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, src_copied, literal_added, 49 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 !memcmp(src->sha1, dst->sha1, 20)) 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 if (base_size < MINIMUM_BREAK_SIZE) 67 return 0; /* we do not break too small filepair */ 68 69 if (diffcore_count_changes(src->data, src->size, 70 dst->data, dst->size, 71 0, 72 &src_copied, &literal_added)) 73 return 0; 74 75 /* sanity */ 76 if (src->size < src_copied) 77 src_copied = src->size; 78 if (dst->size < literal_added + src_copied) { 79 if (src_copied < dst->size) 80 literal_added = dst->size - src_copied; 81 else 82 literal_added = 0; 83 } 84 src_removed = src->size - src_copied; 85 86 /* Compute merge-score, which is "how much is removed 87 * from the source material". The clean-up stage will 88 * merge the surviving pair together if the score is 89 * less than the minimum, after rename/copy runs. 90 */ 91 *merge_score_p = src_removed * MAX_SCORE / src->size; 92 93 /* Extent of damage, which counts both inserts and 94 * deletes. 95 */ 96 delta_size = src_removed + literal_added; 97 if (delta_size * MAX_SCORE / base_size < break_score) 98 return 0; 99 100 /* If you removed a lot without adding new material, that is 101 * not really a rewrite. 102 */ 103 if ((src->size * break_score < src_removed * MAX_SCORE) && 104 (literal_added * 20 < src_removed) && 105 (literal_added * 20 < src_copied)) 106 return 0; 107 108 return 1; 109} 110 111void diffcore_break(int break_score) 112{ 113 struct diff_queue_struct *q = &diff_queued_diff; 114 struct diff_queue_struct outq; 115 116 /* When the filepair has this much edit (insert and delete), 117 * it is first considered to be a rewrite and broken into a 118 * create and delete filepair. This is to help breaking a 119 * file that had too much new stuff added, possibly from 120 * moving contents from another file, so that rename/copy can 121 * match it with the other file. 122 * 123 * int break_score; we reuse incoming parameter for this. 124 */ 125 126 /* After a pair is broken according to break_score and 127 * subjected to rename/copy, both of them may survive intact, 128 * due to lack of suitable rename/copy peer. Or, the caller 129 * may be calling us without using rename/copy. When that 130 * happens, we merge the broken pieces back into one 131 * modification together if the pair did not have more than 132 * this much delete. For this computation, we do not take 133 * insert into account at all. If you start from a 100-line 134 * file and delete 97 lines of it, it does not matter if you 135 * add 27 lines to it to make a new 30-line file or if you add 136 * 997 lines to it to make a 1000-line file. Either way what 137 * you did was a rewrite of 97%. On the other hand, if you 138 * delete 3 lines, keeping 97 lines intact, it does not matter 139 * if you add 3 lines to it to make a new 100-line file or if 140 * you add 903 lines to it to make a new 1000-line file. 141 * Either way you did a lot of additions and not a rewrite. 142 * This merge happens to catch the latter case. A merge_score 143 * of 80% would be a good default value (a broken pair that 144 * has score lower than merge_score will be merged back 145 * together). 146 */ 147 int merge_score; 148 int i; 149 150 /* See comment on DEFAULT_BREAK_SCORE and 151 * DEFAULT_MERGE_SCORE in diffcore.h 152 */ 153 merge_score = (break_score >> 16) & 0xFFFF; 154 break_score = (break_score & 0xFFFF); 155 156 if (!break_score) 157 break_score = DEFAULT_BREAK_SCORE; 158 if (!merge_score) 159 merge_score = DEFAULT_MERGE_SCORE; 160 161 outq.nr = outq.alloc = 0; 162 outq.queue = NULL; 163 164 for (i = 0; i < q->nr; i++) { 165 struct diff_filepair *p = q->queue[i]; 166 int score; 167 168 /* We deal only with in-place edit of non directory. 169 * We do not break anything else. 170 */ 171 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 172 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) && 173 !strcmp(p->one->path, p->two->path)) { 174 if (should_break(p->one, p->two, 175 break_score, &score)) { 176 /* Split this into delete and create */ 177 struct diff_filespec *null_one, *null_two; 178 struct diff_filepair *dp; 179 180 /* Set score to 0 for the pair that 181 * needs to be merged back together 182 * should they survive rename/copy. 183 * Also we do not want to break very 184 * small files. 185 */ 186 if (score < merge_score) 187 score = 0; 188 189 /* deletion of one */ 190 null_one = alloc_filespec(p->one->path); 191 dp = diff_queue(&outq, p->one, null_one); 192 dp->score = score; 193 dp->broken_pair = 1; 194 195 /* creation of two */ 196 null_two = alloc_filespec(p->two->path); 197 dp = diff_queue(&outq, null_two, p->two); 198 dp->score = score; 199 dp->broken_pair = 1; 200 201 free(p); /* not diff_free_filepair(), we are 202 * reusing one and two here. 203 */ 204 continue; 205 } 206 } 207 diff_q(&outq, p); 208 } 209 free(q->queue); 210 *q = outq; 211 212 return; 213} 214 215static void merge_broken(struct diff_filepair *p, 216 struct diff_filepair *pp, 217 struct diff_queue_struct *outq) 218{ 219 /* p and pp are broken pairs we want to merge */ 220 struct diff_filepair *c = p, *d = pp, *dp; 221 if (DIFF_FILE_VALID(p->one)) { 222 /* this must be a delete half */ 223 d = p; c = pp; 224 } 225 /* Sanity check */ 226 if (!DIFF_FILE_VALID(d->one)) 227 die("internal error in merge #1"); 228 if (DIFF_FILE_VALID(d->two)) 229 die("internal error in merge #2"); 230 if (DIFF_FILE_VALID(c->one)) 231 die("internal error in merge #3"); 232 if (!DIFF_FILE_VALID(c->two)) 233 die("internal error in merge #4"); 234 235 dp = diff_queue(outq, d->one, c->two); 236 dp->score = p->score; 237 diff_free_filespec_data(d->two); 238 diff_free_filespec_data(c->one); 239 free(d); 240 free(c); 241} 242 243void diffcore_merge_broken(void) 244{ 245 struct diff_queue_struct *q = &diff_queued_diff; 246 struct diff_queue_struct outq; 247 int i, j; 248 249 outq.nr = outq.alloc = 0; 250 outq.queue = NULL; 251 252 for (i = 0; i < q->nr; i++) { 253 struct diff_filepair *p = q->queue[i]; 254 if (!p) 255 /* we already merged this with its peer */ 256 continue; 257 else if (p->broken_pair && 258 !strcmp(p->one->path, p->two->path)) { 259 /* If the peer also survived rename/copy, then 260 * we merge them back together. 261 */ 262 for (j = i + 1; j < q->nr; j++) { 263 struct diff_filepair *pp = q->queue[j]; 264 if (pp->broken_pair && 265 !strcmp(pp->one->path, pp->two->path) && 266 !strcmp(p->one->path, pp->two->path)) { 267 /* Peer survived. Merge them */ 268 merge_broken(p, pp, &outq); 269 q->queue[j] = NULL; 270 break; 271 } 272 } 273 if (q->nr <= j) 274 /* The peer did not survive, so we keep 275 * it in the output. 276 */ 277 diff_q(&outq, p); 278 } 279 else 280 diff_q(&outq, p); 281 } 282 free(q->queue); 283 *q = outq; 284 285 return; 286}