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, base_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 return 0; /* leave symlink rename alone */ 57 58 if (src->sha1_valid && dst->sha1_valid && 59 !hashcmp(src->sha1, dst->sha1)) 60 return 0; /* they are the same */ 61 62 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0)) 63 return 0; /* error but caught downstream */ 64 65 base_size = ((src->size < dst->size) ? src->size : dst->size); 66 max_size = ((src->size > dst->size) ? src->size : dst->size); 67 if (max_size < MINIMUM_BREAK_SIZE) 68 return 0; /* we do not break too small filepair */ 69 70 if (diffcore_count_changes(src, dst, 71 NULL, NULL, 72 0, 73 &src_copied, &literal_added)) 74 return 0; 75 76 /* sanity */ 77 if (src->size < src_copied) 78 src_copied = src->size; 79 if (dst->size < literal_added + src_copied) { 80 if (src_copied < dst->size) 81 literal_added = dst->size - src_copied; 82 else 83 literal_added = 0; 84 } 85 src_removed = src->size - src_copied; 86 87 /* Compute merge-score, which is "how much is removed 88 * from the source material". The clean-up stage will 89 * merge the surviving pair together if the score is 90 * less than the minimum, after rename/copy runs. 91 */ 92 *merge_score_p = (int)(src_removed * MAX_SCORE / src->size); 93 if (*merge_score_p > break_score) 94 return 1; 95 96 /* Extent of damage, which counts both inserts and 97 * deletes. 98 */ 99 delta_size = src_removed + literal_added; 100 if (delta_size * MAX_SCORE / max_size < break_score) 101 return 0; 102 103 /* If you removed a lot without adding new material, that is 104 * not really a rewrite. 105 */ 106 if ((src->size * break_score < src_removed * MAX_SCORE) && 107 (literal_added * 20 < src_removed) && 108 (literal_added * 20 < src_copied)) 109 return 0; 110 111 return 1; 112} 113 114void diffcore_break(int break_score) 115{ 116 struct diff_queue_struct *q = &diff_queued_diff; 117 struct diff_queue_struct outq; 118 119 /* When the filepair has this much edit (insert and delete), 120 * it is first considered to be a rewrite and broken into a 121 * create and delete filepair. This is to help breaking a 122 * file that had too much new stuff added, possibly from 123 * moving contents from another file, so that rename/copy can 124 * match it with the other file. 125 * 126 * int break_score; we reuse incoming parameter for this. 127 */ 128 129 /* After a pair is broken according to break_score and 130 * subjected to rename/copy, both of them may survive intact, 131 * due to lack of suitable rename/copy peer. Or, the caller 132 * may be calling us without using rename/copy. When that 133 * happens, we merge the broken pieces back into one 134 * modification together if the pair did not have more than 135 * this much delete. For this computation, we do not take 136 * insert into account at all. If you start from a 100-line 137 * file and delete 97 lines of it, it does not matter if you 138 * add 27 lines to it to make a new 30-line file or if you add 139 * 997 lines to it to make a 1000-line file. Either way what 140 * you did was a rewrite of 97%. On the other hand, if you 141 * delete 3 lines, keeping 97 lines intact, it does not matter 142 * if you add 3 lines to it to make a new 100-line file or if 143 * you add 903 lines to it to make a new 1000-line file. 144 * Either way you did a lot of additions and not a rewrite. 145 * This merge happens to catch the latter case. A merge_score 146 * of 80% would be a good default value (a broken pair that 147 * has score lower than merge_score will be merged back 148 * together). 