-off-by: Junio C Hamano &lt;gitster@pobox.com&gt;
diff --git a/alloc.c b/alloc.c
@@ -94,6 +94,7 @@ void *alloc_commit_node(void)
 	c->object.type = OBJ_COMMIT;
 	c->index = alloc_commit_index();
 	c->graph_pos = COMMIT_NOT_FROM_GRAPH;
+	c->generation = GENERATION_NUMBER_INFINITY;
 	return c;
 }
 
diff --git a/commit-graph.c b/commit-graph.c
@@ -262,6 +262,8 @@ static int fill_commit_in_graph(struct commit *item, struct commit_graph *g, uin
 	date_low = get_be32(commit_data + g->hash_len + 12);
 	item->date = (timestamp_t)((date_high << 32) | date_low);
 
+	item->generation = get_be32(commit_data + g->hash_len + 8) >> 2;
+
 	pptr = &item->parents;
 
 	edge_value = get_be32(commit_data + g->hash_len);
diff --git a/commit.h b/commit.h
@@ -10,6 +10,9 @@
 #include "pretty.h"
 
 #define COMMIT_NOT_FROM_GRAPH 0xFFFFFFFF
+#define GENERATION_NUMBER_INFINITY 0xFFFFFFFF
+#define GENERATION_NUMBER_MAX 0x3FFFFFFF
+#define GENERATION_NUMBER_ZERO 0
 
 struct commit_list {
 	struct commit *item;
@@ -30,6 +33,7 @@ struct commit {
 	 */
 	struct tree *maybe_tree;
 	uint32_t graph_pos;
+	uint32_t generation;
 };
 
 extern int save_commit_buffer;

Original file line number	Diff line number	Diff line change
`@@ -94,6 +94,7 @@ void *alloc_commit_node(void)`
`94`	`94`	`c->object.type = OBJ_COMMIT;`
`95`	`95`	`c->index = alloc_commit_index();`
`96`	`96`	`c->graph_pos = COMMIT_NOT_FROM_GRAPH;`
	`97`	`+ c->generation = GENERATION_NUMBER_INFINITY;`
`97`	`98`	`return c;`
`98`	`99`	`}`
`99`	`100`