pseudo-merge.c

   1 #define USE_THE_REPOSITORY_VARIABLE
   2
   3 #include "git-compat-util.h"
   4 #include "pseudo-merge.h"
   5 #include "date.h"
   6 #include "oid-array.h"
   7 #include "strbuf.h"
   8 #include "config.h"
   9 #include "string-list.h"
  10 #include "refs.h"
  11 #include "pack-bitmap.h"
  12 #include "commit.h"
  13 #include "alloc.h"
  14 #include "progress.h"
  15 #include "hex.h"
  16
  17 #define DEFAULT_PSEUDO_MERGE_DECAY 1.0
  18 #define DEFAULT_PSEUDO_MERGE_MAX_MERGES 64
  19 #define DEFAULT_PSEUDO_MERGE_SAMPLE_RATE 1
  20 #define DEFAULT_PSEUDO_MERGE_THRESHOLD approxidate("1.week.ago")
  21 #define DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD approxidate("1.month.ago")
  22 #define DEFAULT_PSEUDO_MERGE_STABLE_SIZE 512
  23
  24 static double gitexp(double base, int exp)
  25 {
  26         double result = 1;
  27         while (1) {
  28                 if (exp % 2)
  29                         result *= base;
  30                 exp >>= 1;
  31                 if (!exp)
  32                         break;
  33                 base *= base;
  34         }
  35         return result;
  36 }
  37
  38 static uint32_t pseudo_merge_group_size(const struct pseudo_merge_group *group,
  39                                         const struct pseudo_merge_matches *matches,
  40                                         uint32_t i)
  41 {
  42         double C = 0.0f;
  43         uint32_t n;
  44
  45         /*
  46          * The size of pseudo-merge groups decays according to a power series,
  47          * which looks like:
  48          *
  49          *   f(n) = C * n^-k
  50          *
  51          * , where 'n' is the n-th pseudo-merge group, 'f(n)' is its size, 'k'
  52          * is the decay rate, and 'C' is a scaling value.
  53          *
  54          * The value of C depends on the number of groups, decay rate, and total
  55          * number of commits. It is computed such that if there are M and N
  56          * total groups and commits, respectively, that:
  57          *
  58          *   N = f(0) + f(1) + ... f(M-1)
  59          *
  60          * Rearranging to isolate C, we get:
  61          *
  62          *   N = \sum_{n=1}^M C / n^k
  63          *
  64          *   N / C = \sum_{n=1}^M n^-k
  65          *
  66          *   C = N / \sum_{n=1}^M n^-k
  67          *
  68          * For example, if we have a decay rate of 'k' being equal to 1.5, 'N'
  69          * total commits equal to 10,000, and 'M' being equal to 6 groups, then
  70          * the (rounded) group sizes are:
  71          *
  72          *   { 5469, 1934, 1053, 684, 489, 372 }
  73          *
  74          * increasing the number of total groups, say to 10, scales the group
  75          * sizes appropriately:
  76          *
  77          *   { 5012, 1772, 964, 626, 448, 341, 271, 221, 186, 158 }
  78          */
  79         for (n = 0; n < group->max_merges; n++)
  80                 C += 1.0 / gitexp(n + 1, group->decay);
  81         C = matches->unstable_nr / C;
  82
  83         return (uint32_t)((C / gitexp(i + 1, group->decay)) + 0.5);
  84 }
  85
  86 static void pseudo_merge_group_init(struct pseudo_merge_group *group)
  87 {
  88         memset(group, 0, sizeof(struct pseudo_merge_group));
  89
  90         strmap_init_with_options(&group->matches, NULL, 0);
  91
  92         group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
  93         group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
  94         group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
  95         group->threshold = DEFAULT_PSEUDO_MERGE_THRESHOLD;
  96         group->stable_threshold = DEFAULT_PSEUDO_MERGE_STABLE_THRESHOLD;
  97         group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
  98 }
  99
 100 static int pseudo_merge_config(const char *var, const char *value,
 101                                const struct config_context *ctx,
 102                                void *cb_data)
 103 {
 104         struct string_list *list = cb_data;
 105         struct string_list_item *item;
 106         struct pseudo_merge_group *group;
 107         struct strbuf buf = STRBUF_INIT;
 108         const char *sub, *key;
 109         size_t sub_len;
 110         int ret = 0;
 111
 112         if (parse_config_key(var, "bitmappseudomerge", &sub, &sub_len, &key))
 113                 goto done;
 114
 115         if (!sub_len)
 116                 goto done;
 117
 118         strbuf_add(&buf, sub, sub_len);
 119
 120         item = string_list_lookup(list, buf.buf);
 121         if (!item) {
 122                 item = string_list_insert(list, buf.buf);
 123
