search.c

/*
 * Copyright (C) 1984-2022  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.
 */


/*
 * Routines to search a file for a pattern.
 */

#include "less.h"
#include "position.h"
#include "charset.h"

#define MINPOS(a,b)     (((a) < (b)) ? (a) : (b))
#define MAXPOS(a,b)     (((a) > (b)) ? (a) : (b))

extern int sigs;
extern int how_search;
extern int caseless;
extern int linenums;
extern int sc_height;
extern int jump_sline;
extern int bs_mode;
extern int ctldisp;
extern int status_col;
extern void *ml_search;
extern POSITION start_attnpos;
extern POSITION end_attnpos;
extern int utf_mode;
extern int screen_trashed;
extern int sc_width;
extern int sc_height;
extern int hshift;
#if HILITE_SEARCH
extern int hilite_search;
extern int size_linebuf;
extern int squished;
extern int can_goto_line;
static int hide_hilite;
static POSITION prep_startpos;
static POSITION prep_endpos;
extern POSITION xxpos;

/*
 * Structures for maintaining a set of ranges for hilites and filtered-out
 * lines. Each range is stored as a node within a red-black tree, and we
 * try to extend existing ranges (without creating overlaps) rather than
 * create new nodes if possible. We remember the last node found by a
 * search for constant-time lookup if the next search is near enough to
 * the previous. To aid that, we overlay a secondary doubly-linked list
 * on top of the red-black tree so we can find the preceding/succeeding
 * nodes also in constant time.
 *
 * Each node is allocated from a series of pools, each pool double the size
 * of the previous (for amortised constant time allocation). Since our only
 * tree operations are clear and node insertion, not node removal, we don't
 * need to maintain a usage bitmap or freelist and can just return nodes
 * from the pool in-order until capacity is reached.
 */
struct hilite
{
    POSITION hl_startpos;
    POSITION hl_endpos;
};
struct hilite_node
{
    struct hilite_node *parent;
    struct hilite_node *left;
    struct hilite_node *right;
    struct hilite_node *prev;
    struct hilite_node *next;
    int red;
    struct hilite r;
};
struct hilite_storage
{
    int capacity;
    int used;
    struct hilite_storage *next;
    struct hilite_node *nodes;
};
struct hilite_tree
{
    struct hilite_storage *first;
    struct hilite_storage *current;
    struct hilite_node *root;
    struct hilite_node *lookaside;
};
#define HILITE_INITIALIZER() { NULL, NULL, NULL, NULL }
#define HILITE_LOOKASIDE_STEPS 2

static struct hilite_tree hilite_anchor = HILITE_INITIALIZER();
static struct hilite_tree filter_anchor = HILITE_INITIALIZER();
static struct pattern_info *filter_infos = NULL;

#endif

/*
 * These are the static variables that represent the "remembered"
 * search pattern and filter pattern.
 */
struct pattern_info {
    PATTERN_TYPE compiled;
    char* text;
    int search_type;
    struct pattern_info *next;
};

#if NO_REGEX
#define info_compiled(info) ((void*)0)
#else
#define info_compiled(info) ((info)->compiled)
#endif

static struct pattern_info search_info;
static int is_ucase_pattern;
public int is_caseless;

/*
 * Are there any uppercase letters in this string?
 */
    static int
is_ucase(str)
    char *str;
{
    char *str_end = str + strlen(str);
    LWCHAR ch;

    while (str < str_end)
    {
        ch = step_char(&str, +1, str_end);
        if (IS_UPPER(ch))
            return (1);
    }
    return (0);
}

/*
 * Discard a saved pattern.
 */
    static void
clear_pattern(info)
    struct pattern_info *info;
{
    if (info->text != NULL)
        free(info->text);
    info->text = NULL;
#if !NO_REGEX
    uncompile_pattern(&info->compiled);
#endif
}

