1/* 2 * Copyright (C) 2005 Junio C Hamano 3 */ 4#include "cache.h" 5#include "diff.h" 6#include "diffcore.h" 7#include "delta.h" 8#include "count-delta.h" 9 10static int should_break(struct diff_filespec *src, 11 struct diff_filespec *dst, 12 int break_score, 13 int *merge_score_p) 14{ 15 /* dst is recorded as a modification of src. Are they so 16 * different that we are better off recording this as a pair 17 * of delete and create? 18 * 19 * There are two criteria used in this algorithm. For the 20 * purposes of helping later rename/copy, we take both delete 21 * and insert into account and estimate the amount of "edit". 22 * If the edit is very large, we break this pair so that 23 * rename/copy can pick the pieces up to match with other 24 * files. 25 * 26 * On the other hand, we would want to ignore inserts for the 27 * pure "complete rewrite" detection. As long as most of the 28 * existing contents were removed from the file, it is a 29 * complete rewrite, and if sizable chunk from the original 30 * still remains in the result, it is not a rewrite. It does 31 * not matter how much or how little new material is added to 32 * the file. 33 * 34 * The score we leave for such a broken filepair uses the 35 * latter definition so that later clean-up stage can find the 36 * pieces that should not have been broken according to the 37 * latter definition after rename/copy runs, and merge the 38 * broken pair that have a score lower than given criteria 39 * back together. The break operation itself happens 40 * according to the former definition. 41 * 42 * The minimum_edit parameter tells us when to break (the 43 * amount of "edit" required for us to consider breaking the 44 * pair). We leave the amount of deletion in *merge_score_p 45 * when we return. 46 * 47 * The value we return is 1 if we want the pair to be broken, 48 * or 0 if we do not. 49 */ 50 void *delta; 51 unsigned long delta_size, base_size, src_copied, literal_added; 52 int to_break = 0; 53 54 *merge_score_p = 0; /* assume no deletion --- "do not break" 55 * is the default. 56 */ 57 58 if (!S_ISREG(src->mode) || !S_ISREG(dst->mode)) 59 return 0; /* leave symlink rename alone */ 60 61 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0)) 62 return 0; /* error but caught downstream */ 63 64 delta_size = ((src->size < dst->size) ? 65 (dst->size - src->size) : (src->size - dst->size)); 66 67 /* Notice that we use max of src and dst as the base size, 68 * unlike rename similarity detection. This is so that we do 69 * not mistake a large addition as a complete rewrite. 70 */ 71 base_size = ((src->size < dst->size) ? dst->size : src->size); 72 73 delta = diff_delta(src->data, src->size, 74 dst->data, dst->size, 75 &delta_size); 76 77 /* Estimate the edit size by interpreting delta. */ 78 if (count_delta(delta, delta_size, 79 &src_copied, &literal_added)) { 80 free(delta); 81 return 0; /* we cannot tell */ 82 } 83 free(delta); 84 85 /* Compute merge-score, which is "how much is removed 86 * from the source material". The clean-up stage will 87 * merge the surviving pair together if the score is 88 * less than the minimum, after rename/copy runs. 89 */ 90 if (src->size <= src_copied) 91 delta_size = 0; /* avoid wrapping around */ 92 else 93 delta_size = src->size - src_copied; 94 *merge_score_p = delta_size * MAX_SCORE / src->size; 95 96 /* Extent of damage, which counts both inserts and 97 * deletes. 98 */ 99 if (src->size + literal_added <= src_copied) 100 delta_size = 0; /* avoid wrapping around */ 101 else 102 delta_size = (src->size - src_copied) + literal_added; 103 104 /* We break if the edit exceeds the minimum. 105 * i.e. (break_score / MAX_SCORE < delta_size / base_size) 106 */ 107 if (break_score * base_size < delta_size * MAX_SCORE) 108 to_break = 1; 109 110 return to_break; 111} 112 113void diffcore_break(int break_score) 114{ 115 struct diff_queue_struct *q = &diff_queued_diff; 116 struct diff_queue_struct outq; 117 118 /* When the filepair has this much edit (insert and delete), 119 * it is first considered to be a rewrite and broken into a 120 * create and delete filepair. This is to help breaking a 121 * file that had too much new stuff added, possibly from 122 * moving contents from another file, so that rename/copy can 123 * match it with the other file. 124 * 125 * int break_score; we reuse incoming parameter for this. 126 */ 127 128 /* After a pair is broken according to break_score and 129 * subjected to rename/copy, both of them may survive intact, 130 * due to lack of suitable rename/copy peer. Or, the caller 131 * may be calling us without using rename/copy. When