 124                 item->util = xmalloc(sizeof(struct pseudo_merge_group));
 125                 pseudo_merge_group_init(item->util);
 126         }
 127
 128         group = item->util;
 129
 130         if (!strcmp(key, "pattern")) {
 131                 struct strbuf re = STRBUF_INIT;
 132
 133                 free(group->pattern);
 134                 if (*value != '^')
 135                         strbuf_addch(&re, '^');
 136                 strbuf_addstr(&re, value);
 137
 138                 group->pattern = xcalloc(1, sizeof(regex_t));
 139                 if (regcomp(group->pattern, re.buf, REG_EXTENDED))
 140                         die(_("failed to load pseudo-merge regex for %s: '%s'"),
 141                             sub, re.buf);
 142
 143                 strbuf_release(&re);
 144         } else if (!strcmp(key, "decay")) {
 145                 group->decay = git_config_double(var, value, ctx->kvi);
 146                 if (group->decay < 0) {
 147                         warning(_("%s must be non-negative, using default"), var);
 148                         group->decay = DEFAULT_PSEUDO_MERGE_DECAY;
 149                 }
 150         } else if (!strcmp(key, "samplerate")) {
 151                 group->sample_rate = git_config_double(var, value, ctx->kvi);
 152                 if (!(0 <= group->sample_rate && group->sample_rate <= 1)) {
 153                         warning(_("%s must be between 0 and 1, using default"), var);
 154                         group->sample_rate = DEFAULT_PSEUDO_MERGE_SAMPLE_RATE;
 155                 }
 156         } else if (!strcmp(key, "threshold")) {
 157                 if (git_config_expiry_date(&group->threshold, var, value)) {
 158                         ret = -1;
 159                         goto done;
 160                 }
 161         } else if (!strcmp(key, "maxmerges")) {
 162                 group->max_merges = git_config_int(var, value, ctx->kvi);
 163                 if (group->max_merges < 0) {
 164                         warning(_("%s must be non-negative, using default"), var);
 165                         group->max_merges = DEFAULT_PSEUDO_MERGE_MAX_MERGES;
 166                 }
 167         } else if (!strcmp(key, "stablethreshold")) {
 168                 if (git_config_expiry_date(&group->stable_threshold, var, value)) {
 169                         ret = -1;
 170                         goto done;
 171                 }
 172         } else if (!strcmp(key, "stablesize")) {
 173                 group->stable_size = git_config_int(var, value, ctx->kvi);
 174                 if (group->stable_size <= 0) {
 175                         warning(_("%s must be positive, using default"), var);
 176                         group->stable_size = DEFAULT_PSEUDO_MERGE_STABLE_SIZE;
 177                 }
 178         }
 179
 180 done:
 181         strbuf_release(&buf);
 182
 183         return ret;
 184 }
 185
 186 void load_pseudo_merges_from_config(struct string_list *list)
 187 {
 188         struct string_list_item *item;
 189
 190         git_config(pseudo_merge_config, list);
 191
 192         for_each_string_list_item(item, list) {
 193                 struct pseudo_merge_group *group = item->util;
 194                 if (!group->pattern)
 195                         die(_("pseudo-merge group '%s' missing required pattern"),
 196                             item->string);
 197                 if (group->threshold < group->stable_threshold)
 198                         die(_("pseudo-merge group '%s' has unstable threshold "
 199                               "before stable one"), item->string);
 200         }
 201 }
 202
 203 static int find_pseudo_merge_group_for_ref(const char *refname,
 204                                            const struct object_id *oid,
 205                                            int flags UNUSED,
 206                                            void *_data)
 207 {
 208         struct bitmap_writer *writer = _data;
 209         struct object_id peeled;
 210         struct commit *c;
 211         uint32_t i;
 212         int has_bitmap;
 213
 214         if (!peel_iterated_oid(the_repository, oid, &peeled))
 215                 oid = &peeled;
 216
 217         c = lookup_commit(the_repository, oid);
 218         if (!c)
 219                 return 0;
 220
 221         has_bitmap = bitmap_writer_has_bitmapped_object_id(writer, oid);
 222
 223         for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
 224                 struct pseudo_merge_group *group;
 225                 struct pseudo_merge_matches *matches;
 226                 struct strbuf group_name = STRBUF_INIT;