/*
 * Compile and save a search pattern.
 */
    static int
set_pattern(info, pattern, search_type, show_error)
    struct pattern_info *info;
    char *pattern;
    int search_type;
    int show_error;
{
    /*
     * Ignore case if -I is set OR
     * -i is set AND the pattern is all lowercase.
     */
    is_ucase_pattern = (pattern == NULL) ? FALSE : is_ucase(pattern);
    is_caseless = (is_ucase_pattern && caseless != OPT_ONPLUS) ? 0 : caseless;
#if !NO_REGEX
    if (pattern == NULL)
        SET_NULL_PATTERN(info->compiled);
    else if (compile_pattern(pattern, search_type, show_error, &info->compiled) < 0)
        return -1;
#endif
    /* Pattern compiled successfully; save the text too. */
    if (info->text != NULL)
        free(info->text);
    info->text = NULL;
    if (pattern != NULL)
    {
        info->text = (char *) ecalloc(1, strlen(pattern)+1);
        strcpy(info->text, pattern);
    }
    info->search_type = search_type;
    return 0;
}

/*
 * Initialize saved pattern to nothing.
 */
    static void
init_pattern(info)
    struct pattern_info *info;
{
    SET_NULL_PATTERN(info->compiled);
    info->text = NULL;
    info->search_type = 0;
    info->next = NULL;
}

/*
 * Initialize search variables.
 */
    public void
init_search(VOID_PARAM)
{
    init_pattern(&search_info);
}

/*
 * Determine which text conversions to perform before pattern matching.
 */
    static int
get_cvt_ops(VOID_PARAM)
{
    int ops = 0;

    if (is_caseless && !re_handles_caseless)
        ops |= CVT_TO_LC;
    if (bs_mode == BS_SPECIAL)
        ops |= CVT_BS;
    if (bs_mode != BS_CONTROL)
        ops |= CVT_CRLF;
    if (ctldisp == OPT_ONPLUS)
        ops |= CVT_ANSI;
    return (ops);
}

/*
 * Is there a previous (remembered) search pattern?
 */
    static int
prev_pattern(info)
    struct pattern_info *info;
{
#if !NO_REGEX
    if ((info->search_type & SRCH_NO_REGEX) == 0)
        return (!is_null_pattern(info->compiled));
#endif
    return (info->text != NULL);
}

#if HILITE_SEARCH
/*
 * Repaint the hilites currently displayed on the screen.
 * Repaint each line which contains highlighted text.
 * If on==0, force all hilites off.
 */
    public void
repaint_hilite(on)
    int on;
{
    int sindex;
    POSITION pos;
    int save_hide_hilite;

    if (squished)
        repaint();

    save_hide_hilite = hide_hilite;
    if (!on)
    {
        if (hide_hilite)
            return;
        hide_hilite = 1;
    }

    if (!can_goto_line)
    {
        repaint();
        hide_hilite = save_hide_hilite;
        return;
    }

    for (sindex = TOP;  sindex < TOP + sc_height-1;  sindex++)
    {
        pos = position(sindex);
        if (pos == NULL_POSITION)
            continue;
        (void) forw_line(pos);
        goto_line(sindex);
        put_line();
    }
    overlay_header();
    lower_left();
    hide_hilite = save_hide_hilite;
}
#endif

/*
 * Clear the attn hilite.
 */
    public void
clear_attn(VOID_PARAM)
{
#if HILITE_SEARCH
    int sindex;
    POSITION old_start_attnpos;
    POSITION old_end_attnpos;
    POSITION pos;
    POSITION epos;
    int moved = 0;

    if (start_attnpos == NULL_POSITION)
        return;
    old_start_attnpos = start_attnpos;
    old_end_attnpos = end_attnpos;
    start_attnpos = end_attnpos = NULL_POSITION;

    if (!can_goto_line)
    {
        repaint();
        return;
    }
    if (squished)
        repaint();

    for (sindex = TOP;  sindex < TOP + sc_height-1;  sindex++)
    {
        pos = position(sindex);
        if (pos == NULL_POSITION)
            continue;
        epos = position(sindex+1);
        if (pos <= old_end_attnpos &&
             (epos == NULL_POSITION || epos > old_start_attnpos))
        {
            (void) forw_line(pos);
            goto_line(sindex);
            put_line();
            moved = 1;
        }
    }
    if (overlay_header())
        moved = 1;
    if (moved)
        lower_left();
#endif
}

/*
 * Toggle or clear search string highlighting.
 */
    public void
undo_search(clear)
    int clear;
{
    clear_pattern(&search_info);
#if HILITE_SEARCH
    if (clear)
    {
        clr_hilite();
    } else
    {
        if (hilite_anchor.first == NULL)
        {
            error("No previous regular expression", NULL_PARG);
            return;
        }
        hide_hilite = !hide_hilite;
    }
    repaint_hilite(1);
#endif
}

