GIT 0.99.8b
[git/jnareb-git/bp-gitweb.git] / merge-base.c
blob286bf0e8d1522ac4cf01f75343da40ddff6bf6e8
1 #include <stdlib.h>
2 #include "cache.h"
3 #include "commit.h"
5 #define PARENT1 1
6 #define PARENT2 2
7 #define UNINTERESTING 4
9 static struct commit *interesting(struct commit_list *list)
11 while (list) {
12 struct commit *commit = list->item;
13 list = list->next;
14 if (commit->object.flags & UNINTERESTING)
15 continue;
16 return commit;
18 return NULL;
22 * A pathological example of how this thing works.
24 * Suppose we had this commit graph, where chronologically
25 * the timestamp on the commit are A <= B <= C <= D <= E <= F
26 * and we are trying to figure out the merge base for E and F
27 * commits.
29 * F
30 * / \
31 * E A D
32 * \ / /
33 * B /
34 * \ /
35 * C
37 * First we push E and F to list to be processed. E gets bit 1
38 * and F gets bit 2. The list becomes:
40 * list=F(2) E(1), result=empty
42 * Then we pop F, the newest commit, from the list. Its flag is 2.
43 * We scan its parents, mark them reachable from the side that F is
44 * reachable from, and push them to the list:
46 * list=E(1) D(2) A(2), result=empty
48 * Next pop E and do the same.
50 * list=D(2) B(1) A(2), result=empty
52 * Next pop D and do the same.
54 * list=C(2) B(1) A(2), result=empty
56 * Next pop C and do the same.
58 * list=B(1) A(2), result=empty
60 * Now it is B's turn. We mark its parent, C, reachable from B's side,
61 * and push it to the list:
63 * list=C(3) A(2), result=empty
65 * Now pop C and notice it has flags==3. It is placed on the result list,
66 * and the list now contains:
68 * list=A(2), result=C(3)
70 * We pop A and do the same.
72 * list=B(3), result=C(3)
74 * Next, we pop B and something very interesting happens. It has flags==3
75 * so it is also placed on the result list, and its parents are marked
76 * uninteresting, retroactively, and placed back on the list:
78 * list=C(7), result=C(7) B(3)
80 * Now, list does not have any interesting commit. So we find the newest
81 * commit from the result list that is not marked uninteresting. Which is
82 * commit B.
85 static int show_all = 0;
87 static int merge_base(struct commit *rev1, struct commit *rev2)
89 struct commit_list *list = NULL;
90 struct commit_list *result = NULL;
92 if (rev1 == rev2) {
93 printf("%s\n", sha1_to_hex(rev1->object.sha1));
94 return 0;
97 parse_commit(rev1);
98 parse_commit(rev2);
100 rev1->object.flags |= 1;
101 rev2->object.flags |= 2;
102 insert_by_date(rev1, &list);
103 insert_by_date(rev2, &list);
105 while (interesting(list)) {
106 struct commit *commit = list->item;
107 struct commit_list *tmp = list, *parents;
108 int flags = commit->object.flags & 7;
110 list = list->next;
111 free(tmp);
112 if (flags == 3) {
113 insert_by_date(commit, &result);
115 /* Mark parents of a found merge uninteresting */
116 flags |= UNINTERESTING;
118 parents = commit->parents;
119 while (parents) {
120 struct commit *p = parents->item;
121 parents = parents->next;
122 if ((p->object.flags & flags) == flags)
123 continue;
124 parse_commit(p);
125 p->object.flags |= flags;
126 insert_by_date(p, &list);
130 if (!result)
131 return 1;
133 while (result) {
134 struct commit *commit = result->item;
135 result = result->next;
136 if (commit->object.flags & UNINTERESTING)
137 continue;
138 printf("%s\n", sha1_to_hex(commit->object.sha1));
139 if (!show_all)
140 return 0;
141 commit->object.flags |= UNINTERESTING;
143 return 0;
146 static const char merge_base_usage[] =
147 "git-merge-base [--all] <commit-id> <commit-id>";
149 int main(int argc, char **argv)
151 struct commit *rev1, *rev2;
152 unsigned char rev1key[20], rev2key[20];
154 while (1 < argc && argv[1][0] == '-') {
155 char *arg = argv[1];
156 if (!strcmp(arg, "-a") || !strcmp(arg, "--all"))
157 show_all = 1;
158 else
159 usage(merge_base_usage);
160 argc--; argv++;
162 if (argc != 3 ||
163 get_sha1(argv[1], rev1key) ||
164 get_sha1(argv[2], rev2key))
165 usage(merge_base_usage);
166 rev1 = lookup_commit_reference(rev1key);
167 rev2 = lookup_commit_reference(rev2key);
168 if (!rev1 || !rev2)
169 return 1;
170 return merge_base(rev1, rev2);