 227                 regmatch_t captures[16];
 228                 size_t j;
 229
 230                 group = writer->pseudo_merge_groups.items[i].util;
 231                 if (regexec(group->pattern, refname, ARRAY_SIZE(captures),
 232                             captures, 0))
 233                         continue;
 234
 235                 if (captures[ARRAY_SIZE(captures) - 1].rm_so != -1)
 236                         warning(_("pseudo-merge regex from config has too many capture "
 237                                   "groups (max=%"PRIuMAX")"),
 238                                 (uintmax_t)ARRAY_SIZE(captures) - 2);
 239
 240                 for (j = !!group->pattern->re_nsub; j < ARRAY_SIZE(captures); j++) {
 241                         regmatch_t *match = &captures[j];
 242                         if (match->rm_so == -1)
 243                                 continue;
 244
 245                         if (group_name.len)
 246                                 strbuf_addch(&group_name, '-');
 247
 248                         strbuf_add(&group_name, refname + match->rm_so,
 249                                    match->rm_eo - match->rm_so);
 250                 }
 251
 252                 matches = strmap_get(&group->matches, group_name.buf);
 253                 if (!matches) {
 254                         matches = xcalloc(1, sizeof(*matches));
 255                         strmap_put(&group->matches, strbuf_detach(&group_name, NULL),
 256                                    matches);
 257                 }
 258
 259                 if (c->date <= group->stable_threshold) {
 260                         ALLOC_GROW(matches->stable, matches->stable_nr + 1,
 261                                    matches->stable_alloc);
 262                         matches->stable[matches->stable_nr++] = c;
 263                 } else if (c->date <= group->threshold && !has_bitmap) {
 264                         ALLOC_GROW(matches->unstable, matches->unstable_nr + 1,
 265                                    matches->unstable_alloc);
 266                         matches->unstable[matches->unstable_nr++] = c;
 267                 }
 268
 269                 strbuf_release(&group_name);
 270         }
 271
 272         return 0;
 273 }
 274
 275 static struct commit *push_pseudo_merge(struct pseudo_merge_group *group)
 276 {
 277         struct commit *merge;
 278
 279         ALLOC_GROW(group->merges, group->merges_nr + 1, group->merges_alloc);
 280
 281         merge = alloc_commit_node(the_repository);
 282         merge->object.parsed = 1;
 283         merge->object.flags |= BITMAP_PSEUDO_MERGE;
 284
 285         group->merges[group->merges_nr++] = merge;
 286
 287         return merge;
 288 }
 289
 290 static struct pseudo_merge_commit_idx *pseudo_merge_idx(kh_oid_map_t *pseudo_merge_commits,
 291                                                         const struct object_id *oid)
 292
 293 {
 294         struct pseudo_merge_commit_idx *pmc;
 295         int hash_ret;
 296         khiter_t hash_pos = kh_put_oid_map(pseudo_merge_commits, *oid,
 297                                            &hash_ret);
 298
 299         if (hash_ret) {
 300                 CALLOC_ARRAY(pmc, 1);
 301                 kh_value(pseudo_merge_commits, hash_pos) = pmc;
 302         } else {
 303                 pmc = kh_value(pseudo_merge_commits, hash_pos);
 304         }
 305
 306         return pmc;
 307 }
 308
 309 #define MIN_PSEUDO_MERGE_SIZE 8
 310
 311 static void select_pseudo_merges_1(struct bitmap_writer *writer,
 312                                    struct pseudo_merge_group *group,
 313                                    struct pseudo_merge_matches *matches)
 314 {
 315         uint32_t i, j;
 316         uint32_t stable_merges_nr;
 317
 318         if (!matches->stable_nr && !matches->unstable_nr)
 319                 return; /* all tips in this group already have bitmaps */
 320
 321         stable_merges_nr = matches->stable_nr / group->stable_size;
 322         if (matches->stable_nr % group->stable_size)
 323                 stable_merges_nr++;
 324
 325         /* make stable_merges_nr pseudo merges for stable commits */
 326         for (i = 0, j = 0; i < stable_merges_nr; i++) {
 327                 struct commit *merge;
 328                 struct commit_list **p;
 329
 330                 merge = push_pseudo_merge(group);
 331                 p = &merge->parents;
 332
 333                 /*
 334                  * For each pseudo-merge created above, add parents to the
 335                  * allocated commit node from the stable set of commits
 336                  * (un-bitmapped, newer than the stable threshold).
