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-rwxr-xr-xlinenum.c470
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diff --git a/linenum.c b/linenum.c
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+/*
+ * Copyright (C) 1984-2012 Mark Nudelman
+ *
+ * You may distribute under the terms of either the GNU General Public
+ * License or the Less License, as specified in the README file.
+ *
+ * For more information, see the README file.
+ */
+
+
+/*
+ * Code to handle displaying line numbers.
+ *
+ * Finding the line number of a given file position is rather tricky.
+ * We don't want to just start at the beginning of the file and
+ * count newlines, because that is slow for large files (and also
+ * wouldn't work if we couldn't get to the start of the file; e.g.
+ * if input is a long pipe).
+ *
+ * So we use the function add_lnum to cache line numbers.
+ * We try to be very clever and keep only the more interesting
+ * line numbers when we run out of space in our table. A line
+ * number is more interesting than another when it is far from
+ * other line numbers. For example, we'd rather keep lines
+ * 100,200,300 than 100,101,300. 200 is more interesting than
+ * 101 because 101 can be derived very cheaply from 100, while
+ * 200 is more expensive to derive from 100.
+ *
+ * The function currline() returns the line number of a given
+ * position in the file. As a side effect, it calls add_lnum
+ * to cache the line number. Therefore currline is occasionally
+ * called to make sure we cache line numbers often enough.
+ */
+
+#include "less.h"
+
+/*
+ * Structure to keep track of a line number and the associated file position.
+ * A doubly-linked circular list of line numbers is kept ordered by line number.
+ */
+struct linenum_info
+{
+ struct linenum_info *next; /* Link to next in the list */
+ struct linenum_info *prev; /* Line to previous in the list */
+ POSITION pos; /* File position */
+ POSITION gap; /* Gap between prev and next */
+ LINENUM line; /* Line number */
+};
+/*
+ * "gap" needs some explanation: the gap of any particular line number
+ * is the distance between the previous one and the next one in the list.
+ * ("Distance" means difference in file position.) In other words, the
+ * gap of a line number is the gap which would be introduced if this
+ * line number were deleted. It is used to decide which one to replace
+ * when we have a new one to insert and the table is full.
+ */
+
+#define NPOOL 200 /* Size of line number pool */
+
+#define LONGTIME (2) /* In seconds */
+
+static struct linenum_info anchor; /* Anchor of the list */
+static struct linenum_info *freelist; /* Anchor of the unused entries */
+static struct linenum_info pool[NPOOL]; /* The pool itself */
+static struct linenum_info *spare; /* We always keep one spare entry */
+
+extern int linenums;
+extern int sigs;
+extern int sc_height;
+extern int screen_trashed;
+
+/*
+ * Initialize the line number structures.
+ */
+ public void
+clr_linenum()
+{
+ register struct linenum_info *p;
+
+ /*
+ * Put all the entries on the free list.
+ * Leave one for the "spare".
+ */
+ for (p = pool; p < &pool[NPOOL-2]; p++)
+ p->next = p+1;
+ pool[NPOOL-2].next = NULL;
+ freelist = pool;
+
+ spare = &pool[NPOOL-1];
+
+ /*
+ * Initialize the anchor.
+ */
+ anchor.next = anchor.prev = &anchor;
+ anchor.gap = 0;
+ anchor.pos = (POSITION)0;
+ anchor.line = 1;
+}
+
+/*
+ * Calculate the gap for an entry.
+ */
+ static void
+calcgap(p)
+ register struct linenum_info *p;
+{
+ /*
+ * Don't bother to compute a gap for the anchor.
+ * Also don't compute a gap for the last one in the list.
+ * The gap for that last one should be considered infinite,
+ * but we never look at it anyway.
+ */
+ if (p == &anchor || p->next == &anchor)
+ return;
+ p->gap = p->next->pos - p->prev->pos;
+}
+
+/*
+ * Add a new line number to the cache.
+ * The specified position (pos) should be the file position of the
+ * FIRST character in the specified line.
+ */
+ public void
+add_lnum(linenum, pos)
+ LINENUM linenum;
+ POSITION pos;
+{
+ register struct linenum_info *p;
+ register struct linenum_info *new;
+ register struct linenum_info *nextp;
+ register struct linenum_info *prevp;
+ register POSITION mingap;
+
+ /*
+ * Find the proper place in the list for the new one.
