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 (!src->size) 72 return 0; /* we do not let empty files get renamed */ 73 74 if (diffcore_count_changes(src, dst, 75 &src->cnt_data, &dst->cnt_data, 76 0, 77 &src_copied, &literal_added)) 78 return 0; 79 80 /* sanity */ 81 if (src->size < src_copied) 82 src_copied = src->size; 83 if (dst->size < literal_added + src_copied) { 84 if (src_copied < dst->size) 85 literal_added = dst->size - src_copied; 86 else 87 literal_added = 0; 88 } 89 src_removed = src->size - src_copied; 90 91 /* Compute merge-score, which is "how much is removed 92 * from the source material". The clean-up stage will 93 * merge the surviving pair together if the score is 94 * less than the minimum, after rename/copy runs. 95 */ 96 *merge_score_p = (int)(src_removed * MAX_SCORE / src->size); 97 if (*merge_score_p > break_score) 98 return 1; 99 100 /* Extent of damage, which counts both inserts and 101 * deletes. 102 */ 103 delta_size = src_removed + literal_added; 104 if (delta_size * MAX_SCORE / max_size < break_score) 105 return 0; 106 107 /* If you removed a lot without adding new material, that is 108 * not really a rewrite. 109 */ 110 if ((src->size * break_score < src_removed * MAX_SCORE) && 111 (literal_added * 20 < src_removed) && 112 (literal_added * 20 < src_copied)) 113 return 0; 114 115 return 1; 116} 117 118void diffcore_break(int break_score) 119{ 120 struct diff_queue_struct *q = &diff_queued_diff; 121 struct diff_queue_struct outq; 122 123 /* When the filepair has this much edit (insert and delete), 124 * it is first considered to be a rewrite and broken into a 125 * create and delete filepair. This is to help breaking a 126 * file that had too much new stuff added, possibly from 127 * moving contents from another file, so that rename/copy can 128 * match it with the other file. 129 * 130 * int break_score; we reuse incoming parameter for this. 131 */ 132 133 /* After a pair is broken according to break_score and 134 * subjected to rename/copy, both of them may survive intact, 135 * due to lack of suitable rename/copy peer. Or, the caller 136 * may be calling us without using rename/copy. When that 137 * happens, we merge the broken pieces back into one 138 * modification together if the pair did not have more than 139 * this much delete. For this computation, we do not take 140 * insert into account at all. If you start from a 100-line 141 * file and delete 97 lines of it, it does not matter if you 142 * add 27 lines to it to make a new 30-line file or if you add 143 * 997 lines to it to make a 1000-line file. Either way what 144 * you did was a rewrite of 97%. On the other hand, if you 145 * delete 3 lines, keeping 97 lines intact, it does not matter 146 * if you add 3 lines to it to make a new 100-line file or if 147 * you add 903 lines to it to make a new 1000-line file. 148 * Either way you did a lot of additions and not a rewrite. 149 * This merge happens to catch the latter case. A merge_score 150 * of 80% would be a good default value (a broken pair that 151 * has score lower than merge_score will be merged back 152 * together). 153 */ 154 int merge_score; 155 int i; 156 157 /* See comment on DEFAULT_BREAK_SCORE and 158 * DEFAULT_MERGE_SCORE in diffcore.h 159 */ 160 merge_score = (break_score >> 16) & 0xFFFF; 161 break_score = (break_score & 0xFFFF); 162 163 if (!break_score) 164 break_score = DEFAULT_BREAK_SCORE; 165 if (!merge_score) 166 merge_score = DEFAULT_MERGE_SCORE; 167 168 DIFF_QUEUE_CLEAR(&outq); 169 170 for (i = 0; i < q->nr; i++) { 171 struct diff_filepair *p = q->queue[i]; 172 int score; 173 174 /* 175 * We deal only with in-place edit of blobs. 176 * We do not break anything else. 177 */ 178 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 179 object_type(p->one->mode) == OBJ_BLOB && 180 object_type(p->two->mode) == OBJ_BLOB && 181 !strcmp(p->one->path, p->two->path)) { 182 if (should_break(p->one, p->two, 183 break_score, &score)) { 184 /* Split this into delete and create */ 185 struct diff_filespec *null_one, *null_two; 186 struct diff_filepair *dp; 187 188 /* Set score to 0 for the pair that 189 * needs to be merged back together 190 * should they survive rename/copy. 191 * Also we do not want to break very 192 * small files. 193 */ 194 if (score < merge_score) 195 score = 0; 196 197 /* deletion of one */ 198 null_one = alloc_filespec(p->one->path); 199 dp = diff_queue(&outq, p->one, null_one); 200 dp->score = score; 201 dp->broken_pair = 1; 202 203 /* creation of two */ 204 null_two = alloc_filespec(p->two->path); 205 dp = diff_queue(&outq, null_two, p->two); 206 dp->score = score; 207 dp->broken_pair = 1; 208 209 diff_free_filespec_blob(p->one); 210 diff_free_filespec_blob(p->two); 211 free(p); /* not diff_free_filepair(), we are 212 * reusing one and two here. 213 */ 214 continue; 215 } 216 } 217 diff_free_filespec_data(p->one); 218 diff_free_filespec_data(p->two); 219 diff_q(&outq, p); 220 } 221 free(q->queue); 222 *q = outq; 223 224 return; 225} 226 227static void merge_broken(struct diff_filepair *p, 228 struct diff_filepair *pp, 229 struct diff_queue_struct *outq) 230{ 231 /* p and pp are broken pairs we want to merge */ 232 struct diff_filepair *c = p, *d = pp, *dp; 233 if (DIFF_FILE_VALID(p->one)) { 234 /* this must be a delete half */ 235 d = p; c = pp; 236 } 237 /* Sanity check */ 238 if (!DIFF_FILE_VALID(d->one)) 239 die("internal error in merge #1"); 240 if (DIFF_FILE_VALID(d->two)) 241 die("internal error in merge #2"); 242 if (DIFF_FILE_VALID(c->one)) 243 die("internal error in merge #3"); 244 if (!DIFF_FILE_VALID(c->two)) 245 die("internal error in merge #4"); 246 247 dp = diff_queue(outq, d->one, c->two); 248 dp->score = p->score; 249 diff_free_filespec_data(d->two); 250 diff_free_filespec_data(c->one); 251 free(d); 252 free(c); 253} 254 255void diffcore_merge_broken(void) 256{ 257 struct diff_queue_struct *q = &diff_queued_diff; 258 struct diff_queue_struct outq; 259 int i, j; 260 261 DIFF_QUEUE_CLEAR(&outq); 262 263 for (i = 0; i < q->nr; i++) { 264 struct diff_filepair *p = q->queue[i]; 265 if (!p) 266 /* we already merged this with its peer */ 267 continue; 268 else if (p->broken_pair && 269 !strcmp(p->one->path, p->two->path)) { 270 /* If the peer also survived rename/copy, then 271 * we merge them back together. 272 */ 273 for (j = i + 1; j < q->nr; j++) { 274 struct diff_filepair *pp = q->queue[j]; 275 if (pp->broken_pair && 276 !strcmp(pp->one->path, pp->two->path) && 277 !strcmp(p->one->path, pp->two->path)) { 278 /* Peer survived. Merge them */ 279 merge_broken(p, pp, &outq); 280 q->queue[j] = NULL; 281 break; 282 } 283 } 284 if (q->nr <= j) 285 /* The peer did not survive, so we keep 286 * it in the output. 287 */ 288 diff_q(&outq, p); 289 } 290 else 291 diff_q(&outq, p); 292 } 293 free(q->queue); 294 *q = outq; 295 296 return; 297}