git/builtin-rev-list.c
Christian Couder 9f199b1595 rev-list: estimate number of bisection step left
This patch teaches "git rev-list --bisect-vars" to output an estimate
of the number of bisection step left _after the current one_ along with
the other variables it already outputs.

This patch also makes "git-bisect.sh" display this number of steps left
_after the current one_, along with the estimate of the number of
revisions left to test (after the current one).

Here is a table to help analyse what should be the best estimate for
the number of bisect steps left.

N : linear case                    --> probabilities --> best
-------------------------------------------------------------
1 : G-B                            --> 0             --> 0
2 : G-U1-B                         --> 0             --> 0
3 : G-U1-U2-B                      --> 0(1/3) 1(2/3) --> 1
4 : G-U1-U2-U3-B                   --> 1             --> 1
5 : G-U1-U2-U3-U4-B                --> 1(3/5) 2(2/5) --> 1
6 : G-U1-U2-U3-U4-U5-B             --> 1(2/6) 2(4/6) --> 2
7 : G-U1-U2-U3-U4-U5-U6-B          --> 1(1/7) 2(6/7) --> 2
8 : G-U1-U2-U3-U4-U5-U6-U7-B       --> 2             --> 2
9 : G-U1-U2-U3-U4-U5-U6-U7-U8-B    --> 2(7/9) 3(2/9) --> 2
10: G-U1-U2-U3-U4-U5-U6-U7-U8-U9-B --> 2(6/10)3(4/10)--> 2

In the column "N", there is the number of revisions that could _now_
be the first bad commit we are looking for.

The "linear case" column describes the linear history corresponding to
the number in column N. G means good, B means bad, and Ux means
unknown. Note that the first bad revision we are looking for can be
any Ux or B.

In the "probabilities" column, there are the different outcomes in
number of steps with the odds of each outcome in parenthesis
corresponding to the linear case.

The "best" column gives the most accurate estimate among the different
outcomes in the "probabilities" column.

We have the following:

best(2^n) == n - 1

and for any x between 0 included and 2^n excluded, the probability for
n - 1 steps left looks like:

P(2^n + x) == (2^n - x) / (2^n + x)

and P(2^n + x) < 0.5 means 2^n < 3x

So the algorithm used in this patch calculates 2^n and x, and then
choose between returning n - 1 and n.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2009-03-04 00:56:52 -08:00