that 132 * happens, we merge the broken pieces back into one 133 * modification together if the pair did not have more than 134 * this much delete. For this computation, we do not take 135 * insert into account at all. If you start from a 100-line 136 * file and delete 97 lines of it, it does not matter if you 137 * add 27 lines to it to make a new 30-line file or if you add 138 * 997 lines to it to make a 1000-line file. Either way what 139 * you did was a rewrite of 97%. On the other hand, if you 140 * delete 3 lines, keeping 97 lines intact, it does not matter 141 * if you add 3 lines to it to make a new 100-line file or if 142 * you add 903 lines to it to make a new 1000-line file. 143 * Either way you did a lot of additions and not a rewrite. 144 * This merge happens to catch the latter case. A merge_score 145 * of 80% would be a good default value (a broken pair that 146 * has score lower than merge_score will be merged back 147 * together). 148 */ 149 int merge_score; 150 int i; 151 152 /* See comment on DEFAULT_BREAK_SCORE and 153 * DEFAULT_MERGE_SCORE in diffcore.h 154 */ 155 merge_score = (break_score >> 16) & 0xFFFF; 156 break_score = (break_score & 0xFFFF); 157 158 if (!break_score) 159 break_score = DEFAULT_BREAK_SCORE; 160 if (!merge_score) 161 merge_score = DEFAULT_MERGE_SCORE; 162 163 outq.nr = outq.alloc = 0; 164 outq.queue = NULL; 165 166 for (i = 0; i < q->nr; i++) { 167 struct diff_filepair *p = q->queue[i]; 168 int score; 169 170 /* We deal only with in-place edit of non directory. 171 * We do not break anything else. 172 */ 173 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 174 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) && 175 !strcmp(p->one->path, p->two->path)) { 176 if (should_break(p->one, p->two, 177 break_score, &score)) { 178 /* Split this into delete and create */ 179 struct diff_filespec *null_one, *null_two; 180 struct diff_filepair *dp; 181 182 /* Set score to 0 for the pair that 183 * needs to be merged back together 184 * should they survive rename/copy. 185 * Also we do not want to break very 186 * small files. 187 */ 188 if ((score < merge_score) || 189 (p->one->size < MINIMUM_BREAK_SIZE)) 190 score = 0; 191 192 /* deletion of one */ 193 null_one = alloc_filespec(p->one->path); 194 dp = diff_queue(&outq, p->one, null_one); 195 dp->score = score; 196 dp->broken_pair = 1; 197 198 /* creation of two */ 199 null_two = alloc_filespec(p->two->path); 200 dp = diff_queue(&outq, null_two, p->two); 201 dp->score = score; 202 dp->broken_pair = 1; 203 204 free(p); /* not diff_free_filepair(), we are 205 * reusing one and two here. 206 */ 207 continue; 208 } 209 } 210 diff_q(&outq, p); 211 } 212 free(q->queue); 213 *q = outq; 214 215 return; 216} 217 218static void merge_broken(struct diff_filepair *p, 219 struct diff_filepair *pp, 220 struct diff_queue_struct *outq) 221{ 222 /* p and pp are broken pairs we want to merge */ 223 struct diff_filepair *c = p, *d = pp; 224 if (DIFF_FILE_VALID(p->one)) { 225 /* this must be a delete half */ 226 d = p; c = pp; 227 } 228 /* Sanity check */ 229 if (!DIFF_FILE_VALID(d->one)) 230 die("internal error in merge #1"); 231 if (DIFF_FILE_VALID(d->two)) 232 die("internal error in merge #2"); 233 if (DIFF_FILE_VALID(c->one)) 234 die("internal error in merge #3"); 235 if (!DIFF_FILE_VALID(c->two)) 236 die("internal error in merge #4"); 237 238 diff_queue(outq, d->one, c->two); 239 diff_free_filespec_data(d->two); 240 diff_free_filespec_data(c->one); 241 free(d); 242 free(c); 243} 244 245void diffcore_merge_broken(void) 246{ 247 struct diff_queue_struct *q = &diff_queued_diff; 248 struct diff_queue_struct outq; 249 int i, j; 250 251 outq.nr = outq.alloc = 0; 252 outq.queue = NULL; 253 254 for (i = 0; i < q->nr; i++) { 255 struct diff_filepair *p = q->queue[i]; 256 if (!p) 257 /* we already merged this with its peer */ 258 continue; 259 else if (p->broken_pair && 260 p->score == 0 && 261 !strcmp(p->one->path, p->two->path)) { 262 /* If the peer also survived rename/copy, then 263 * we merge them back together. 264 */ 265 for (j = i + 1; j < q->nr; j++) { 266 struct diff_filepair *pp = q->queue[j]; 267 if (pp->broken_pair && 268 p->score == 0 && 269 !strcmp(pp->one->path, pp->two->path) && 270 !strcmp(p->one->path, pp->two->path)) { 271 /* Peer survived. Merge them */ 272 merge_broken(p, pp, &outq); 273 q->queue[j] = NULL; 274 break; 275 } 276 } 277 if (q->nr <= j) 278 /* The peer did not survive, so we keep 279 * it in the output. 280 */ 281 diff_q(&outq, p); 282 } 283 else 284 diff_q(&outq, p); 285 } 286 free(q->queue); 287 *q = outq; 288 289 return; 290}