#if HILITE_SEARCH
/*
 * Clear the hilite list.
 */
    public void
clr_hlist(anchor)
    struct hilite_tree *anchor;
{
    struct hilite_storage *hls;
    struct hilite_storage *nexthls;

    for (hls = anchor->first;  hls != NULL;  hls = nexthls)
    {
        nexthls = hls->next;
        free((void*)hls->nodes);
        free((void*)hls);
    }
    anchor->first = NULL;
    anchor->current = NULL;
    anchor->root = NULL;

    anchor->lookaside = NULL;

    prep_startpos = prep_endpos = NULL_POSITION;
}

    public void
clr_hilite(VOID_PARAM)
{
    clr_hlist(&hilite_anchor);
}

    public void
clr_filter(VOID_PARAM)
{
    clr_hlist(&filter_anchor);
}

    struct hilite_node*
hlist_last(anchor)
    struct hilite_tree *anchor;
{
    struct hilite_node *n = anchor->root;
    while (n != NULL && n->right != NULL)
        n = n->right;
    return n;
}

    struct hilite_node*
hlist_next(n)
    struct hilite_node *n;
{
    return n->next;
}

    struct hilite_node*
hlist_prev(n)
    struct hilite_node *n;
{
    return n->prev;
}

/*
 * Find the node covering pos, or the node after it if no node covers it,
 * or return NULL if pos is after the last range. Remember the found node,
 * to speed up subsequent searches for the same or similar positions (if
 * we return NULL, remember the last node.)
 */
    struct hilite_node*
hlist_find(anchor, pos)
    struct hilite_tree *anchor;
    POSITION pos;
{
    struct hilite_node *n, *m;

    if (anchor->lookaside)
    {
        int steps = 0;
        int hit = 0;

        n = anchor->lookaside;

        for (;;)
        {
            if (pos < n->r.hl_endpos)
            {
                if (n->prev == NULL || pos >= n->prev->r.hl_endpos)
                {
                    hit = 1;
                    break;
                }
            } else if (n->next == NULL)
            {
                n = NULL;
                hit = 1;
                break;
            }

            /*
             * If we don't find the right node within a small
             * distance, don't keep doing a linear search!
             */
            if (steps >= HILITE_LOOKASIDE_STEPS)
                break;
            steps++;

            if (pos < n->r.hl_endpos)
                anchor->lookaside = n = n->prev;
            else
                anchor->lookaside = n = n->next;
        }

        if (hit)
            return n;
    }

    n = anchor->root;
    m = NULL;

    while (n != NULL)
    {
        if (pos < n->r.hl_startpos)
        {
            if (n->left != NULL)
            {
                m = n;
                n = n->left;
                continue;
            }
            break;
        }
        if (pos >= n->r.hl_endpos)
        {
            if (n->right != NULL)
            {
                n = n->right;
                continue;
            }
            if (m != NULL)
            {
                n = m;
            } else
            {
                m = n;
                n = NULL;
            }
        }
        break;
    }

    if (n != NULL)
        anchor->lookaside = n;
    else if (m != NULL)
        anchor->lookaside = m;

    return n;
}

/*
 * Should any characters in a specified range be highlighted?
 */
    static int
is_hilited_range(pos, epos)
    POSITION pos;
    POSITION epos;
{
    struct hilite_node *n = hlist_find(&hilite_anchor, pos);
    return (n != NULL && (epos == NULL_POSITION || epos > n->r.hl_startpos));
}

/*
 * Is a line "filtered" -- that is, should it be hidden?
 */
    public int
is_filtered(pos)
    POSITION pos;
{
    struct hilite_node *n;

    if (ch_getflags() & CH_HELPFILE)
        return (0);

    n = hlist_find(&filter_anchor, pos);
    return (n != NULL && pos >= n->r.hl_startpos);
}

/*
 * If pos is hidden, return the next position which isn't, otherwise
 * just return pos.
 */
    public POSITION
next_unfiltered(pos)
    POSITION pos;
{
    struct hilite_node *n;

    if (ch_getflags() & CH_HELPFILE)
        return (pos);

    n = hlist_find(&filter_anchor, pos);
    while (n != NULL && pos >= n->r.hl_startpos)
    {
        pos = n->r.hl_endpos;
        n = n->next;
    }
    return (pos);
}

