1 /* $NetBSD: linenum.c,v 1.5 2003/10/13 14:34:25 agc Exp $ */ 2 3 /* 4 * Copyright (c) 1988 Mark Nudelman 5 * Copyright (c) 1988, 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 1. Redistributions of source code must retain the above copyright 12 * notice, this list of conditions and the following disclaimer. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice, this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 3. Neither the name of the University nor the names of its contributors 17 * may be used to endorse or promote products derived from this software 18 * without specific prior written permission. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30 * SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 #ifndef lint 35 #if 0 36 static char sccsid[] = "@(#)linenum.c 8.1 (Berkeley) 6/6/93"; 37 #else 38 __RCSID("$NetBSD: linenum.c,v 1.5 2003/10/13 14:34:25 agc Exp $"); 39 #endif 40 #endif /* not lint */ 41 42 /* 43 * Code to handle displaying line numbers. 44 * 45 * Finding the line number of a given file position is rather tricky. 46 * We don't want to just start at the beginning of the file and 47 * count newlines, because that is slow for large files (and also 48 * wouldn't work if we couldn't get to the start of the file; e.g. 49 * if input is a long pipe). 50 * 51 * So we use the function add_lnum to cache line numbers. 52 * We try to be very clever and keep only the more interesting 53 * line numbers when we run out of space in our table. A line 54 * number is more interesting than another when it is far from 55 * other line numbers. For example, we'd rather keep lines 56 * 100,200,300 than 100,101,300. 200 is more interesting than 57 * 101 because 101 can be derived very cheaply from 100, while 58 * 200 is more expensive to derive from 100. 59 * 60 * The function currline() returns the line number of a given 61 * position in the file. As a side effect, it calls add_lnum 62 * to cache the line number. Therefore currline is occasionally 63 * called to make sure we cache line numbers often enough. 64 */ 65 66 #include <sys/types.h> 67 #include <stdio.h> 68 #include <time.h> 69 70 #include "less.h" 71 #include "extern.h" 72 73 /* 74 * Structure to keep track of a line number and the associated file position. 75 * A doubly-linked circular list of line numbers is kept ordered by line number. 76 */ 77 struct linenum 78 { 79 struct linenum *next; /* Link to next in the list */ 80 struct linenum *prev; /* Line to previous in the list */ 81 off_t pos; /* File position */ 82 off_t gap; /* Gap between prev and next */ 83 int line; /* Line number */ 84 }; 85 /* 86 * "gap" needs some explanation: the gap of any particular line number 87 * is the distance between the previous one and the next one in the list. 88 * ("Distance" means difference in file position.) In other words, the 89 * gap of a line number is the gap which would be introduced if this 90 * line number were deleted. It is used to decide which one to replace 91 * when we have a new one to insert and the table is full. 92 */ 93 94 #define NPOOL 50 /* Size of line number pool */ 95 96 #define LONGTIME (2) /* In seconds */ 97 98 int lnloop = 0; /* Are we in the line num loop? */ 99 100 static struct linenum anchor; /* Anchor of the list */ 101 static struct linenum *freelist; /* Anchor of the unused entries */ 102 static struct linenum pool[NPOOL]; /* The pool itself */ 103 static struct linenum *spare; /* We always keep one spare entry */ 104 105 static void calcgap __P((struct linenum *)); 106 static void longloopmessage __P((void)); 107 /* 108 * Initialize the line number structures. 109 */ 110 void 111 clr_linenum() 112 { 113 struct linenum *p; 114 115 /* 116 * Put all the entries on the free list. 117 * Leave one for the "spare". 118 */ 119 for (p = pool; p < &pool[NPOOL-2]; p++) 120 p->next = p+1; 121 pool[NPOOL-2].next = NULL; 122 freelist = pool; 123 124 spare = &pool[NPOOL-1]; 125 126 /* 127 * Initialize the anchor. 128 */ 129 anchor.next = anchor.prev = &anchor; 130 anchor.gap = 0; 131 anchor.pos = (off_t)0; 132 anchor.line = 1; 133 } 134 135 /* 136 * Calculate the gap for an entry. 137 */ 138 static void 139 calcgap(p) 140 struct linenum *p; 141 { 142 /* 143 * Don't bother to compute a gap for the anchor. 144 * Also don't compute a gap for the last one in the list. 145 * The gap for that last one should be considered infinite, 146 * but we never look at it anyway. 147 */ 148 if (p == &anchor || p->next == &anchor) 149 return; 150 p->gap = p->next->pos - p->prev->pos; 151 } 152 153 /* 154 * Add a new line number to the cache. 155 * The specified position (pos) should be the file position of the 156 * FIRST character in the specified line. 157 */ 158 void 159 add_lnum(line, pos) 160 int line; 161 off_t pos; 162 { 163 struct linenum *p; 164 struct linenum *new; 165 struct linenum *nextp; 166 struct linenum *prevp; 167 off_t mingap; 168 169 /* 170 * Find the proper place in the list for the new one. 171 * The entries are sorted by position. 