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