 337                  */
 338                 do {
 339                         struct commit *c;
 340                         struct pseudo_merge_commit_idx *pmc;
 341
 342                         if (j >= matches->stable_nr)
 343                                 break;
 344
 345                         c = matches->stable[j++];
 346                         /*
 347                          * Here and below, make sure that we keep our mapping of
 348                          * commits -> pseudo-merge(s) which include the key'd
 349                          * commit up-to-date.
 350                          */
 351                         pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
 352                                                &c->object.oid);
 353
 354                         ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);
 355
 356                         pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
 357                         p = commit_list_append(c, p);
 358                 } while (j % group->stable_size);
 359
 360                 bitmap_writer_push_commit(writer, merge, 1);
 361                 writer->pseudo_merges_nr++;
 362         }
 363
 364         /* make up to group->max_merges pseudo merges for unstable commits */
 365         for (i = 0, j = 0; i < group->max_merges; i++) {
 366                 struct commit *merge;
 367                 struct commit_list **p;
 368                 uint32_t size, end;
 369
 370                 merge = push_pseudo_merge(group);
 371                 p = &merge->parents;
 372
 373                 size = pseudo_merge_group_size(group, matches, i);
 374                 end = size < MIN_PSEUDO_MERGE_SIZE ? matches->unstable_nr : j + size;
 375
 376                 /*
 377                  * For each pseudo-merge commit created above, add parents to
 378                  * the allocated commit node from the unstable set of commits
 379                  * (newer than the stable threshold).
 380                  *
 381                  * Account for the sample rate, since not every candidate from
 382                  * the set of stable commits will be included as a pseudo-merge
 383                  * parent.
 384                  */
 385                 for (; j < end && j < matches->unstable_nr; j++) {
 386                         struct commit *c = matches->unstable[j];
 387                         struct pseudo_merge_commit_idx *pmc;
 388
 389                         if (j % (uint32_t)(1.0 / group->sample_rate))
 390                                 continue;
 391
 392                         pmc = pseudo_merge_idx(writer->pseudo_merge_commits,
 393                                                &c->object.oid);
 394
 395                         ALLOC_GROW(pmc->pseudo_merge, pmc->nr + 1, pmc->alloc);
 396
 397                         pmc->pseudo_merge[pmc->nr++] = writer->pseudo_merges_nr;
 398                         p = commit_list_append(c, p);
 399                 }
 400
 401                 bitmap_writer_push_commit(writer, merge, 1);
 402                 writer->pseudo_merges_nr++;
 403                 if (end >= matches->unstable_nr)
 404                         break;
 405         }
 406 }
 407
 408 static int commit_date_cmp(const void *va, const void *vb)
 409 {
 410         timestamp_t a = (*(const struct commit **)va)->date;
 411         timestamp_t b = (*(const struct commit **)vb)->date;
 412
 413         if (a < b)
 414                 return -1;
 415         else if (a > b)
 416                 return 1;
 417         return 0;
 418 }
 419
 420 static void sort_pseudo_merge_matches(struct pseudo_merge_matches *matches)
 421 {
 422         QSORT(matches->stable, matches->stable_nr, commit_date_cmp);
 423         QSORT(matches->unstable, matches->unstable_nr, commit_date_cmp);
 424 }
 425
 426 void select_pseudo_merges(struct bitmap_writer *writer,
 427                           struct commit **commits, size_t commits_nr)
 428 {
 429         struct progress *progress = NULL;
 430         uint32_t i;
 431
 432         if (!writer->pseudo_merge_groups.nr)
 433                 return;
 434
 435         if (writer->show_progress)
