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 (src->sha1_valid && dst->sha1_valid && 62 !memcmp(src->sha1, dst->sha1, 20)) 63 return 0; /* they are the same */ 64 65 if (diff_populate_filespec(src, 0) || diff_populate_filespec(dst, 0)) 66 return 0; /* error but caught downstream */ 67 68 base_size = ((src->size < dst->size) ? src->size : dst->size); 69 if (base_size < MINIMUM_BREAK_SIZE) 70 return 0; /* we do not break too small filepair */ 71 72 delta = diff_delta(src->data, src->size, 73 dst->data, dst->size, 74 &delta_size, 0); 75 if (!delta) 76 return 0; /* error but caught downstream */ 77 78 /* Estimate the edit size by interpreting delta. */ 79 if (count_delta(delta, delta_size, 80 &src_copied, &literal_added)) { 81 free(delta); 82 return 0; /* we cannot tell */ 83 } 84 free(delta); 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 if (src->size <= src_copied) 92 ; /* all copied, nothing removed */ 93 else { 94 delta_size = src->size - src_copied; 95 *merge_score_p = delta_size * MAX_SCORE / src->size; 96 } 97 98 /* Extent of damage, which counts both inserts and 99 * deletes. 100 */ 101 if (src->size + literal_added <= src_copied) 102 delta_size = 0; /* avoid wrapping around */ 103 else 104 delta_size = (src->size - src_copied) + literal_added; 105 106 /* We break if the edit exceeds the minimum. 107 * i.e. (break_score / MAX_SCORE < delta_size / base_size) 108 */ 109 if (break_score * base_size < delta_size * MAX_SCORE) 110 to_break = 1; 111 112 return to_break; 113} 114 115void diffcore_break(int break_score) 116{ 117 struct diff_queue_struct *q = &diff_queued_diff; 118 struct diff_queue_struct outq; 119 120 /* When the filepair has this much edit (insert and delete), 121 * it is first considered to be a rewrite and broken into a 122 * create and delete filepair. This is to help breaking a 123 * file that had too much new stuff added, possibly from 124 * moving contents from another file, so that rename/copy can 125 * match it with the other file. 126 * 127 * int break_score; we reuse incoming parameter for this. 128 */ 129 130 /* After a pair is broken according to break_score and 131 * subjected to rename/copy, both of them may survive intact, 132 * due to lack of suitable rename/copy peer. Or, the caller 133 * may be calling us without using rename/copy. When that 134 * happens, we merge the broken pieces back into one 135 * modification together if the pair did not have more than 136 * this much delete. For this computation, we do not take 137 * insert into account at all. If you start from a 100-line 138 * file and delete 97 lines of it, it does not matter if you 139 * add 27 lines to it to make a new 30-line file or if you add 140 * 997 lines to it to make a 1000-line file. Either way what 141 * you did was a rewrite of 97%. On the other hand, if you 142 * delete 3 lines, keeping 97 lines intact, it does not matter 143 * if you add 3 lines to it to make a new 100-line file or if 144 * you add 903 lines to it to make a new 1000-line file. 145 * Either way you did a lot of additions and not a rewrite. 146 * This merge happens to catch the latter case. A merge_score 147 * of 80% would be a good default value (a broken pair that 148 * has score lower than merge_score will be merged back 149 * together). 150 */ 151 int merge_score; 152 int i; 153 154 /* See comment on DEFAULT_BREAK_SCORE and 155 * DEFAULT_MERGE_SCORE in diffcore.h 156 */ 157 merge_score = (break_score >> 16) & 0xFFFF; 158 break_score = (break_score & 0xFFFF); 159 160 if (!break_score) 161 break_score = DEFAULT_BREAK_SCORE; 162 if (!merge_score) 163 merge_score = DEFAULT_MERGE_SCORE; 164 165 outq.nr = outq.alloc = 0; 166 outq.queue = NULL; 167 168 for (i = 0; i < q->nr; i++) { 169 struct diff_filepair *p = q->queue[i]; 170 int score; 171 172 /* We deal only with in-place edit of non directory. 173 * We do not break anything else. 174 */ 175 if (DIFF_FILE_VALID(p->one) && DIFF_FILE_VALID(p->two) && 176 !S_ISDIR(p->one->mode) && !S_ISDIR(p->two->mode) && 177 !strcmp(p->one->path, p->two->path)) { 178 if (should_break(p->one, p->two, 179 break_score, &score)) { 180 /* Split this into delete and create */ 181 struct diff_filespec *null_one, *null_two; 182 struct diff_filepair *dp; 183 184 /* Set score to 0 for the pair that 185 * needs to be merged back together 186 * should they survive rename/copy. 187 * Also we do not want to break very 188 * small files. 189 */ 190 if (score < merge_score) 191 score = 0; 192 193 /* deletion of one */ 194 null_one = alloc_filespec(p->one->path); 195 dp = diff_queue(&outq, p->one, null_one); 196 dp->score = score; 197 dp->broken_pair = 1; 198 199 /* creation of two */ 200 null_two = alloc_filespec(p->two->path); 201 dp = diff_queue(&outq, null_two, p->two); 202 dp->score = score; 203 dp->broken_pair = 1; 204 205 free(p); /* not diff_free_filepair(), we are 206 * reusing one and two here. 207 */ 208 continue; 209 } 210 } 211 diff_q(&outq, p); 212 } 213 free(q->queue); 214 *q = outq; 215 216 return; 217} 218 219static void merge_broken(struct diff_filepair *p, 220 struct diff_filepair *pp, 221 struct diff_queue_struct *outq) 222{ 223 /* p and pp are broken pairs we want to merge */ 224 struct diff_filepair *c = p, *d = pp, *dp; 225 if (DIFF_FILE_VALID(p->one)) { 226 /* this must be a delete half */ 227 d = p; c = pp; 228 } 229 /* Sanity check */ 230 if (!DIFF_FILE_VALID(d->one)) 231 die("internal error in merge #1"); 232 if (DIFF_FILE_VALID(d->two)) 233 die("internal error in merge #2"); 234 if (DIFF_FILE_VALID(c->one)) 235 die("internal error in merge #3"); 236 if (!DIFF_FILE_VALID(c->two)) 237 die("internal error in merge #4"); 238 239 dp = diff_queue(outq, d->one, c->two); 240 dp->score = p->score; 241 diff_free_filespec_data(d->two); 242 diff_free_filespec_data(c->one); 243 free(d); 244 free(c); 245} 246 247void diffcore_merge_broken(void) 248{ 249 struct diff_queue_struct *q = &diff_queued_diff; 250 struct diff_queue_struct outq; 251 int i, j; 252 253 outq.nr = outq.alloc = 0; 254 outq.queue = NULL; 255 256 for (i = 0; i < q->nr; i++) { 257 struct diff_filepair *p = q->queue[i]; 258 if (!p) 259 /* we already merged this with its peer */ 260 continue; 261 else if (p->broken_pair && 262 !strcmp(p->one->path, p->two->path)) { 263 /* If the peer also survived rename/copy, then 264 * we merge them back together. 265 */ 266 for (j = i + 1; j < q->nr; j++) { 267 struct diff_filepair *pp = q->queue[j]; 268 if (pp->broken_pair && 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}