1 /* 2 * Copyright (C) 1984-2007 Mark Nudelman 3 * 4 * You may distribute under the terms of either the GNU General Public 5 * License or the Less License, as specified in the README file. 6 * 7 * For more information about less, or for information on how to 8 * contact the author, see the README file. 9 */ 10 11 12 /* 13 * Code to handle displaying line numbers. 14 * 15 * Finding the line number of a given file position is rather tricky. 16 * We don't want to just start at the beginning of the file and 17 * count newlines, because that is slow for large files (and also 18 * wouldn't work if we couldn't get to the start of the file; e.g. 19 * if input is a long pipe). 20 * 21 * So we use the function add_lnum to cache line numbers. 22 * We try to be very clever and keep only the more interesting 23 * line numbers when we run out of space in our table. A line 24 * number is more interesting than another when it is far from 25 * other line numbers. For example, we'd rather keep lines 26 * 100,200,300 than 100,101,300. 200 is more interesting than 27 * 101 because 101 can be derived very cheaply from 100, while 28 * 200 is more expensive to derive from 100. 29 * 30 * The function currline() returns the line number of a given 31 * position in the file. As a side effect, it calls add_lnum 32 * to cache the line number. Therefore currline is occasionally 33 * called to make sure we cache line numbers often enough. 34 */ 35 36 #include "less.h" 37 38 /* 39 * Structure to keep track of a line number and the associated file position. 40 * A doubly-linked circular list of line numbers is kept ordered by line number. 41 */ 42 struct linenum_info 43 { 44 struct linenum_info *next; /* Link to next in the list */ 45 struct linenum_info *prev; /* Line to previous in the list */ 46 POSITION pos; /* File position */ 47 POSITION gap; /* Gap between prev and next */ 48 LINENUM line; /* Line number */ 49 }; 50 /* 51 * "gap" needs some explanation: the gap of any particular line number 52 * is the distance between the previous one and the next one in the list. 53 * ("Distance" means difference in file position.) In other words, the 54 * gap of a line number is the gap which would be introduced if this 55 * line number were deleted. It is used to decide which one to replace 56 * when we have a new one to insert and the table is full. 57 */ 58 59 #define NPOOL 50 /* Size of line number pool */ 60 61 #define LONGTIME (2) /* In seconds */ 62 63 public int lnloop = 0; /* Are we in the line num loop? */ 64 65 static struct linenum_info anchor; /* Anchor of the list */ 66 static struct linenum_info *freelist; /* Anchor of the unused entries */ 67 static struct linenum_info pool[NPOOL]; /* The pool itself */ 68 static struct linenum_info *spare; /* We always keep one spare entry */ 69 70 extern int linenums; 71 extern int sigs; 72 extern int sc_height; 73 74 /* 75 * Initialize the line number structures. 76 */ 77 public void 78 clr_linenum() 79 { 80 register struct linenum_info *p; 81 82 /* 83 * Put all the entries on the free list. 84 * Leave one for the "spare". 85 */ 86 for (p = pool; p < &pool[NPOOL-2]; p++) 87 p->next = p+1; 88 pool[NPOOL-2].next = NULL; 89 freelist = pool; 90 91 spare = &pool[NPOOL-1]; 92 93 /* 94 * Initialize the anchor. 95 */ 96 anchor.next = anchor.prev = &anchor; 97 anchor.gap = 0; 98 anchor.pos = (POSITION)0; 99 anchor.line = 1; 100 } 101 102 /* 103 * Calculate the gap for an entry. 104 */ 105 static void 106 calcgap(p) 107 register struct linenum_info *p; 108 { 109 /* 110 * Don't bother to compute a gap for the anchor. 111 * Also don't compute a gap for the last one in the list. 112 * The gap for that last one should be considered infinite, 113 * but we never look at it anyway. 