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 *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 base_size = ((src->size < dst->size) ? src->size : dst->size); 68 max_size = ((src->size > dst->size) ? src->size : dst->size); 69 if (max_size < MINIMUM_BREAK_SIZE) 70 return 0; /* we do not break too small filepair */ 71 72 if (diffcore_count_changes(src, dst, 73 NULL, NULL, 74 0, 75 &src_copied, &literal_added)) 76 return 0; 77 78 /* sanity */ 79 if (src->size < src_copied) 80 src_copied = src->size; 81 if (dst->size < literal_added + src_copied) { 82 if (src_copied < dst->size) 83 literal_added = dst->size - src_copied; 84 else 85 literal_added = 0; 86 } 87 src_removed = src->size - src_copied; 88 89 /* Compute merge-score, which is "how much is removed 90 * from the source material". The clean-up stage will 91 * merge the surviving pair together if the score is 92 * less than the minimum, after rename/copy runs. 93 */ 94 *merge_score_p = (int)(src_removed * MAX_SCORE / src->size); 95 if (*merge_score_p > break_score) 96 return 1; 97 98 /* Extent of damage, which counts both inserts and 99 * deletes. 100 */ 101 delta_size = src_removed + literal_added; 102 if (delta_size * MAX_SCORE / max_size < break_score) 103 return 0; 104 105 /* If you removed a lot without adding new material, that is 106 * not really a rewrite. 107 */ 108 if ((src->size * break_score < src_removed * MAX_SCORE) && 109 (literal_added * 20 < src_removed) && 110 (literal_added * 20 < src_copied)) 111 return 0; 112 113 return 1; 114} 115 116void diffcore_break(int break_score) 117{ 118 struct diff_queue_struct *q = &diff_queued_diff; 119 struct diff_queue_struct outq; 120 121 /* When the filepair has this much edit (insert and delete), 122 * it is first considered to be a rewrite and broken into a 123 * create and delete filepair. This is to help breaking a 124 * file that had too much new stuff added, possibly from 125 * moving contents from another file, so that rename/copy can 126 * match it with the other file. 127 * 128 * int break_score; we reuse incoming parameter for this. 129 */ 130 131 /* After a pair is broken according to break_score and 132 * subjected to rename/copy, both of them may survive intact, 133 * due to lack of suitable rename/copy peer. Or, the caller 134 * may be calling us without using rename/copy. When that 135 * happens, we merge the broken pieces back into one 136 * modification together if the pair did not have more than 137 * this much delete. For this computation, we do not take 138 * insert into account at all. If you start from a 100-line 139 * file and delete 97 lines of it, it does not matter if you 140 * add 27 lines to it to make a new 30-line file or if you add 141 * 997 lines to it to make a 1000-line file. Either way what 142 * you did was a rewrite of 97%. On the other hand, if you 143 * delete 3 lines, keeping 97 lines intact, it does not matter 144 * if you add 3 lines to it to make a new 100-line file or if 145 * you add 903 lines to it to make a new 1000-line file. 146 * Either way you did a lot of additions and not a rewrite. 147 * This merge happens to catch the latter case. A merge_score 148 * of 80% would be a good default value (a broken pair that 149 * has score lower than merge_score will be merged back 150 * together). 