/*
 * If pos is hidden, return the previous position which isn't or 0 if
 * we're filtered right to the beginning, otherwise just return pos.
 */
    public POSITION
prev_unfiltered(pos)
    POSITION pos;
{
    struct hilite_node *n;

    if (ch_getflags() & CH_HELPFILE)
        return (pos);

    n = hlist_find(&filter_anchor, pos);
    while (n != NULL && pos >= n->r.hl_startpos)
    {
        pos = n->r.hl_startpos;
        if (pos == 0)
            break;
        pos--;
        n = n->prev;
    }
    return (pos);
}


/*
 * Should any characters in a specified range be highlighted?
 * If nohide is nonzero, don't consider hide_hilite.
 */
    public int
is_hilited_attr(pos, epos, nohide, p_matches)
    POSITION pos;
    POSITION epos;
    int nohide;
    int *p_matches;
{
    int match;

    if (p_matches != NULL)
        *p_matches = 0;

    if (!status_col &&
        start_attnpos != NULL_POSITION &&
        pos <= end_attnpos &&
         (epos == NULL_POSITION || epos >= start_attnpos))
        /*
         * The attn line overlaps this range.
         */
        return (AT_HILITE|AT_COLOR_ATTN);

    match = is_hilited_range(pos, epos);
    if (!match)
        return (0);

    if (p_matches == NULL)
        /*
         * Kinda kludgy way to recognize that caller is checking for
         * hilite in status column. In this case we want to return
         * hilite status even if hiliting is disabled or hidden.
         */
        return (AT_HILITE|AT_COLOR_SEARCH);

    /*
     * Report matches, even if we're hiding highlights.
     */
    *p_matches = 1;

    if (hilite_search == 0)
        /*
         * Not doing highlighting.
         */
        return (0);

    if (!nohide && hide_hilite)
        /*
         * Highlighting is hidden.
         */
        return (0);

    return (AT_HILITE|AT_COLOR_SEARCH);
}

/*
 * Tree node storage: get the current block of nodes if it has spare
 * capacity, or create a new one if not.
 */
    static struct hilite_storage*
hlist_getstorage(anchor)
    struct hilite_tree *anchor;
{
    int capacity = 1;
    struct hilite_storage *s;

    if (anchor->current)
    {
        if (anchor->current->used < anchor->current->capacity)
            return anchor->current;
        capacity = anchor->current->capacity * 2;
    }

    s = (struct hilite_storage *) ecalloc(1, sizeof(struct hilite_storage));
    s->nodes = (struct hilite_node *) ecalloc(capacity, sizeof(struct hilite_node));
    s->capacity = capacity;
    s->used = 0;
    s->next = NULL;
    if (anchor->current)
        anchor->current->next = s;
    else
        anchor->first = s;
    anchor->current = s;
    return s;
}

/*
 * Tree node storage: retrieve a new empty node to be inserted into the
 * tree.
 */
    static struct hilite_node*
hlist_getnode(anchor)
    struct hilite_tree *anchor;
{
    struct hilite_storage *s = hlist_getstorage(anchor);
    return &s->nodes[s->used++];
}

/*
 * Rotate the tree left around a pivot node.
 */
    static void
hlist_rotate_left(anchor, n)
    struct hilite_tree *anchor;
    struct hilite_node *n;
{
    struct hilite_node *np = n->parent;
    struct hilite_node *nr = n->right;
    struct hilite_node *nrl = n->right->left;

    if (np != NULL)
    {
        if (n == np->left)
            np->left = nr;
        else
            np->right = nr;
    } else
    {
        anchor->root = nr;
    }
    nr->left = n;
    n->right = nrl;

    nr->parent = np;
    n->parent = nr;
    if (nrl != NULL)
        nrl->parent = n;
}

/*
 * Rotate the tree right around a pivot node.
 */
    static void
hlist_rotate_right(anchor, n)
    struct hilite_tree *anchor;
    struct hilite_node *n;
{
    struct hilite_node *np = n->parent;
    struct hilite_node *nl = n->left;
    struct hilite_node *nlr = n->left->right;

    if (np != NULL)
    {
        if (n == np->right)
            np->right = nl;
        else
            np->left = nl;
    } else
    {
        anchor->root = nl;
    }
    nl->right = n;
    n->left = nlr;

    nl->parent = np;
    n->parent = nl;
    if (nlr != NULL)
        nlr->parent = n;
}