+ * The entries are sorted by position.
+ */
+ for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
+ if (p->line == linenum)
+ /* We already have this one. */
+ return;
+ nextp = p;
+ prevp = p->prev;
+
+ if (freelist != NULL)
+ {
+ /*
+ * We still have free (unused) entries.
+ * Use one of them.
+ */
+ new = freelist;
+ freelist = freelist->next;
+ } else
+ {
+ /*
+ * No free entries.
+ * Use the "spare" entry.
+ */
+ new = spare;
+ spare = NULL;
+ }
+
+ /*
+ * Fill in the fields of the new entry,
+ * and insert it into the proper place in the list.
+ */
+ new->next = nextp;
+ new->prev = prevp;
+ new->pos = pos;
+ new->line = linenum;
+
+ nextp->prev = new;
+ prevp->next = new;
+
+ /*
+ * Recalculate gaps for the new entry and the neighboring entries.
+ */
+ calcgap(new);
+ calcgap(nextp);
+ calcgap(prevp);
+
+ if (spare == NULL)
+ {
+ /*
+ * We have used the spare entry.
+ * Scan the list to find the one with the smallest
+ * gap, take it out and make it the spare.
+ * We should never remove the last one, so stop when
+ * we get to p->next == &anchor. This also avoids
+ * looking at the gap of the last one, which is
+ * not computed by calcgap.
+ */
+ mingap = anchor.next->gap;
+ for (p = anchor.next; p->next != &anchor; p = p->next)
+ {
+ if (p->gap <= mingap)
+ {
+ spare = p;
+ mingap = p->gap;
+ }
+ }
+ spare->next->prev = spare->prev;
+ spare->prev->next = spare->next;
+ }
+}
+
+/*
+ * If we get stuck in a long loop trying to figure out the
+ * line number, print a message to tell the user what we're doing.
+ */
+ static void
+longloopmessage()
+{
+ ierror("Calculating line numbers", NULL_PARG);
+}
+
+static int loopcount;
+#if HAVE_TIME
+static long startime;
+#endif
+
+ static void
+longish()
+{
+#if HAVE_TIME
+ if (loopcount >= 0 && ++loopcount > 100)
+ {
+ loopcount = 0;
+ if (get_time() >= startime + LONGTIME)
+ {
+ longloopmessage();
+ loopcount = -1;
+ }
+ }
+#else
+ if (loopcount >= 0 && ++loopcount > LONGLOOP)
+ {
+ longloopmessage();
+ loopcount = -1;
+ }
+#endif
+}
+
+/*
+ * Turn off line numbers because the user has interrupted
+ * a lengthy line number calculation.
+ */
+ static void
+abort_long()
+{
+ if (linenums == OPT_ONPLUS)
+ /*
+ * We were displaying line numbers, so need to repaint.
+ */
+ screen_trashed = 1;
+ linenums = 0;
+ error("Line numbers turned off", NULL_PARG);
+}
+
+/*
+ * Find the line number associated with a given position.
+ * Return 0 if we can't figure it out.
+ */
+ public LINENUM
+find_linenum(pos)
+ POSITION pos;
+{
+ register struct linenum_info *p;
+ register LINENUM linenum;
+ POSITION cpos;
+
+ if (!linenums)
+ /*
+ * We're not using line numbers.
+ */
+ return (0);
+ if (pos == NULL_POSITION)
+ /*
+ * Caller doesn't know what he's talking about.
+ */
+ return (0);
+ if (pos <= ch_zero())
+ /*
+ * Beginning of file is always line number 1.
+ */
+ return (1);
+
+ /*
+ * Find the entry nearest to the position we want.
+ */
+ for (p = anchor.next; p != &anchor && p->pos < pos; p = p->next)
+ continue;
+ if (p->pos == pos)
+ /* Found it exactly. */
+ return (p->line);
+
+ /*
+ * This is the (possibly) time-consuming part.
+ * We start at the line we just found and start
+ * reading the file forward or backward till we
+ * get to the place we want.
+ *
+ * First decide whether we should go forward from the
+ * previous one or backwards from the next one.
+ * The decision is based on which way involves
+ * traversing fewer bytes in the file.
