diffcore-break.con commit Do not link with -lcrypto under NO_OPENSSL (5b02b9b)
   1/*
   2 * Copyright (C) 2005 Junio C Hamano
   3 */
   4#include "cache.h"
   5#include "diff.h"
   6#include "diffcore.h"
   7
   8static int should_break(struct diff_filespec *src,
   9                        struct diff_filespec *dst,
  10                        int break_score,
  11                        int *merge_score_p)
  12{
  13        /* dst is recorded as a modification of src.  Are they so
  14         * different that we are better off recording this as a pair
  15         * of delete and create?
  16         *
  17         * There are two criteria used in this algorithm.  For the
  18         * purposes of helping later rename/copy, we take both delete
  19         * and insert into account and estimate the amount of "edit".
  20         * If the edit is very large, we break this pair so that
  21         * rename/copy can pick the pieces up to match with other
  22         * files.
  23         *
  24         * On the other hand, we would want to ignore inserts for the
  25         * pure "complete rewrite" detection.  As long as most of the
  26         * existing contents were removed from the file, it is a
  27         * complete rewrite, and if sizable chunk from the original
  28         * still remains in the result, it is not a rewrite.  It does
  29         * not matter how much or how little new material is added to
  30         * the file.
  31         *
  32         * The score we leave for such a broken filepair uses the
  33         * latter definition so that later clean-up stage can find the
  34         * pieces that should not have been broken according to the
  35         * latter definition after rename/copy runs, and merge the
  36         * broken pair that have a score lower than given criteria
  37         * back together.  The break operation itself happens
  38         * according to the former definition.
  39         *
  40         * The minimum_edit parameter tells us when to break (the
  41         * amount of "edit" required for us to consider breaking the
  42         * pair).  We leave the amount of deletion in *merge_score_p
  43         * when we return.
  44         *
  45         * The value we return is 1 if we want the pair to be broken,
  46         * or 0 if we do not.
  47         */
  48        unsigned long delta_size, max_size;
  49        unsigned long src_copied, literal_added, src_removed;
  50
  51        *merge_score_p = 0; /* assume no deletion --- "do not break"
  52                             * is the default.
  53                             */
  54
  55        if (S_ISREG(src->mode) != S_ISREG(dst->mode)) {
  56                *merge_score_p = (int)MAX_SCORE;
  57                return 1; /* even their types are different */
  58        }
  59
  60        if (src->sha1_valid && dst->sha1_valid &&
  61            !hashcmp(src->sha1, dst->sha1))
  62                return 0; /* they are the same */
  63
  64        if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0))
  65                return 0; /* error but caught downstream */
  66
  67        max_size = ((src->size > dst->size) ? src->size : dst->size);
  68        if (max_size < MINIMUM_BREAK_SIZE)
  69                return 0; /* we do not break too small filepair */
  70
  71        if (diffcore_count_changes(src, dst,
  72                                   &src->cnt_data, &dst->cnt_data,
  73                                   0,
  74                                   &src_copied, &literal_added))
  75                return 0;
  76
  77        /* sanity */
  78        if (src->size < src_copied)
  79                src_copied = src->size;
  80        if (dst->size < literal_added + src_copied) {
  81                if (src_copied < dst->size)
  82                        literal_added = dst->size - src_copied;
  83                else
  84                        literal_added = 0;
  85        }
  86        src_removed = src->size - src_copied;
  87
  88        /* Compute merge-score, which is "how much is removed
  89         * from the source material".  The clean-up stage will
  90         * merge the surviving pair together if the score is
  91         * less than the minimum, after rename/copy runs.
  92         */
  93        *merge_score_p = (int)(src_removed * MAX_SCORE / src->size);
  94        if (*merge_score_p > break_score)
  95                return 1;
  96
  97        /* Extent of damage, which counts both inserts and
  98         * deletes.
  99         */
 100        delta_size = src_removed + literal_added;
 101        if (delta_size * MAX_SCORE / max_size < break_score)
 102                return 0;
 103
 104        /* If you removed a lot without adding new material, that is
 105         * not really a rewrite.
 106         */
 107        if ((src->size * break_score < src_removed * MAX_SCORE) &&
 108            (literal_added * 20 < src_removed) &&
 109            (literal_added * 20 < src_copied))
 110                return 0;
 111
 112        return 1;
 113}
 114
 115void diffcore_break(int break_score)
 116{
 117        struct diff_queue_struct *q = &diff_queued_diff;
 118        struct diff_queue_struct outq;
 119
 120        /* When the filepair has this much edit (insert and delete),
 121         * it is first considered to be a rewrite and broken into a
 122         * create and delete filepair.  This is to help breaking a
 123         * file that had too much new stuff added, possibly from
 124         * moving contents from another file, so that rename/copy can
 125         * match it with the other file.
 126         *
 127         * int break_score; we reuse incoming parameter for this.
 128         */
 129
 130        /* After a pair is broken according to break_score and
 131         * subjected to rename/copy, both of them may survive intact,
 132         * due to lack of suitable rename/copy peer.  Or, the caller
 133         * may be calling us without using rename/copy.  When that
 134         * happens, we merge the broken pieces back into one
 135         * modification together if the pair did not have more than
 136         * this much delete.  For this computation, we do not take
 137         * insert into account at all.  If you start from a 100-line
 138         * file and delete 97 lines of it, it does not matter if you
 139         * add 27 lines to it to make a new 30-line file or if you add
 140         * 997 lines to it to make a 1000-line file.  Either way what
 141         * you did was a rewrite of 97%.  On the other hand, if you
 142         * delete 3 lines, keeping 97 lines intact, it does not matter
 143         * if you add 3 lines to it to make a new 100-line file or if
 144         * you add 903 lines to it to make a new 1000-line file.