/*
 * Add a new hilite to a hilite list.
 */
    static void
add_hilite(anchor, hl)
    struct hilite_tree *anchor;
    struct hilite *hl;
{
    struct hilite_node *p, *n, *u;

    /* Ignore empty ranges. */
    if (hl->hl_startpos >= hl->hl_endpos)
        return;

    p = anchor->root;

    /* Inserting the very first node is trivial. */
    if (p == NULL)
    {
        n = hlist_getnode(anchor);
        n->r = *hl;
        anchor->root = n;
        anchor->lookaside = n;
        return;
    }

    /*
     * Find our insertion point. If we come across any overlapping
     * or adjoining existing ranges, shrink our range and discard
     * if it become empty.
     */
    for (;;)
    {
        if (hl->hl_startpos < p->r.hl_startpos)
        {
            if (hl->hl_endpos > p->r.hl_startpos)
                hl->hl_endpos = p->r.hl_startpos;
            if (p->left != NULL)
            {
                p = p->left;
                continue;
            }
            break;
        }
        if (hl->hl_startpos < p->r.hl_endpos) {
            hl->hl_startpos = p->r.hl_endpos;
            if (hl->hl_startpos >= hl->hl_endpos)
                return;
        }
        if (p->right != NULL)
        {
            p = p->right;
            continue;
        }
        break;
    }

    /*
     * Now we're at the right leaf, again check for contiguous ranges
     * and extend the existing node if possible to avoid the
     * insertion. Otherwise insert a new node at the leaf.
     */
    if (hl->hl_startpos < p->r.hl_startpos) {
        if (hl->hl_endpos == p->r.hl_startpos)
        {
            p->r.hl_startpos = hl->hl_startpos;
            return;
        }
        if (p->prev != NULL && p->prev->r.hl_endpos == hl->hl_startpos)
        {
            p->prev->r.hl_endpos = hl->hl_endpos;
            return;
        }

        p->left = n = hlist_getnode(anchor);
        n->next = p;
        if (p->prev != NULL)
        {
            n->prev = p->prev;
            p->prev->next = n;
        }
        p->prev = n;
    } else {
        if (p->r.hl_endpos == hl->hl_startpos)
        {
            p->r.hl_endpos = hl->hl_endpos;
            return;
        }
        if (p->next != NULL && hl->hl_endpos == p->next->r.hl_startpos) {
            p->next->r.hl_startpos = hl->hl_startpos;
            return;
        }

        p->right = n = hlist_getnode(anchor);
        n->prev = p;
        if (p->next != NULL)
        {
            n->next = p->next;
            p->next->prev = n;
        }
        p->next = n;
    }
    n->parent = p;
    n->red = 1;
    n->r = *hl;

    /*
     * The tree is in the correct order and covers the right ranges
     * now, but may have become unbalanced. Rebalance it using the
     * standard red-black tree constraints and operations.
     */
    for (;;)
    {
        /* case 1 - current is root, root is always black */
        if (n->parent == NULL)
        {
            n->red = 0;
            break;
        }

        /* case 2 - parent is black, we can always be red */
        if (!n->parent->red)
            break;

        /*
         * constraint: because the root must be black, if our
         * parent is red it cannot be the root therefore we must
         * have a grandparent
         */

        /*
         * case 3 - parent and uncle are red, repaint them black,
         * the grandparent red, and start again at the grandparent.
         */
        u = n->parent->parent->left;
        if (n->parent == u)
            u = n->parent->parent->right;
        if (u != NULL && u->red)
        {
            n->parent->red = 0;
            u->red = 0;
            n = n->parent->parent;
            n->red = 1;
            continue;
        }

        /*
         * case 4 - parent is red but uncle is black, parent and
         * grandparent on opposite sides. We need to start
         * changing the structure now. This and case 5 will shorten
         * our branch and lengthen the sibling, between them
         * restoring balance.
         */
        if (n == n->parent->right &&
            n->parent == n->parent->parent->left)
        {
            hlist_rotate_left(anchor, n->parent);
            n = n->left;
        } else if (n == n->parent->left &&
               n->parent == n->parent->parent->right)
        {
            hlist_rotate_right(anchor, n->parent);
            n = n->right;
        }