 436                 progress = start_progress("Selecting pseudo-merge commits",
 437                                           writer->pseudo_merge_groups.nr);
 438
 439         refs_for_each_ref(get_main_ref_store(the_repository),
 440                           find_pseudo_merge_group_for_ref, writer);
 441
 442         for (i = 0; i < writer->pseudo_merge_groups.nr; i++) {
 443                 struct pseudo_merge_group *group;
 444                 struct hashmap_iter iter;
 445                 struct strmap_entry *e;
 446
 447                 group = writer->pseudo_merge_groups.items[i].util;
 448                 strmap_for_each_entry(&group->matches, &iter, e) {
 449                         struct pseudo_merge_matches *matches = e->value;
 450
 451                         sort_pseudo_merge_matches(matches);
 452
 453                         select_pseudo_merges_1(writer, group, matches);
 454                 }
 455
 456                 display_progress(progress, i + 1);
 457         }
 458
 459         stop_progress(&progress);
 460 }
 461
 462 void free_pseudo_merge_map(struct pseudo_merge_map *pm)
 463 {
 464         uint32_t i;
 465         for (i = 0; i < pm->nr; i++) {
 466                 ewah_pool_free(pm->v[i].commits);
 467                 ewah_pool_free(pm->v[i].bitmap);
 468         }
 469         free(pm->v);
 470 }
 471
 472 struct pseudo_merge_commit_ext {
 473         uint32_t nr;
 474         const unsigned char *ptr;
 475 };
 476
 477 static int pseudo_merge_ext_at(const struct pseudo_merge_map *pm,
 478                                struct pseudo_merge_commit_ext *ext, size_t at)
 479 {
 480         if (at >= pm->map_size)
 481                 return error(_("extended pseudo-merge read out-of-bounds "
 482                                "(%"PRIuMAX" >= %"PRIuMAX")"),
 483                              (uintmax_t)at, (uintmax_t)pm->map_size);
 484         if (at + 4 >= pm->map_size)
 485                 return error(_("extended pseudo-merge entry is too short "
 486                                "(%"PRIuMAX" >= %"PRIuMAX")"),
 487                              (uintmax_t)(at + 4), (uintmax_t)pm->map_size);
 488
 489         ext->nr = get_be32(pm->map + at);
 490         ext->ptr = pm->map + at + sizeof(uint32_t);
 491
 492         return 0;
 493 }
 494
 495 struct ewah_bitmap *pseudo_merge_bitmap(const struct pseudo_merge_map *pm,
 496                                         struct pseudo_merge *merge)
 497 {
 498         if (!merge->loaded_commits)
 499                 BUG("cannot use unloaded pseudo-merge bitmap");
 500
 501         if (!merge->loaded_bitmap) {
 502                 size_t at = merge->bitmap_at;
 503
 504                 merge->bitmap = read_bitmap(pm->map, pm->map_size, &at);
 505                 merge->loaded_bitmap = 1;
 506         }
 507
 508         return merge->bitmap;
 509 }
 510
 511 struct pseudo_merge *use_pseudo_merge(const struct pseudo_merge_map *pm,
 512                                       struct pseudo_merge *merge)
 513 {
 514         if (!merge->loaded_commits) {
 515                 size_t pos = merge->at;
 516
 517                 merge->commits = read_bitmap(pm->map, pm->map_size, &pos);
 518                 merge->bitmap_at = pos;
 519                 merge->loaded_commits = 1;
 520         }
 521         return merge;
 522 }
 523
 524 static struct pseudo_merge *pseudo_merge_at(const struct pseudo_merge_map *pm,
 525                                             struct object_id *oid,
 526                                             size_t want)
 527 {
 528         size_t lo = 0;
 529         size_t hi = pm->nr;
 530
 531         while (lo < hi) {
 532                 size_t mi = lo + (hi - lo) / 2;
 533                 size_t got = pm->v[mi].at;
 534
 535                 if (got == want)
 536                         return use_pseudo_merge(pm, &pm->v[mi]);
 537                 else if (got < want)
 538                         hi = mi;
 539                 else
 540                         lo = mi + 1;
 541         }
 542
 543         warning(_("could not find pseudo-merge for commit %s at offset %"PRIuMAX),
 544                 oid_to_hex(oid), (uintmax_t)want);
 545