114 */ 115 if (p == &anchor || p->next == &anchor) 116 return; 117 p->gap = p->next->pos - p->prev->pos; 118 } 119 120 /* 121 * Add a new line number to the cache. 122 * The specified position (pos) should be the file position of the 123 * FIRST character in the specified line. 124 */ 125 public void 126 add_lnum(linenum, pos) 127 LINENUM linenum; 128 POSITION pos; 129 { 130 register struct linenum_info *p; 131 register struct linenum_info *new; 132 register struct linenum_info *nextp; 133 register struct linenum_info *prevp; 134 register POSITION mingap; 135 136 /* 137 * Find the proper place in the list for the new one. 138 * The entries are sorted by position. 139 */ 140 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next) 141 if (p->line == linenum) 142 /* We already have this one. */ 143 return; 144 nextp = p; 145 prevp = p->prev; 146 147 if (freelist != NULL) 148 { 149 /* 150 * We still have free (unused) entries. 151 * Use one of them. 152 */ 153 new = freelist; 154 freelist = freelist->next; 155 } else 156 { 157 /* 158 * No free entries. 159 * Use the "spare" entry. 160 */ 161 new = spare; 162 spare = NULL; 163 } 164 165 /* 166 * Fill in the fields of the new entry, 167 * and insert it into the proper place in the list. 168 */ 169 new->next = nextp; 170 new->prev = prevp; 171 new->pos = pos; 172 new->line = linenum; 173 174 nextp->prev = new; 175 prevp->next = new; 176 177 /* 178 * Recalculate gaps for the new entry and the neighboring entries. 179 */ 180 calcgap(new); 181 calcgap(nextp); 182 calcgap(prevp); 183 184 if (spare == NULL) 185 { 186 /* 187 * We have used the spare entry. 188 * Scan the list to find the one with the smallest 189 * gap, take it out and make it the spare. 190 * We should never remove the last one, so stop when 191 * we get to p->next == &anchor. This also avoids 192 * looking at the gap of the last one, which is 193 * not computed by calcgap. 194 */ 195 mingap = anchor.next->gap; 196 for (p = anchor.next; p->next != &anchor; p = p->next) 197 { 198 if (p->gap <= mingap) 199 { 200 spare = p; 201 mingap = p->gap; 202 } 203 } 204 spare->next->prev = spare->prev; 205 spare->prev->next = spare->next; 206 } 207 } 208 209 /* 210 * If we get stuck in a long loop trying to figure out the 211 * line number, print a message to tell the user what we're doing. 212 */ 213 static void 214 longloopmessage() 215 { 216 ierror("Calculating line numbers", NULL_PARG); 217 /* 218 * Set the lnloop flag here, so if the user interrupts while 219 * we are calculating line numbers, the signal handler will 220 * turn off line numbers (linenums=0). 221 */ 222 lnloop = 1; 223 } 224 225 static int loopcount; 226 #if HAVE_TIME 227 static long startime; 228 #endif 229 230 static void 231 longish() 232 { 233 #if HAVE_TIME 234 if (loopcount >= 0 && ++loopcount > 100) 235 { 236 loopcount = 0; 237 if (get_time() >= startime + LONGTIME) 238 { 239 longloopmessage(); 240 loopcount = -1; 241 } 242 } 243 #else 244 if (loopcount >= 0 && ++loopcount > LONGLOOP) 245 { 246 longloopmessage(); 247 loopcount = -1; 248 } 249 #endif 250 } 251 252 /* 253 * Find the line number associated with a given position. 254 * Return 0 if we can't figure it out. 255 */ 256 public LINENUM 257 find_linenum(pos) 258 POSITION pos; 259 { 260 register struct linenum_info *p; 261 register LINENUM linenum; 262 POSITION cpos; 263 264 if (!linenums) 265 /* 266 * We're not using line numbers. 267 */ 268 return (0); 269 if (pos == NULL_POSITION) 270 /* 271 * Caller doesn't know what he's talking about. 272 */ 273 return (0); 274 if (pos <= ch_zero()) 275 /* 276 * Beginning of file is always line number 1. 