+ */
+#if HAVE_TIME
+ startime = get_time();
+#endif
+ if (p == &anchor || pos - p->prev->pos < p->pos - pos)
+ {
+ /*
+ * Go forward.
+ */
+ p = p->prev;
+ if (ch_seek(p->pos))
+ return (0);
+ loopcount = 0;
+ for (linenum = p->line, cpos = p->pos; cpos < pos; linenum++)
+ {
+ /*
+ * Allow a signal to abort this loop.
+ */
+ cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
+ if (ABORT_SIGS()) {
+ abort_long();
+ return (0);
+ }
+ if (cpos == NULL_POSITION)
+ return (0);
+ longish();
+ }
+ /*
+ * We might as well cache it.
+ */
+ add_lnum(linenum, cpos);
+ /*
+ * If the given position is not at the start of a line,
+ * make sure we return the correct line number.
+ */
+ if (cpos > pos)
+ linenum--;
+ } else
+ {
+ /*
+ * Go backward.
+ */
+ if (ch_seek(p->pos))
+ return (0);
+ loopcount = 0;
+ for (linenum = p->line, cpos = p->pos; cpos > pos; linenum--)
+ {
+ /*
+ * Allow a signal to abort this loop.
+ */
+ cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
+ if (ABORT_SIGS()) {
+ abort_long();
+ return (0);
+ }
+ if (cpos == NULL_POSITION)
+ return (0);
+ longish();
+ }
+ /*
+ * We might as well cache it.
+ */
+ add_lnum(linenum, cpos);
+ }
+
+ return (linenum);
+}
+
+/*
+ * Find the position of a given line number.
+ * Return NULL_POSITION if we can't figure it out.
+ */
+ public POSITION
+find_pos(linenum)
+ LINENUM linenum;
+{
+ register struct linenum_info *p;
+ POSITION cpos;
+ LINENUM clinenum;
+
+ if (linenum <= 1)
+ /*
+ * Line number 1 is beginning of file.
+ */
+ return (ch_zero());
+
+ /*
+ * Find the entry nearest to the line number we want.
+ */
+ for (p = anchor.next; p != &anchor && p->line < linenum; p = p->next)
+ continue;
+ if (p->line == linenum)
+ /* Found it exactly. */
+ return (p->pos);
+
+ if (p == &anchor || linenum - p->prev->line < p->line - linenum)
+ {
+ /*
+ * Go forward.
+ */
+ p = p->prev;
+ if (ch_seek(p->pos))
+ return (NULL_POSITION);
+ for (clinenum = p->line, cpos = p->pos; clinenum < linenum; clinenum++)
+ {
+ /*
+ * Allow a signal to abort this loop.
+ */
+ cpos = forw_raw_line(cpos, (char **)NULL, (int *)NULL);
+ if (ABORT_SIGS())
+ return (NULL_POSITION);
+ if (cpos == NULL_POSITION)
+ return (NULL_POSITION);
+ }
+ } else
+ {
+ /*
+ * Go backward.
+ */
+ if (ch_seek(p->pos))
+ return (NULL_POSITION);
+ for (clinenum = p->line, cpos = p->pos; clinenum > linenum; clinenum--)
+ {
+ /*
+ * Allow a signal to abort this loop.
+ */
+ cpos = back_raw_line(cpos, (char **)NULL, (int *)NULL);
+ if (ABORT_SIGS())
+ return (NULL_POSITION);
+ if (cpos == NULL_POSITION)
+ return (NULL_POSITION);
+ }
+ }
+ /*
+ * We might as well cache it.
+ */
+ add_lnum(clinenum, cpos);
+ return (cpos);
+}
+
+/*
+ * Return the line number of the "current" line.
+ * The argument "where" tells which line is to be considered
+ * the "current" line (e.g. TOP, BOTTOM, MIDDLE, etc).
+ */
+ public LINENUM
+currline(where)
+ int where;
+{
+ POSITION pos;
+ POSITION len;
+ LINENUM linenum;
+
+ pos = position(where);
+ len = ch_length();
+ while (pos == NULL_POSITION && where >= 0 && where < sc_height)
+ pos = position(++where);
+ if (pos == NULL_POSITION)
+ pos = len;
+ linenum = find_linenum(pos);
+ if (pos == len)
+ linenum--;
+ return (linenum);
+}
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