 546         return NULL;
 547 }
 548
 549 struct pseudo_merge_commit {
 550         uint32_t commit_pos;
 551         uint64_t pseudo_merge_ofs;
 552 };
 553
 554 #define PSEUDO_MERGE_COMMIT_RAWSZ (sizeof(uint32_t)+sizeof(uint64_t))
 555
 556 static void read_pseudo_merge_commit_at(struct pseudo_merge_commit *merge,
 557                                         const unsigned char *at)
 558 {
 559         merge->commit_pos = get_be32(at);
 560         merge->pseudo_merge_ofs = get_be64(at + sizeof(uint32_t));
 561 }
 562
 563 static int nth_pseudo_merge_ext(const struct pseudo_merge_map *pm,
 564                                 struct pseudo_merge_commit_ext *ext,
 565                                 struct pseudo_merge_commit *merge,
 566                                 uint32_t n)
 567 {
 568         size_t ofs;
 569
 570         if (n >= ext->nr)
 571                 return error(_("extended pseudo-merge lookup out-of-bounds "
 572                                "(%"PRIu32" >= %"PRIu32")"), n, ext->nr);
 573
 574         ofs = get_be64(ext->ptr + st_mult(n, sizeof(uint64_t)));
 575         if (ofs >= pm->map_size)
 576                 return error(_("out-of-bounds read: (%"PRIuMAX" >= %"PRIuMAX")"),
 577                              (uintmax_t)ofs, (uintmax_t)pm->map_size);
 578
 579         read_pseudo_merge_commit_at(merge, pm->map + ofs);
 580
 581         return 0;
 582 }
 583
 584 static unsigned apply_pseudo_merge(const struct pseudo_merge_map *pm,
 585                                    struct pseudo_merge *merge,
 586                                    struct bitmap *result,
 587                                    struct bitmap *roots)
 588 {
 589         if (merge->satisfied)
 590                 return 0;
 591
 592         if (!ewah_bitmap_is_subset(merge->commits, roots ? roots : result))
 593                 return 0;
 594
 595         bitmap_or_ewah(result, pseudo_merge_bitmap(pm, merge));
 596         if (roots)
 597                 bitmap_or_ewah(roots, pseudo_merge_bitmap(pm, merge));
 598         merge->satisfied = 1;
 599
 600         return 1;
 601 }
 602
 603 static int pseudo_merge_commit_cmp(const void *va, const void *vb)
 604 {
 605         struct pseudo_merge_commit merge;
 606         uint32_t key = *(uint32_t*)va;
 607
 608         read_pseudo_merge_commit_at(&merge, vb);
 609
 610         if (key < merge.commit_pos)
 611                 return -1;
 612         if (key > merge.commit_pos)
 613                 return 1;
 614         return 0;
 615 }
 616
 617 static struct pseudo_merge_commit *find_pseudo_merge(const struct pseudo_merge_map *pm,
 618                                                      uint32_t pos)
 619 {
 620         if (!pm->commits_nr)
 621                 return NULL;
 622
 623         return bsearch(&pos, pm->commits, pm->commits_nr,
 624                        PSEUDO_MERGE_COMMIT_RAWSZ, pseudo_merge_commit_cmp);
 625 }
 626
 627 int apply_pseudo_merges_for_commit(const struct pseudo_merge_map *pm,
 628                                    struct bitmap *result,
 629                                    struct commit *commit, uint32_t commit_pos)
 630 {
 631         struct pseudo_merge *merge;
 632         struct pseudo_merge_commit *merge_commit;
 633         int ret = 0;
 634
 635         merge_commit = find_pseudo_merge(pm, commit_pos);
 636         if (!merge_commit)
 637                 return 0;
 638
 639         if (merge_commit->pseudo_merge_ofs & ((uint64_t)1<<63)) {
 640                 struct pseudo_merge_commit_ext ext = { 0 };
 641                 off_t ofs = merge_commit->pseudo_merge_ofs & ~((uint64_t)1<<63);
 642                 uint32_t i;
 643
 644                 if (pseudo_merge_ext_at(pm, &ext, ofs) < -1) {
 645                         warning(_("could not read extended pseudo-merge table "
 646                                   "for commit %s"),
 647                                 oid_to_hex(&commit->object.oid));
 648                         return ret;
 649                 }
 650
 651                 for (i = 0; i < ext.nr; i++) {
 652                         if (nth_pseudo_merge_ext(pm, &ext, merge_commit, i) < 0)
 653                                 return ret;