748 lines
17 KiB
C

#include "cache.h"
#include "refs.h"
#include "tag.h"
#include "commit.h"
#include "tree.h"
#include "blob.h"
#include "tree-walk.h"
#include "diff.h"
#include "revision.h"
#include "list-objects.h"
#include "builtin.h"
#include "log-tree.h"
#include "graph.h"
/* bits #0-15 in revision.h */
#define COUNTED (1u<<16)
static const char rev_list_usage[] =
"git rev-list [OPTION] <commit-id>... [ -- paths... ]\n"
" limiting output:\n"
" --max-count=nr\n"
" --max-age=epoch\n"
" --min-age=epoch\n"
" --sparse\n"
" --no-merges\n"
" --remove-empty\n"
" --all\n"
" --branches\n"
" --tags\n"
" --remotes\n"
" --stdin\n"
" --quiet\n"
" ordering output:\n"
" --topo-order\n"
" --date-order\n"
" --reverse\n"
" formatting output:\n"
" --parents\n"
" --children\n"
" --objects | --objects-edge\n"
" --unpacked\n"
" --header | --pretty\n"
" --abbrev=nr | --no-abbrev\n"
" --abbrev-commit\n"
" --left-right\n"
" special purpose:\n"
" --bisect\n"
" --bisect-vars\n"
" --bisect-all"
;
static struct rev_info revs;
static int bisect_list;
static int show_timestamp;
static int hdr_termination;
static const char *header_prefix;
static void finish_commit(struct commit *commit);
static void show_commit(struct commit *commit)
{
graph_show_commit(revs.graph);
if (show_timestamp)
printf("%lu ", commit->date);
if (header_prefix)
fputs(header_prefix, stdout);
if (!revs.graph) {
if (commit->object.flags & BOUNDARY)
putchar('-');
else if (commit->object.flags & UNINTERESTING)
putchar('^');
else if (revs.left_right) {
if (commit->object.flags & SYMMETRIC_LEFT)
putchar('<');
else
putchar('>');
}
}
if (revs.abbrev_commit && revs.abbrev)
fputs(find_unique_abbrev(commit->object.sha1, revs.abbrev),
stdout);
else
fputs(sha1_to_hex(commit->object.sha1), stdout);
if (revs.print_parents) {
struct commit_list *parents = commit->parents;
while (parents) {
printf(" %s", sha1_to_hex(parents->item->object.sha1));
parents = parents->next;
}
}
if (revs.children.name) {
struct commit_list *children;
children = lookup_decoration(&revs.children, &commit->object);
while (children) {
printf(" %s", sha1_to_hex(children->item->object.sha1));
children = children->next;
}
}
show_decorations(&revs, commit);
if (revs.commit_format == CMIT_FMT_ONELINE)
putchar(' ');
else
putchar('\n');
if (revs.verbose_header && commit->buffer) {
struct strbuf buf = STRBUF_INIT;
pretty_print_commit(revs.commit_format, commit,
&buf, revs.abbrev, NULL, NULL,
revs.date_mode, 0);
if (revs.graph) {
if (buf.len) {
if (revs.commit_format != CMIT_FMT_ONELINE)
graph_show_oneline(revs.graph);
graph_show_commit_msg(revs.graph, &buf);
/*
* Add a newline after the commit message.
*
* Usually, this newline produces a blank
* padding line between entries, in which case
* we need to add graph padding on this line.
*
* However, the commit message may not end in a
* newline. In this case the newline simply
* ends the last line of the commit message,
* and we don't need any graph output. (This
* always happens with CMIT_FMT_ONELINE, and it
* happens with CMIT_FMT_USERFORMAT when the
* format doesn't explicitly end in a newline.)
*/
if (buf.len && buf.buf[buf.len - 1] == '\n')
graph_show_padding(revs.graph);
putchar('\n');
} else {
/*
* If the message buffer is empty, just show
* the rest of the graph output for this
* commit.
*/
if (graph_show_remainder(revs.graph))
putchar('\n');
}
} else {
if (buf.len)
printf("%s%c", buf.buf, hdr_termination);
}
strbuf_release(&buf);
} else {
if (graph_show_remainder(revs.graph))
putchar('\n');
}
maybe_flush_or_die(stdout, "stdout");
finish_commit(commit);
}
static void finish_commit(struct commit *commit)
{
if (commit->parents) {
free_commit_list(commit->parents);
commit->parents = NULL;
}
free(commit->buffer);
commit->buffer = NULL;
}
static void finish_object(struct object_array_entry *p)
{
if (p->item->type == OBJ_BLOB && !has_sha1_file(p->item->sha1))
die("missing blob object '%s'", sha1_to_hex(p->item->sha1));
}