        /*
         * case 5 - parent is red but uncle is black, parent and
         * grandparent on same side
         */
        n->parent->red = 0;
        n->parent->parent->red = 1;
        if (n == n->parent->left)
            hlist_rotate_right(anchor, n->parent->parent);
        else
            hlist_rotate_left(anchor, n->parent->parent);
        break;
    }
}

/*
 * Highlight every character in a range of displayed characters.
 */
    static void
create_hilites(linepos, start_index, end_index, chpos)
    POSITION linepos;
    int start_index;
    int end_index;
    int *chpos;
{
    struct hilite hl;
    int i;

    /* Start the first hilite. */
    hl.hl_startpos = linepos + chpos[start_index];

    /*
     * Step through the displayed chars.
     * If the source position (before cvt) of the char is one more
     * than the source pos of the previous char (the usual case),
     * just increase the size of the current hilite by one.
     * Otherwise (there are backspaces or something involved),
     * finish the current hilite and start a new one.
     */
    for (i = start_index+1;  i <= end_index;  i++)
    {
        if (chpos[i] != chpos[i-1] + 1 || i == end_index)
        {
            hl.hl_endpos = linepos + chpos[i-1] + 1;
            add_hilite(&hilite_anchor, &hl);
            /* Start new hilite unless this is the last char. */
            if (i < end_index)
            {
                hl.hl_startpos = linepos + chpos[i];
            }
        }
    }
}

/*
 * Make a hilite for each string in a physical line which matches
 * the current pattern.
 * sp,ep delimit the first match already found.
 */
    static void
hilite_line(linepos, line, line_len, chpos, sp, ep, cvt_ops)
    POSITION linepos;
    char *line;
    int line_len;
    int *chpos;
    char *sp;
    char *ep;
    int cvt_ops;
{
    char *searchp;
    char *line_end = line + line_len;

    /*
     * sp and ep delimit the first match in the line.
     * Mark the corresponding file positions, then
     * look for further matches and mark them.
     * {{ This technique, of calling match_pattern on subsequent
     *    substrings of the line, may mark more than is correct
     *    if the pattern starts with "^".  This bug is fixed
     *    for those regex functions that accept a notbol parameter
     *    (currently POSIX, PCRE and V8-with-regexec2). }}
     */
    searchp = line;
    do {
        if (sp == NULL || ep == NULL)
            return;
        create_hilites(linepos, sp-line, ep-line, chpos);
        /*
         * If we matched more than zero characters,
         * move to the first char after the string we matched.
         * If we matched zero, just move to the next char.
         */
        if (ep > searchp)
            searchp = ep;
        else if (searchp != line_end)
            searchp++;
        else /* end of line */
            break;
    } while (match_pattern(info_compiled(&search_info), search_info.text,
            searchp, line_end - searchp, &sp, &ep, 1, search_info.search_type));
}
#endif

#if HILITE_SEARCH
/*
 * Find matching text which is currently on screen and highlight it.
 */
    static void
hilite_screen(VOID_PARAM)
{
    struct scrpos scrpos;

    get_scrpos(&scrpos, TOP);
    if (scrpos.pos == NULL_POSITION)
        return;
    prep_hilite(scrpos.pos, position(BOTTOM_PLUS_ONE), -1);
    repaint_hilite(1);
}

/*
 * Change highlighting parameters.
 */
    public void
chg_hilite(VOID_PARAM)
{
    /*
     * Erase any highlights currently on screen.
     */
    clr_hilite();
    hide_hilite = 0;

    if (hilite_search == OPT_ONPLUS)
        /*
         * Display highlights.
         */
        hilite_screen();
}
#endif

