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commit: add generation number to struct commit

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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 <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee
2018-04-25 14:37:55 +00:00
committed by Junio C Hamano
parent 8fb572af5f
commit 83073cc994
3 changed files with 7 additions and 0 deletions
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4
commit.h
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@ -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;