import less(1)

[unleashed/tickless.git] / bin / less / linenum.c

/*
 * Copyright (C) 1984-2012  Mark Nudelman
 * Modified for use with illumos by Garrett D'Amore.
 * Copyright 2014 Garrett D'Amore <garrett@damore.org>
 *
 * 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 <sys/time.h>

#include <time.h>

#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 */
        off_t pos;                      /* File position */
        off_t gap;                      /* Gap between prev and next */
        off_t 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 volatile sig_atomic_t sigs;
extern int sc_height;
extern int screen_trashed;

/*
 * Initialize the line number structures.
 */
void
clr_linenum(void)
{
        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 = 0;
        anchor.line = 1;
}

/*
 * Calculate the gap for an entry.
 */
static void
calcgap(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.
 */
void
add_lnum(off_t linenum, off_t pos)
{
        struct linenum_info *p;
        struct linenum_info *new;
        struct linenum_info *nextp;
        struct linenum_info *prevp;
        off_t 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;
        }
}

static int loopcount;
static struct timespec timeout;

static void
timeout_set(int seconds)
{
        clock_gettime(CLOCK_MONOTONIC, &timeout);
        timeout.tv_sec += seconds;
}

static int
timeout_elapsed(void)
{
        struct timespec now;

        clock_gettime(CLOCK_MONOTONIC, &now);
        return timespeccmp(&now, &timeout, >=);
}

static void
longish(void)
{
        if (loopcount >= 0 && ++loopcount > 100) {
                loopcount = 0;
                if (timeout_elapsed()) {
                        ierror("Calculating line numbers", NULL);
                        loopcount = -1;
                }
        }
}

/*
 * Turn off line numbers because the user has interrupted
 * a lengthy line number calculation.
 */
static void
abort_long(void)
{
        if (linenums == OPT_ONPLUS)
                /*
                 * We were displaying line numbers, so need to repaint.
                 */
                screen_trashed = 1;
        linenums = 0;
        error("Line numbers turned off", NULL);
}

/*
 * Find the line number associated with a given position.
 * Return 0 if we can't figure it out.
 */
off_t
find_linenum(off_t pos)
{
        struct linenum_info *p;
        off_t linenum;
        off_t cpos;

        if (!linenums)
                /*
                 * We're not using line numbers.
                 */
                return (0);
        if (pos == -1)
                /*
                 * 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.
         */
        timeout_set(LONGTIME);
        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, NULL, NULL);
                        if (ABORT_SIGS()) {
                                abort_long();
                                return (0);
                        }
                        if (cpos == -1)
                                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, NULL, NULL);
                        if (ABORT_SIGS()) {
                                abort_long();
                                return (0);
                        }
                        if (cpos == -1)
                                return (0);
                        longish();
                }
                /*
                 * We might as well cache it.
                 */
                add_lnum(linenum, cpos);
        }

        return (linenum);
}

/*
 * Find the position of a given line number.
 * Return -1 if we can't figure it out.
 */
off_t
find_pos(off_t linenum)
{
        struct linenum_info *p;
        off_t cpos;
        off_t 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 (-1);
                for (clinenum = p->line, cpos = p->pos;
                    clinenum < linenum;
                    clinenum++) {
                        /*
                         * Allow a signal to abort this loop.
                         */
                        cpos = forw_raw_line(cpos, NULL, NULL);
                        if (ABORT_SIGS())
                                return (-1);
                        if (cpos == -1)
                                return (-1);
                }
        } else {
                /*
                 * Go backward.
                 */
                if (ch_seek(p->pos))
                        return (-1);
                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 (-1);
                        if (cpos == -1)
                                return (-1);
                }
        }
        /*
         * 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).
 */
off_t
currline(int where)
{
        off_t pos;
        off_t len;
        off_t linenum;

        pos = position(where);
        len = ch_length();
        while (pos == -1 && where >= 0 && where < sc_height)
                pos = position(++where);
        if (pos == -1)
                pos = len;
        linenum = find_linenum(pos);
        if (pos == len)
                linenum--;
        return (linenum);
}