static void show_object(struct object_array_entry *p)
{
/* An object with name "foo\n0000000..." can be used to
* confuse downstream "git pack-objects" very badly.
*/
const char *ep = strchr(p->name, '\n');
finish_object(p);
if (ep) {
printf("%s %.*s\n", sha1_to_hex(p->item->sha1),
(int) (ep - p->name),
p->name);
}
else
printf("%s %s\n", sha1_to_hex(p->item->sha1), p->name);
}
static void show_edge(struct commit *commit)
{
printf("-%s\n", sha1_to_hex(commit->object.sha1));
}
/*
* This is a truly stupid algorithm, but it's only
* used for bisection, and we just don't care enough.
*
* We care just barely enough to avoid recursing for
* non-merge entries.
*/
static int count_distance(struct commit_list *entry)
{
int nr = 0;
while (entry) {
struct commit *commit = entry->item;
struct commit_list *p;
if (commit->object.flags & (UNINTERESTING | COUNTED))
break;
if (!(commit->object.flags & TREESAME))
nr++;
commit->object.flags |= COUNTED;
p = commit->parents;
entry = p;
if (p) {
p = p->next;
while (p) {
nr += count_distance(p);
p = p->next;
}
}
}
return nr;
}
static void clear_distance(struct commit_list *list)
{
while (list) {
struct commit *commit = list->item;
commit->object.flags &= ~COUNTED;
list = list->next;
}
}
#define DEBUG_BISECT 0
static inline int weight(struct commit_list *elem)
{
return *((int*)(elem->item->util));
}
static inline void weight_set(struct commit_list *elem, int weight)
{
*((int*)(elem->item->util)) = weight;
}
static int count_interesting_parents(struct commit *commit)
{
struct commit_list *p;
int count;
for (count = 0, p = commit->parents; p; p = p->next) {
if (p->item->object.flags & UNINTERESTING)
continue;
count++;
}
return count;
}
static inline int halfway(struct commit_list *p, int nr)
{
/*
* Don't short-cut something we are not going to return!
*/
if (p->item->object.flags & TREESAME)
return 0;
if (DEBUG_BISECT)
return 0;
/*
* 2 and 3 are halfway of 5.
* 3 is halfway of 6 but 2 and 4 are not.
*/
switch (2 * weight(p) - nr) {
case -1: case 0: case 1:
return 1;
default:
return 0;
}
}
#if !DEBUG_BISECT
#define show_list(a,b,c,d) do { ; } while (0)
#else
static void show_list(const char *debug, int counted, int nr,
struct commit_list *list)
{
struct commit_list *p;
fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
for (p = list; p; p = p->next) {
struct commit_list *pp;
struct commit *commit = p->item;
unsigned flags = commit->object.flags;
enum object_type type;
unsigned long size;
char *buf = read_sha1_file(commit->object.sha1, &type, &size);
char *ep, *sp;
fprintf(stderr, "%c%c%c ",
(flags & TREESAME) ? ' ' : 'T',
(flags & UNINTERESTING) ? 'U' : ' ',
(flags & COUNTED) ? 'C' : ' ');
if (commit->util)
fprintf(stderr, "%3d", weight(p));
else
fprintf(stderr, "---");
fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
for (pp = commit->parents; pp; pp = pp->next)
fprintf(stderr, " %.*s", 8,
sha1_to_hex(pp->item->object.sha1));
sp = strstr(buf, "\n\n");
if (sp) {
sp += 2;
for (ep = sp; *ep && *ep != '\n'; ep++)
;
fprintf(stderr, " %.*s", (int)(ep - sp), sp);
}
fprintf(stderr, "\n");
}
}
#endif /* DEBUG_BISECT */
static struct commit_list *best_bisection(struct commit_list *list, int nr)
{
struct commit_list *p, *best;
int best_distance = -1;
best = list;
for (p = list; p; p = p->next) {
int distance;
unsigned flags = p->item->object.flags;
if (flags & TREESAME)
continue;
distance = weight(p);
if (nr - distance < distance)
distance = nr - distance;
if (distance > best_distance) {
best = p;
best_distance = distance;
}
}
return best;
}
struct commit_dist {
struct commit *commit;
int distance;
};
static int compare_commit_dist(const void *a_, const void *b_)
{
struct commit_dist *a, *b;
a = (struct commit_dist *)a_;
b = (struct commit_dist *)b_;
if (a->distance != b->distance)
return b->distance - a->distance; /* desc sort */
return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
}
static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
