Annotation of src/usr.bin/less/linenum.c, Revision 1.4
1.1 etheisen 1: /*
1.4 ! millert 2: * Copyright (C) 1984-2002 Mark Nudelman
1.1 etheisen 3: *
1.4 ! millert 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.
1.1 etheisen 6: *
1.4 ! millert 7: * For more information about less, or for information on how to
! 8: * contact the author, see the README file.
1.1 etheisen 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: */
1.4 ! millert 42: struct linenum_info
1.1 etheisen 43: {
1.4 ! millert 44: struct linenum_info *next; /* Link to next in the list */
! 45: struct linenum_info *prev; /* Line to previous in the list */
1.1 etheisen 46: POSITION pos; /* File position */
47: POSITION gap; /* Gap between prev and next */
1.4 ! millert 48: LINENUM line; /* Line number */
1.1 etheisen 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:
1.4 ! millert 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 */
1.1 etheisen 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: {
1.4 ! millert 80: register struct linenum_info *p;
1.1 etheisen 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)
1.4 ! millert 107: register struct linenum_info *p;
1.1 etheisen 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
1.4 ! millert 126: add_lnum(linenum, pos)
! 127: LINENUM linenum;
1.1 etheisen 128: POSITION pos;
129: {
1.4 ! millert 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;
1.1 etheisen 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)
1.4 ! millert 141: if (p->line == linenum)
1.1 etheisen 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;
1.4 ! millert 172: new->line = linenum;
1.1 etheisen 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: */
1.4 ! millert 256: public LINENUM
1.1 etheisen 257: find_linenum(pos)
258: POSITION pos;
259: {
1.4 ! millert 260: register struct linenum_info *p;
! 261: register LINENUM linenum;
1.1 etheisen 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;
1.4 ! millert 312: for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
1.1 etheisen 313: {
314: /*
315: * Allow a signal to abort this loop.
316: */
317: cpos = forw_raw_line(cpos, (char **)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: */
1.4 ! millert 326: add_lnum(linenum, cpos);
1.1 etheisen 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)
1.4 ! millert 332: linenum--;
1.1 etheisen 333: } else
334: {
335: /*
336: * Go backward.
337: */
338: if (ch_seek(p->pos))
339: return (0);
340: loopcount = 0;
1.4 ! millert 341: for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
1.1 etheisen 342: {
343: /*
344: * Allow a signal to abort this loop.
345: */
346: cpos = back_raw_line(cpos, (char **)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: */
1.4 ! millert 355: add_lnum(linenum, cpos);
1.1 etheisen 356: }
357:
1.4 ! millert 358: return (linenum);
1.1 etheisen 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
1.4 ! millert 366: find_pos(linenum)
! 367: LINENUM linenum;
1.1 etheisen 368: {
1.4 ! millert 369: register struct linenum_info *p;
1.1 etheisen 370: POSITION cpos;
1.4 ! millert 371: LINENUM clinenum;
1.1 etheisen 372:
1.4 ! millert 373: if (linenum <= 1)
1.1 etheisen 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: */
1.4 ! millert 382: for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
1.1 etheisen 383: continue;
1.4 ! millert 384: if (p->line == linenum)
1.1 etheisen 385: /* Found it exactly. */
386: return (p->pos);
387:
1.4 ! millert 388: if (p == &anchor || linenum - p->prev->line < p->line - linenum)
1.1 etheisen 389: {
390: /*
391: * Go forward.
392: */
393: p = p->prev;
394: if (ch_seek(p->pos))
395: return (NULL_POSITION);
1.4 ! millert 396: for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
1.1 etheisen 397: {
398: /*
399: * Allow a signal to abort this loop.
400: */
401: cpos = forw_raw_line(cpos, (char **)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);
1.4 ! millert 412: for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
1.1 etheisen 413: {
414: /*
415: * Allow a signal to abort this loop.
416: */
417: cpos = back_raw_line(cpos, (char **)NULL);
418: if (ABORT_SIGS() || cpos == NULL_POSITION)
419: return (NULL_POSITION);
420: }
421: }
422: /*
423: * We might as well cache it.
424: */
1.4 ! millert 425: add_lnum(clinenum, cpos);
1.1 etheisen 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: */
1.4 ! millert 434: public LINENUM
1.1 etheisen 435: currline(where)
436: int where;
437: {
438: POSITION pos;
439: POSITION len;
1.4 ! millert 440: LINENUM linenum;
1.1 etheisen 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;
1.4 ! millert 448: linenum = find_linenum(pos);
1.1 etheisen 449: if (pos == len)
1.4 ! millert 450: linenum--;
! 451: return (linenum);
1.1 etheisen 452: }
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