172 */ 173 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next) 174 if (p->line == line) 175 /* We already have this one. */ 176 return; 177 nextp = p; 178 prevp = p->prev; 179 180 if (freelist != NULL) 181 { 182 /* 183 * We still have free (unused) entries. 184 * Use one of them. 185 */ 186 new = freelist; 187 freelist = freelist->next; 188 } else 189 { 190 /* 191 * No free entries. 192 * Use the "spare" entry. 193 */ 194 new = spare; 195 spare = NULL; 196 } 197 198 /* 199 * Fill in the fields of the new entry, 200 * and insert it into the proper place in the list. 201 */ 202 new->next = nextp; 203 new->prev = prevp; 204 new->pos = pos; 205 new->line = line; 206 207 nextp->prev = new; 208 prevp->next = new; 209 210 /* 211 * Recalculate gaps for the new entry and the neighboring entries. 212 */ 213 calcgap(new); 214 calcgap(nextp); 215 calcgap(prevp); 216 217 if (spare == NULL) 218 { 219 /* 220 * We have used the spare entry. 221 * Scan the list to find the one with the smallest 222 * gap, take it out and make it the spare. 223 * We should never remove the last one, so stop when 224 * we get to p->next == &anchor. This also avoids 225 * looking at the gap of the last one, which is 226 * not computed by calcgap. 227 */ 228 mingap = anchor.next->gap; 229 for (p = anchor.next; p->next != &anchor; p = p->next) 230 { 231 if (p->gap <= mingap) 232 { 233 spare = p; 234 mingap = p->gap; 235 } 236 } 237 spare->next->prev = spare->prev; 238 spare->prev->next = spare->next; 239 } 240 } 241 242 /* 243 * If we get stuck in a long loop trying to figure out the 244 * line number, print a message to tell the user what we're doing. 245 */ 246 static void 247 longloopmessage() 248 { 249 ierror("Calculating line numbers"); 250 /* 251 * Set the lnloop flag here, so if the user interrupts while 252 * we are calculating line numbers, the signal handler will 253 * turn off line numbers (linenums=0). 254 */ 255 lnloop = 1; 256 } 257 258 /* 259 * Find the line number associated with a given position. 260 * Return 0 if we can't figure it out. 261 */ 262 int 263 find_linenum(pos) 264 off_t pos; 265 { 266 struct linenum *p; 267 int lno; 268 int loopcount; 269 off_t cpos; 270 time_t startime; 271 272 if (!linenums) 273 /* 274 * We're not using line numbers. 275 */ 276 return (0); 277 if (pos == NULL_POSITION) 278 /* 279 * Caller doesn't know what he's talking about. 280 */ 281 return (0); 282 if (pos == (off_t)0) 283 /* 284 * Beginning of file is always line number 1. 285 */ 286 return (1); 287 288 /* 289 * Find the entry nearest to the position we want. 290 */ 291 for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next) 292 continue; 293 if (p->pos == pos) 294 /* Found it exactly. */ 295 return (p->line); 296 297 /* 298 * This is the (possibly) time-consuming part. 299 * We start at the line we just found and start 300 * reading the file forward or backward till we 301 * get to the place we want. 302 * 303 * First decide whether we should go forward from the 304 * previous one or backwards from the next one. 305 * The decision is based on which way involves 306 * traversing fewer bytes in the file. 307 */ 308 flush(); 309 (void)time(&startime); 310 if (p == &anchor || pos - p->prev->pos < p->pos - pos) 311 { 312 /* 313 * Go forward. 314 */ 315 p = p->prev; 316 if (ch_seek(p->pos)) 317 return (0); 318 loopcount = 0; 319 for (lno = p->line, cpos = p->pos; cpos < pos; lno++) 320 { 321 /* 322 * Allow a signal to abort this loop. 323 */ 324 cpos = forw_raw_line(cpos); 325 if (sigs || cpos == NULL_POSITION) 326 return (0); 327 if (loopcount >= 0 && ++loopcount > 100) { 328 loopcount = 0; 329 if (time((time_t *)NULL) 330 >= startime + LONGTIME) { 331 longloopmessage(); 332 loopcount = -1; 333 } 334 } 335 } 336 lnloop = 0; 337 /* 338 * If the given position is not at the start of a line, 339 * make sure we return the correct line number. 340 */ 341 if (cpos > pos) 342 lno--; 343 } else 344 { 345 /* 346 * Go backward. 347 */ 348 if (ch_seek(p->pos)) 349 return (0); 350 loopcount = 0; 351 for (lno = p->line, cpos = p->pos; cpos > pos; lno--) 352 { 353 /* 354 * Allow a signal to abort this loop. 355 */ 356 cpos = back_raw_line(cpos); 357 if (sigs || cpos == NULL_POSITION) 358 return (0); 359 if (loopcount >= 0 && ++loopcount > 100) { 360 loopcount = 0; 361 if (time((time_t *)NULL) 362 >= startime + LONGTIME) { 363 longloopmessage(); 364 loopcount = -1; 365 } 366 } 367 } 368 lnloop = 0; 369 } 370 371 /* 372 * We might as well cache it. 373 */ 374 add_lnum(lno, cpos); 375 return (lno); 376 } 377 378 /* 379 * Return the line number of the "current" line. 380 * The argument "where" tells which line is to be considered 381 * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc). 382 */ 383 int 384 currline(where) 385 int where; 386 { 387 off_t pos; 388 389 if ((pos = position(where)) == NULL_POSITION) 390 pos = ch_length(); 391 return(find_linenum(pos)); 392 } 393