277 */ 278 return (1); 279 280 /* 281 * Find the entry nearest to the position we want. 282 */ 283 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next) 284 continue; 285 if (p->pos == pos) 286 /* Found it exactly. */ 287 return (p->line); 288 289 /* 290 * This is the (possibly) time-consuming part. 291 * We start at the line we just found and start 292 * reading the file forward or backward till we 293 * get to the place we want. 294 * 295 * First decide whether we should go forward from the 296 * previous one or backwards from the next one. 297 * The decision is based on which way involves 298 * traversing fewer bytes in the file. 299 */ 300 #if HAVE_TIME 301 startime = get_time(); 302 #endif 303 if (p == &anchor || pos - p->prev->pos < p->pos - pos) 304 { 305 /* 306 * Go forward. 307 */ 308 p = p->prev; 309 if (ch_seek(p->pos)) 310 return (0); 311 loopcount = 0; 312 for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++) 313 { 314 /* 315 * Allow a signal to abort this loop. 316 */ 317 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL); 318 if (ABORT_SIGS() || cpos == NULL_POSITION) 319 return (0); 320 longish(); 321 } 322 lnloop = 0; 323 /* 324 * We might as well cache it. 325 */ 326 add_lnum(linenum, cpos); 327 /* 328 * If the given position is not at the start of a line, 329 * make sure we return the correct line number. 330 */ 331 if (cpos > pos) 332 linenum--; 333 } else 334 { 335 /* 336 * Go backward. 337 */ 338 if (ch_seek(p->pos)) 339 return (0); 340 loopcount = 0; 341 for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--) 342 { 343 /* 344 * Allow a signal to abort this loop. 345 */ 346 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL); 347 if (ABORT_SIGS() || cpos == NULL_POSITION) 348 return (0); 349 longish(); 350 } 351 lnloop = 0; 352 /* 353 * We might as well cache it. 354 */ 355 add_lnum(linenum, cpos); 356 } 357 358 return (linenum); 359 } 360 361 /* 362 * Find the position of a given line number. 363 * Return NULL_POSITION if we can't figure it out. 364 */ 365 public POSITION 366 find_pos(linenum) 367 LINENUM linenum; 368 { 369 register struct linenum_info *p; 370 POSITION cpos; 371 LINENUM clinenum; 372 373 if (linenum <= 1) 374 /* 375 * Line number 1 is beginning of file. 376 */ 377 return (ch_zero()); 378 379 /* 380 * Find the entry nearest to the line number we want. 381 */ 382 for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next) 383 continue; 384 if (p->line == linenum) 385 /* Found it exactly. */ 386 return (p->pos); 387 388 if (p == &anchor || linenum - p->prev->line < p->line - linenum) 389 { 390 /* 391 * Go forward. 392 */ 393 p = p->prev; 394 if (ch_seek(p->pos)) 395 return (NULL_POSITION); 396 for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++) 397 { 398 /* 399 * Allow a signal to abort this loop. 400 */ 401 cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL); 402 if (ABORT_SIGS() || cpos == NULL_POSITION) 403 return (NULL_POSITION); 404 } 405 } else 406 { 407 /* 408 * Go backward. 409 */ 410 if (ch_seek(p->pos)) 411 return (NULL_POSITION); 412 for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--) 413 { 414 /* 415 * Allow a signal to abort this loop. 416 */ 417 cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL); 418 if (ABORT_SIGS() || cpos == NULL_POSITION) 419 return (NULL_POSITION); 420 } 421 } 422 /* 423 * We might as well cache it. 424 */ 425 add_lnum(clinenum, cpos); 426 return (cpos); 427 } 428 429 /* 430 * Return the line number of the "current" line. 431 * The argument "where" tells which line is to be considered 432 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc). 433 */ 434 public LINENUM 435 currline(where) 436 int where; 437 { 438 POSITION pos; 439 POSITION len; 440 LINENUM linenum; 441 442 pos = position(where); 443 len = ch_length(); 444 while (pos == NULL_POSITION && where >= 0 && where < sc_height) 445 pos = position(++where); 446 if (pos == NULL_POSITION) 447 pos = len; 448 linenum = find_linenum(pos); 449 if (pos == len) 450 linenum--; 451 return (linenum); 452 } 453