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 int to_break = 0; 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 /* Compute merge-score, which is "how much is removed 76 * from the source material". The clean-up stage will 77 * merge the surviving pair together if the score is 78 * less than the minimum, after rename/copy runs. 79 */ 80 if (src->size <= src_copied) 81 ; /* all copied, nothing removed */ 82 else { 83 delta_size = src->size - src_copied; 84 *merge_score_p = delta_size * MAX_SCORE / src->size; 85 } 86 87 /* Extent of damage, which counts both inserts and 88 * deletes. 89 */ 90 if (src->size + literal_added <= src_copied) 91 delta_size = 0; /* avoid wrapping around */ 92 else 93 delta_size = (src->size - src_copied) + literal_added; 94 95 /* We break if the edit exceeds the minimum. 96 * i.e. (break_score / MAX_SCORE < delta_size / base_size) 97 */ 98 if (break_score * base_size < delta_size * MAX_SCORE) 99 to_break = 1; 100 101 return to_break; 102} 103 104void diffcore_break(int break_score) 105{ 106 struct diff_queue_struct *q = &diff_queued_diff; 107 struct diff_queue_struct outq; 108 109 /* When the filepair has this much edit (insert and delete), 110 * it is first considered to be a rewrite and broken into a 111 * create and delete filepair. This is to help breaking a 112 * file that had too much new stuff added, possibly from 113 * moving contents from another file, so that rename/copy can 114 * match it with the other file. 115 * 116 * int break_score; we reuse incoming parameter for this. 117 */ 118 119 /* After a pair is broken according to break_score and 120 * subjected to rename/copy, both of them may survive intact, 121 * due to lack of suitable rename/copy peer. Or, the caller 122 * may be calling us without using rename/copy. When that 123 * happens, we merge the broken pieces back into one 124 * modification together if the pair did not have more than 125 * this much delete. For this computation, we do not take 126 * insert into account at all. If you start from a 100-line 127 * file and delete 97 lines of it, it does not matter if you 128 * add 27 lines to it to make a new 30-line file or if you add 129 * 997 lines to it to make a 1000-line file. Either way what 130 * you did was a rewrite of 97%. On the other hand, if you 131 * delete 3 lines, keeping 97 lines intact, it does not matter 132 * if you add 3 lines to it to make a new 100-line file or if 133 * you add 903 lines to it to make a new 1000-line file. 134 * Either way you did a lot of additions and not a rewrite. 135 * This merge happens to catch the latter case. A merge_score 136 * of 80% would be a good default value (a broken pair that 137 * has score lower than merge_score will be merged back 138 * together). 139 */ 140 int merge_score; 141 int i; 142 143 /* See comment on DEFAULT_BREAK_SCORE and 144 * DEFAULT_MERGE_SCORE in diffcore.h 145 */ 146 merge_score = (break_score >> 16) & 0xFFFF; 147 break_score = (break_score & 0xFFFF); 148 149 if (!break_score) 150 break_score = DEFAULT_BREAK_SCORE; 151 if (!merge_score) 152 merge_score = DEFAULT_MERGE_SCORE; 153 154 outq.nr = outq.alloc = 0; 155 outq.queue = NULL; 156 157 for (i = 0; i < q->nr; i++) { 158 struct diff_filepair *p = q->queue[i]; 159 int score; 160 161 /* We deal only with in-place edit of non directory. 162 * We do not break anything else. 163 */ 164 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 165 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) && 166 !strcmp(p->one->path, p->two->path)) { 167 if (should_break(p->one, p->two, 168 break_score, &score)) { 169 /* Split this into delete and create */ 170 struct diff_filespec *null_one, *null_two; 171 struct diff_filepair *dp; 172 173 /* Set score to 0 for the pair that 174 * needs to be merged back together 175 * should they survive rename/copy. 176 * Also we do not want to break very 177 * small files. 178 */ 179 if (score < merge_score) 180 score = 0; 181 182 /* deletion of one */ 183 null_one = alloc_filespec(p->one->path); 184 dp = diff_queue(&outq, p->one, null_one); 185 dp->score = score; 186 dp->broken_pair = 1; 187 188 /* creation of two */ 189 null_two = alloc_filespec(p->two->path); 190 dp = diff_queue(&outq, null_two, p->two); 191 dp->score = score; 192 dp->broken_pair = 1; 193 194 free(p); /* not diff_free_filepair(), we are 195 * reusing one and two here. 196 */ 197 continue; 198 } 199 } 200 diff_q(&outq, p); 201 } 202 free(q->queue); 203 *q = outq; 204 205 return; 206} 207 208static void merge_broken(struct diff_filepair *p, 209 struct diff_filepair *pp, 210 struct diff_queue_struct *outq) 211{ 212 /* p and pp are broken pairs we want to merge */ 213 struct diff_filepair *c = p, *d = pp, *dp; 214 if (DIFF_FILE_VALID(p->one)) { 215 /* this must be a delete half */ 216 d = p; c = pp; 217 } 218 /* Sanity check */ 219 if (!DIFF_FILE_VALID(d->one)) 220 die("internal error in merge #1"); 221 if (DIFF_FILE_VALID(d->two)) 222 die("internal error in merge #2"); 223 if (DIFF_FILE_VALID(c->one)) 224 die("internal error in merge #3"); 225 if (!DIFF_FILE_VALID(c->two)) 226 die("internal error in merge #4"); 227 228 dp = diff_queue(outq, d->one, c->two); 229 dp->score = p->score; 230 diff_free_filespec_data(d->two); 231 diff_free_filespec_data(c->one); 232 free(d); 233 free(c); 234} 235 236void diffcore_merge_broken(void) 237{ 238 struct diff_queue_struct *q = &diff_queued_diff; 239 struct diff_queue_struct outq; 240 int i, j; 241 242 outq.nr = outq.alloc = 0; 243 outq.queue = NULL; 244 245 for (i = 0; i < q->nr; i++) { 246 struct diff_filepair *p = q->queue[i]; 247 if (!p) 248 /* we already merged this with its peer */ 249 continue; 250 else if (p->broken_pair && 251 !strcmp(p->one->path, p->two->path)) { 252 /* If the peer also survived rename/copy, then 253 * we merge them back together. 254 */ 255 for (j = i + 1; j < q->nr; j++) { 256 struct diff_filepair *pp = q->queue[j]; 257 if (pp->broken_pair && 258 !strcmp(pp->one->path, pp->two->path) && 259 !strcmp(p->one->path, pp->two->path)) { 260 /* Peer survived. Merge them */ 261 merge_broken(p, pp, &outq); 262 q->queue[j] = NULL; 263 break; 264 } 265 } 266 if (q->nr <= j) 267 /* The peer did not survive, so we keep 268 * it in the output. 269 */ 270 diff_q(&outq, p); 271 } 272 else 273 diff_q(&outq, p); 274 } 275 free(q->queue); 276 *q = outq; 277 278 return; 279}