{
struct commit_list *p;
struct commit_dist *array = xcalloc(nr, sizeof(*array));
int cnt, i;
for (p = list, cnt = 0; p; p = p->next) {
int distance;
unsigned flags = p->item->object.flags;
if (flags & TREESAME)
continue;
distance = weight(p);
if (nr - distance < distance)
distance = nr - distance;
array[cnt].commit = p->item;
array[cnt].distance = distance;
cnt++;
}
qsort(array, cnt, sizeof(*array), compare_commit_dist);
for (p = list, i = 0; i < cnt; i++) {
struct name_decoration *r = xmalloc(sizeof(*r) + 100);
struct object *obj = &(array[i].commit->object);
sprintf(r->name, "dist=%d", array[i].distance);
r->next = add_decoration(&name_decoration, obj, r);
p->item = array[i].commit;
p = p->next;
}
if (p)
p->next = NULL;
free(array);
return list;
}
/*
* zero or positive weight is the number of interesting commits it can
* reach, including itself. Especially, weight = 0 means it does not
* reach any tree-changing commits (e.g. just above uninteresting one
* but traversal is with pathspec).
*
* weight = -1 means it has one parent and its distance is yet to
* be computed.
*
* weight = -2 means it has more than one parent and its distance is
* unknown. After running count_distance() first, they will get zero
* or positive distance.
*/
static struct commit_list *do_find_bisection(struct commit_list *list,
int nr, int *weights,
int find_all)
{
int n, counted;
struct commit_list *p;
counted = 0;
for (n = 0, p = list; p; p = p->next) {
struct commit *commit = p->item;
unsigned flags = commit->object.flags;
p->item->util = &weights[n++];
switch (count_interesting_parents(commit)) {
case 0:
if (!(flags & TREESAME)) {
weight_set(p, 1);
counted++;
show_list("bisection 2 count one",
counted, nr, list);
}
/*
* otherwise, it is known not to reach any
* tree-changing commit and gets weight 0.
*/
break;
case 1:
weight_set(p, -1);
break;
default:
weight_set(p, -2);
break;
}
}
show_list("bisection 2 initialize", counted, nr, list);
/*
* If you have only one parent in the resulting set
* then you can reach one commit more than that parent
* can reach. So we do not have to run the expensive
* count_distance() for single strand of pearls.
*
* However, if you have more than one parents, you cannot
* just add their distance and one for yourself, since
* they usually reach the same ancestor and you would
* end up counting them twice that way.
*
* So we will first count distance of merges the usual
* way, and then fill the blanks using cheaper algorithm.
*/
for (p = list; p; p = p->next) {
if (p->item->object.flags & UNINTERESTING)
continue;
if (weight(p) != -2)
continue;
weight_set(p, count_distance(p));
clear_distance(list);
/* Does it happen to be at exactly half-way? */
if (!find_all && halfway(p, nr))
return p;
counted++;
}
show_list("bisection 2 count_distance", counted, nr, list);
while (counted < nr) {
for (p = list; p; p = p->next) {
struct commit_list *q;
unsigned flags = p->item->object.flags;
if (0 <= weight(p))
continue;
for (q = p->item->parents; q; q = q->next) {
if (q->item->object.flags & UNINTERESTING)
continue;
if (0 <= weight(q))
break;
}
if (!q)
continue;
/*
* weight for p is unknown but q is known.
* add one for p itself if p is to be counted,
* otherwise inherit it from q directly.
*/
if (!(flags & TREESAME)) {
weight_set(p, weight(q)+1);
counted++;
show_list("bisection 2 count one",
counted, nr, list);
}
else
weight_set(p, weight(q));
/* Does it happen to be at exactly half-way? */
if (!find_all && halfway(p, nr))
return p;
}
}
show_list("bisection 2 counted all", counted, nr, list);
if (!find_all)
return best_bisection(list, nr);
else
return best_bisection_sorted(list, nr);
}
static struct commit_list *find_bisection(struct commit_list *list,
int *reaches, int *all,
int find_all)
{
int nr, on_list;
struct commit_list *p, *best, *next, *last;
int *weights;
show_list("bisection 2 entry", 0, 0, list);
/*
* Count the number of total and tree-changing items on the
