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}