151 */ 152 int merge_score; 153 int i; 154 155 /* See comment on DEFAULT_BREAK_SCORE and 156 * DEFAULT_MERGE_SCORE in diffcore.h 157 */ 158 merge_score = (break_score >> 16) & 0xFFFF; 159 break_score = (break_score & 0xFFFF); 160 161 if (!break_score) 162 break_score = DEFAULT_BREAK_SCORE; 163 if (!merge_score) 164 merge_score = DEFAULT_MERGE_SCORE; 165 166 outq.nr = outq.alloc = 0; 167 outq.queue = NULL; 168 169 for (i = 0; i < q->nr; i++) { 170 struct diff_filepair *p = q->queue[i]; 171 int score; 172 173 /* 174 * We deal only with in-place edit of blobs. 175 * We do not break anything else. 176 */ 177 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 178 object_type(p->one->mode) == OBJ_BLOB && 179 object_type(p->two->mode) == OBJ_BLOB && 180 !strcmp(p->one->path, p->two->path)) { 181 if (should_break(p->one, p->two, 182 break_score, &score)) { 183 /* Split this into delete and create */ 184 struct diff_filespec *null_one, *null_two; 185 struct diff_filepair *dp; 186 187 /* Set score to 0 for the pair that 188 * needs to be merged back together 189 * should they survive rename/copy. 190 * Also we do not want to break very 191 * small files. 192 */ 193 if (score < merge_score) 194 score = 0; 195 196 /* deletion of one */ 197 null_one = alloc_filespec(p->one->path); 198 dp = diff_queue(&outq, p->one, null_one); 199 dp->score = score; 200 dp->broken_pair = 1; 201 202 /* creation of two */ 203 null_two = alloc_filespec(p->two->path); 204 dp = diff_queue(&outq, null_two, p->two); 205 dp->score = score; 206 dp->broken_pair = 1; 207 208 free(p); /* not diff_free_filepair(), we are 209 * reusing one and two here. 210 */ 211 continue; 212 } 213 } 214 diff_q(&outq, p); 215 } 216 free(q->queue); 217 *q = outq; 218 219 return; 220} 221 222static void merge_broken(struct diff_filepair *p, 223 struct diff_filepair *pp, 224 struct diff_queue_struct *outq) 225{ 226 /* p and pp are broken pairs we want to merge */ 227 struct diff_filepair *c = p, *d = pp, *dp; 228 if (DIFF_FILE_VALID(p->one)) { 229 /* this must be a delete half */ 230 d = p; c = pp; 231 } 232 /* Sanity check */ 233 if (!DIFF_FILE_VALID(d->one)) 234 die("internal error in merge #1"); 235 if (DIFF_FILE_VALID(d->two)) 236 die("internal error in merge #2"); 237 if (DIFF_FILE_VALID(c->one)) 238 die("internal error in merge #3"); 239 if (!DIFF_FILE_VALID(c->two)) 240 die("internal error in merge #4"); 241 242 dp = diff_queue(outq, d->one, c->two); 243 dp->score = p->score; 244 diff_free_filespec_data(d->two); 245 diff_free_filespec_data(c->one); 246 free(d); 247 free(c); 248} 249 250void diffcore_merge_broken(void) 251{ 252 struct diff_queue_struct *q = &diff_queued_diff; 253 struct diff_queue_struct outq; 254 int i, j; 255 256 outq.nr = outq.alloc = 0; 257 outq.queue = NULL; 258 259 for (i = 0; i < q->nr; i++) { 260 struct diff_filepair *p = q->queue[i]; 261 if (!p) 262 /* we already merged this with its peer */ 263 continue; 264 else if (p->broken_pair && 265 !strcmp(p->one->path, p->two->path)) { 266 /* If the peer also survived rename/copy, then 267 * we merge them back together. 268 */ 269 for (j = i + 1; j < q->nr; j++) { 270 struct diff_filepair *pp = q->queue[j]; 271 if (pp->broken_pair && 272 !strcmp(pp->one->path, pp->two->path) && 273 !strcmp(p->one->path, pp->two->path)) { 274 /* Peer survived. Merge them */ 275 merge_broken(p, pp, &outq); 276 q->queue[j] = NULL; 277 break; 278 } 279 } 280 if (q->nr <= j) 281 /* The peer did not survive, so we keep 282 * it in the output. 283 */ 284 diff_q(&outq, p); 285 } 286 else 287 diff_q(&outq, p); 288 } 289 free(q->queue); 290 *q = outq; 291 292 return; 293}