 145         * Either way you did a lot of additions and not a rewrite.
 146         * This merge happens to catch the latter case.  A merge_score
 147         * of 80% would be a good default value (a broken pair that
 148         * has score lower than merge_score will be merged back
 149         * together).
 150         */
 151        int merge_score;
 152        int i;
 153
 154        /* See comment on DEFAULT_BREAK_SCORE and
 155         * DEFAULT_MERGE_SCORE in diffcore.h
 156         */
 157        merge_score = (break_score >> 16) & 0xFFFF;
 158        break_score = (break_score & 0xFFFF);
 159
 160        if (!break_score)
 161                break_score = DEFAULT_BREAK_SCORE;
 162        if (!merge_score)
 163                merge_score = DEFAULT_MERGE_SCORE;
 164
 165        DIFF_QUEUE_CLEAR(&outq);
 166
 167        for (i = 0; i < q->nr; i++) {
 168                struct diff_filepair *p = q->queue[i];
 169                int score;
 170
 171                /*
 172                 * We deal only with in-place edit of blobs.
 173                 * We do not break anything else.
 174                 */
 175                if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) &&
 176                    object_type(p->one->mode) == OBJ_BLOB &&
 177                    object_type(p->two->mode) == OBJ_BLOB &&
 178                    !strcmp(p->one->path, p->two->path)) {
 179                        if (should_break(p->one, p->two,
 180                                         break_score, &score)) {
 181                                /* Split this into delete and create */
 182                                struct diff_filespec *null_one, *null_two;
 183                                struct diff_filepair *dp;
 184
 185                                /* Set score to 0 for the pair that
 186                                 * needs to be merged back together
 187                                 * should they survive rename/copy.
 188                                 * Also we do not want to break very
 189                                 * small files.
 190                                 */
 191                                if (score < merge_score)
 192                                        score = 0;
 193
 194                                /* deletion of one */
 195                                null_one = alloc_filespec(p->one->path);
 196                                dp = diff_queue(&outq, p->one, null_one);
 197                                dp->score = score;
 198                                dp->broken_pair = 1;
 199
 200                                /* creation of two */
 201                                null_two = alloc_filespec(p->two->path);
 202                                dp = diff_queue(&outq, null_two, p->two);
 203                                dp->score = score;
 204                                dp->broken_pair = 1;
 205
 206                                diff_free_filespec_blob(p->one);
 207                                diff_free_filespec_blob(p->two);
 208                                free(p); /* not diff_free_filepair(), we are
 209                                          * reusing one and two here.
 210                                          */
 211                                continue;
 212                        }
 213                }
 214                diff_free_filespec_data(p->one);
 215                diff_free_filespec_data(p->two);
 216                diff_q(&outq, p);
 217        }
 218        free(q->queue);
 219        *q = outq;
 220
 221        return;
 222}
 223
 224static void merge_broken(struct diff_filepair *p,
 225                         struct diff_filepair *pp,
 226                         struct diff_queue_struct *outq)
 227{
 228        /* p and pp are broken pairs we want to merge */
 229        struct diff_filepair *c = p, *d = pp, *dp;
 230        if (DIFF_FILE_VALID(p->one)) {
 231                /* this must be a delete half */
 232                d = p; c = pp;
 233        }
 234        /* Sanity check */
 235        if (!DIFF_FILE_VALID(d->one))
 236                die("internal error in merge #1");
 237        if (DIFF_FILE_VALID(d->two))
 238                die("internal error in merge #2");
 239        if (DIFF_FILE_VALID(c->one))
 240                die("internal error in merge #3");
 241        if (!DIFF_FILE_VALID(c->two))
 242                die("internal error in merge #4");
 243
 244        dp = diff_queue(outq, d->one, c->two);
 245        dp->score = p->score;
 246        diff_free_filespec_data(d->two);
 247        diff_free_filespec_data(c->one);
 248        free(d);
 249        free(c);
 250}
 251
 252void diffcore_merge_broken(void)
 253{
 254        struct diff_queue_struct *q = &diff_queued_diff;
 255        struct diff_queue_struct outq;
 256        int i, j;
 257
 258        DIFF_QUEUE_CLEAR(&outq);
 259
 260        for (i = 0; i < q->nr; i++) {
 261                struct diff_filepair *p = q->queue[i];
 262                if (!p)
 263                        /* we already merged this with its peer */
 264                        continue;
 265                else if (p->broken_pair &&
 266                         !strcmp(p->one->path, p->two->path)) {
 267                        /* If the peer also survived rename/copy, then
 268                         * we merge them back together.
 269                         */
 270                        for (j = i + 1; j < q->nr; j++) {
 271                                struct diff_filepair *pp = q->queue[j];
 272                                if (pp->broken_pair &&
 273                                    !strcmp(pp->one->path, pp->two->path) &&
 274                                    !strcmp(p->one->path, pp->two->path)) {
 275                                        /* Peer survived.  Merge them */
 276                                        merge_broken(p, pp, &outq);
 277                                        q->queue[j] = NULL;
 278                                        break;
 279                                }
 280                        }
 281                        if (q->nr <= j)
 282                                /* The peer did not survive, so we keep
 283                                 * it in the output.
 284                                 */
 285                                diff_q(&outq, p);
 286                }
 287                else
 288                        diff_q(&outq, p);
 289        }
 290        free(q->queue);
 291        *q = outq;
 292
 293        return;
 294}