 654
 655                         merge = pseudo_merge_at(pm, &commit->object.oid,
 656                                                 merge_commit->pseudo_merge_ofs);
 657
 658                         if (!merge)
 659                                 return ret;
 660
 661                         if (apply_pseudo_merge(pm, merge, result, NULL))
 662                                 ret++;
 663                 }
 664         } else {
 665                 merge = pseudo_merge_at(pm, &commit->object.oid,
 666                                         merge_commit->pseudo_merge_ofs);
 667
 668                 if (!merge)
 669                         return ret;
 670
 671                 if (apply_pseudo_merge(pm, merge, result, NULL))
 672                         ret++;
 673         }
 674
 675         if (ret)
 676                 cascade_pseudo_merges(pm, result, NULL);
 677
 678         return ret;
 679 }
 680
 681 int cascade_pseudo_merges(const struct pseudo_merge_map *pm,
 682                           struct bitmap *result,
 683                           struct bitmap *roots)
 684 {
 685         unsigned any_satisfied;
 686         int ret = 0;
 687
 688         do {
 689                 struct pseudo_merge *merge;
 690                 uint32_t i;
 691
 692                 any_satisfied = 0;
 693
 694                 for (i = 0; i < pm->nr; i++) {
 695                         merge = use_pseudo_merge(pm, &pm->v[i]);
 696                         if (apply_pseudo_merge(pm, merge, result, roots)) {
 697                                 any_satisfied |= 1;
 698                                 ret++;
 699                         }
 700                 }
 701         } while (any_satisfied);
 702
 703         return ret;
 704 }
 705
 706 struct pseudo_merge *pseudo_merge_for_parents(const struct pseudo_merge_map *pm,
 707                                               struct bitmap *parents)
 708 {
 709         struct pseudo_merge *match = NULL;
 710         size_t i;
 711
 712         if (!pm->nr)
 713                 return NULL;
 714
 715         /*
 716          * NOTE: this loop is quadratic in the worst-case (where no
 717          * matching pseudo-merge bitmaps are found), but in practice
 718          * this is OK for a few reasons:
 719          *
 720          *   - Rejecting pseudo-merge bitmaps that do not match the
 721          *     given commit is done quickly (i.e. `bitmap_equals_ewah()`
 722          *     returns early when we know the two bitmaps aren't equal.
 723          *
 724          *   - Already matched pseudo-merge bitmaps (which we track with
 725          *     the `->satisfied` bit here) are skipped as potential
 726          *     candidates.
 727          *
 728          *   - The number of pseudo-merges should be small (in the
 729          *     hundreds for most repositories).
 730          *
 731          * If in the future this semi-quadratic behavior does become a
 732          * problem, another approach would be to keep track of which
 733          * pseudo-merges are still "viable" after enumerating the
 734          * pseudo-merge commit's parents:
 735          *
 736          *   - A pseudo-merge bitmap becomes non-viable when the bit(s)
 737          *     corresponding to one or more parent(s) of the given
 738          *     commit are not set in a candidate pseudo-merge's commits
 739          *     bitmap.
 740          *
 741          *   - After processing all bits, enumerate the remaining set of
 742          *     viable pseudo-merge bitmaps, and check that their
 743          *     popcount() matches the number of parents in the given
 744          *     commit.
 745          */
 746         for (i = 0; i < pm->nr; i++) {
 747                 struct pseudo_merge *candidate = use_pseudo_merge(pm, &pm->v[i]);
 748                 if (!candidate || candidate->satisfied)
 749                         continue;
 750                 if (!bitmap_equals_ewah(parents, candidate->commits))
 751                         continue;
 752
 753                 match = candidate;
 754                 match->satisfied = 1;
 755                 break;
 756         }
 757
 758         return match;
 759 }