* list, while reversing the list.
*/
for (nr = on_list = 0, last = NULL, p = list;
p;
p = next) {
unsigned flags = p->item->object.flags;
next = p->next;
if (flags & UNINTERESTING)
continue;
p->next = last;
last = p;
if (!(flags & TREESAME))
nr++;
on_list++;
}
list = last;
show_list("bisection 2 sorted", 0, nr, list);
*all = nr;
weights = xcalloc(on_list, sizeof(*weights));
/* Do the real work of finding bisection commit. */
best = do_find_bisection(list, nr, weights, find_all);
if (best) {
if (!find_all)
best->next = NULL;
*reaches = weight(best);
}
free(weights);
return best;
}
static inline int log2i(int n)
{
int log2 = 0;
for (; n > 1; n >>= 1)
log2++;
return log2;
}
static inline int exp2i(int n)
{
return 1 << n;
}
/*
* Estimate the number of bisect steps left (after the current step)
*
* For any x between 0 included and 2^n excluded, the probability for
* n - 1 steps left looks like:
*
* P(2^n + x) == (2^n - x) / (2^n + x)
*
* and P(2^n + x) < 0.5 means 2^n < 3x
*/
static int estimate_bisect_steps(int all)
{
int n, x, e;
if (all < 3)
return 0;
n = log2i(all);
e = exp2i(n);
x = all - e;
return (e < 3 * x) ? n : n - 1;
}
int cmd_rev_list(int argc, const char **argv, const char *prefix)
{
struct commit_list *list;
int i;
int read_from_stdin = 0;
int bisect_show_vars = 0;
int bisect_find_all = 0;
int quiet = 0;
git_config(git_default_config, NULL);
init_revisions(&revs, prefix);
revs.abbrev = 0;
revs.commit_format = CMIT_FMT_UNSPECIFIED;
argc = setup_revisions(argc, argv, &revs, NULL);
quiet = DIFF_OPT_TST(&revs.diffopt, QUIET);
for (i = 1 ; i < argc; i++) {
const char *arg = argv[i];
if (!strcmp(arg, "--header")) {
revs.verbose_header = 1;
continue;
}
if (!strcmp(arg, "--timestamp")) {
show_timestamp = 1;
continue;
}
if (!strcmp(arg, "--bisect")) {
bisect_list = 1;
continue;
}
if (!strcmp(arg, "--bisect-all")) {
bisect_list = 1;
bisect_find_all = 1;
revs.show_decorations = 1;
continue;
}
if (!strcmp(arg, "--bisect-vars")) {
bisect_list = 1;
bisect_show_vars = 1;
continue;
}
if (!strcmp(arg, "--stdin")) {
if (read_from_stdin++)
die("--stdin given twice?");
read_revisions_from_stdin(&revs);
continue;
}
usage(rev_list_usage);
}
if (revs.commit_format != CMIT_FMT_UNSPECIFIED) {
/* The command line has a --pretty */
hdr_termination = '\n';
if (revs.commit_format == CMIT_FMT_ONELINE)
header_prefix = "";
else
header_prefix = "commit ";
}
else if (revs.verbose_header)
/* Only --header was specified */
revs.commit_format = CMIT_FMT_RAW;
list = revs.commits;
if ((!list &&
(!(revs.tag_objects||revs.tree_objects||revs.blob_objects) &&
!revs.pending.nr)) ||
revs.diff)
usage(rev_list_usage);
save_commit_buffer = revs.verbose_header ||
revs.grep_filter.pattern_list;
if (bisect_list)
revs.limited = 1;
if (prepare_revision_walk(&revs))
die("revision walk setup failed");
if (revs.tree_objects)
mark_edges_uninteresting(revs.commits, &revs, show_edge);
if (bisect_list) {
int reaches = reaches, all = all;
revs.commits = find_bisection(revs.commits, &reaches, &all,
bisect_find_all);
if (bisect_show_vars) {
int cnt;
char hex[41];
if (!revs.commits)
return 1;
/*
* revs.commits can reach "reaches" commits among
* "all" commits. If it is good, then there are
* (all-reaches) commits left to be bisected.
* On the other hand, if it is bad, then the set
* to bisect is "reaches".
* A bisect set of size N has (N-1) commits further
* to test, as we already know one bad one.
*/
cnt = all - reaches;
if (cnt < reaches)
cnt = reaches;
strcpy(hex, sha1_to_hex(revs.commits->item->object.sha1));
if (bisect_find_all) {
traverse_commit_list(&revs, show_commit, show_object);
printf("------\n");
}
printf("bisect_rev=%s\n"
"bisect_nr=%d\n"
"bisect_good=%d\n"
"bisect_bad=%d\n"
"bisect_all=%d\n"
"bisect_steps=%d\n",
hex,
cnt - 1,
all - reaches - 1,
reaches - 1,
all,
estimate_bisect_steps(all));
return 0;
}
}
traverse_commit_list(&revs,
quiet ? finish_commit : show_commit,
quiet ? finish_object : show_object);
return 0;
}