149 */ 150 int merge_score; 151 int i; 152 153 /* See comment on DEFAULT_BREAK_SCORE and 154 * DEFAULT_MERGE_SCORE in diffcore.h 155 */ 156 merge_score = (break_score >> 16) & 0xFFFF; 157 break_score = (break_score & 0xFFFF); 158 159 if (!break_score) 160 break_score = DEFAULT_BREAK_SCORE; 161 if (!merge_score) 162 merge_score = DEFAULT_MERGE_SCORE; 163 164 outq.nr = outq.alloc = 0; 165 outq.queue = NULL; 166 167 for (i = 0; i < q->nr; i++) { 168 struct diff_filepair *p = q->queue[i]; 169 int score; 170 171 /* We deal only with in-place edit of non directory. 172 * We do not break anything else. 173 */ 174 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 175 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) && 176 !strcmp(p->one->path, p->two->path)) { 177 if (should_break(p->one, p->two, 178 break_score, &score)) { 179 /* Split this into delete and create */ 180 struct diff_filespec *null_one, *null_two; 181 struct diff_filepair *dp; 182 183 /* Set score to 0 for the pair that 184 * needs to be merged back together 185 * should they survive rename/copy. 186 * Also we do not want to break very 187 * small files. 188 */ 189 if (score < merge_score) 190 score = 0; 191 192 /* deletion of one */ 193 null_one = alloc_filespec(p->one->path); 194 dp = diff_queue(&outq, p->one, null_one); 195 dp->score = score; 196 dp->broken_pair = 1; 197 198 /* creation of two */ 199 null_two = alloc_filespec(p->two->path); 200 dp = diff_queue(&outq, null_two, p->two); 201 dp->score = score; 202 dp->broken_pair = 1; 203 204 free(p); /* not diff_free_filepair(), we are 205 * reusing one and two here. 206 */ 207 continue; 208 } 209 } 210 diff_q(&outq, p); 211 } 212 free(q->queue); 213 *q = outq; 214 215 return; 216} 217 218static void merge_broken(struct diff_filepair *p, 219 struct diff_filepair *pp, 220 struct diff_queue_struct *outq) 221{ 222 /* p and pp are broken pairs we want to merge */ 223 struct diff_filepair *c = p, *d = pp, *dp; 224 if (DIFF_FILE_VALID(p->one)) { 225 /* this must be a delete half */ 226 d = p; c = pp; 227 } 228 /* Sanity check */ 229 if (!DIFF_FILE_VALID(d->one)) 230 die("internal error in merge #1"); 231 if (DIFF_FILE_VALID(d->two)) 232 die("internal error in merge #2"); 233 if (DIFF_FILE_VALID(c->one)) 234 die("internal error in merge #3"); 235 if (!DIFF_FILE_VALID(c->two)) 236 die("internal error in merge #4"); 237 238 dp = diff_queue(outq, d->one, c->two); 239 dp->score = p->score; 240 diff_free_filespec_data(d->two); 241 diff_free_filespec_data(c->one); 242 free(d); 243 free(c); 244} 245 246void diffcore_merge_broken(void) 247{ 248 struct diff_queue_struct *q = &diff_queued_diff; 249 struct diff_queue_struct outq; 250 int i, j; 251 252 outq.nr = outq.alloc = 0; 253 outq.queue = NULL; 254 255 for (i = 0; i < q->nr; i++) { 256 struct diff_filepair *p = q->queue[i]; 257 if (!p) 258 /* we already merged this with its peer */ 259 continue; 260 else if (p->broken_pair && 261 !strcmp(p->one->path, p->two->path)) { 262 /* If the peer also survived rename/copy, then 263 * we merge them back together. 264 */ 265 for (j = i + 1; j < q->nr; j++) { 266 struct diff_filepair *pp = q->queue[j]; 267 if (pp->broken_pair && 268 !strcmp(pp->one->path, pp->two->path) && 269 !strcmp(p->one->path, pp->two->path)) { 270 /* Peer survived. Merge them */ 271 merge_broken(p, pp, &outq); 272 q->queue[j] = NULL; 273 break; 274 } 275 } 276 if (q->nr <= j) 277 /* The peer did not survive, so we keep 278 * it in the output. 279 */ 280 diff_q(&outq, p); 281 } 282 else 283 diff_q(&outq, p); 284 } 285 free(q->queue); 286 *q = outq; 287 288 return; 289}