/*
 * Figure out where to start a search.
 */
    static POSITION
search_pos(search_type)
    int search_type;
{
    POSITION pos;
    int sindex;

    if (empty_screen())
    {
        /*
         * Start at the beginning (or end) of the file.
         * The empty_screen() case is mainly for
         * command line initiated searches;
         * for example, "+/xyz" on the command line.
         * Also for multi-file (SRCH_PAST_EOF) searches.
         */
        if (search_type & SRCH_FORW)
        {
            pos = ch_zero();
        } else
        {
            pos = ch_length();
            if (pos == NULL_POSITION)
            {
                (void) ch_end_seek();
                pos = ch_length();
            }
        }
        sindex = 0;
    } else
    {
        int add_one = 0;

        if (how_search == OPT_ON)
        {
            /*
             * Search does not include current screen.
             */
            if (search_type & SRCH_FORW)
                sindex = sc_height-1; /* BOTTOM_PLUS_ONE */
            else
                sindex = 0; /* TOP */
        } else if (how_search == OPT_ONPLUS && !(search_type & SRCH_AFTER_TARGET))
        {
            /*
             * Search includes all of displayed screen.
             */
            if (search_type & SRCH_FORW)
                sindex = 0; /* TOP */
            else
                sindex = sc_height-1; /* BOTTOM_PLUS_ONE */
        } else
        {
            /*
             * Search includes the part of current screen beyond the jump target.
             * It starts at the jump target (if searching backwards),
             * or at the jump target plus one (if forwards).
             */
            sindex = sindex_from_sline(jump_sline);
            if (search_type & SRCH_FORW)
                add_one = 1;
        }
        pos = position(sindex);
        if (add_one)
            pos = forw_raw_line(pos, (char **)NULL, (int *)NULL);
    }

    /*
     * If the line is empty, look around for a plausible starting place.
     */
    if (search_type & SRCH_FORW)
    {
        while (pos == NULL_POSITION)
        {
            if (++sindex >= sc_height)
                break;
            pos = position(sindex);
        }
    } else
    {
        while (pos == NULL_POSITION)
        {
            if (--sindex < 0)
                break;
            pos = position(sindex);
        }
    }
    return (pos);
}

/*
 * Check to see if the line matches the filter pattern.
 * If so, add an entry to the filter list.
 */
#if HILITE_SEARCH
    static int
matches_filters(pos, cline, line_len, chpos, linepos, sp, ep)
    POSITION pos;
    char *cline;
    int line_len;
    int *chpos;
    POSITION linepos;
    char **sp;
    char **ep;
{
    struct pattern_info *filter;

    for (filter = filter_infos; filter != NULL; filter = filter->next)
    {
        int line_filter = match_pattern(info_compiled(filter), filter->text,
            cline, line_len, sp, ep, 0, filter->search_type);
        if (line_filter)
        {
            struct hilite hl;
            hl.hl_startpos = linepos;
            hl.hl_endpos = pos;
            add_hilite(&filter_anchor, &hl);
            free(cline);
            free(chpos);
            return (1);
        }
    }
    return (0);
}
#endif

/*
 * Get the position of the first char in the screen line which
 * puts tpos on screen.
 */
    static POSITION
get_lastlinepos(pos, tpos, sheight)
    POSITION pos;
    POSITION tpos;
    int sheight;
{
    int nlines;

    for (nlines = 0;;  nlines++)
    {
        POSITION npos = forw_line(pos);
        if (npos > tpos)
        {
            if (nlines < sheight)
                return NULL_POSITION;
            return pos;
        }
        pos = npos;
    }
}

/*
 * Get the segment index of tpos in the line starting at pos.
 * A segment is a string of printable chars that fills the screen width.
 */
    static int
get_seg(pos, tpos)
    POSITION pos;
    POSITION tpos;
{
    int seg;

    for (seg = 0;;  seg++)
    {
        POSITION npos = forw_line_seg(pos, FALSE, FALSE, TRUE);
        if (npos > tpos)
            return seg;
        pos = npos;
    }
}

/*
 * Search a subset of the file, specified by start/end position.
 */
    static int
search_range(pos, endpos, search_type, matches, maxlines, plinepos, pendpos, plastlinepos)
    POSITION pos;
    POSITION endpos;
    int search_type;
    int matches;
    int maxlines;
    POSITION *plinepos;
    POSITION *pendpos;
    POSITION *plastlinepos;
{
    char *line;
    char *cline;
    int line_len;
    LINENUM linenum;
    char *sp, *ep;
    int line_match;
    int cvt_ops;
    size_t cvt_len;
    int *chpos;
    POSITION linepos, oldpos;
    int swidth = sc_width - line_pfx_width();
    int sheight = sc_height - sindex_from_sline(jump_sline);

    linenum = find_linenum(pos);
    oldpos = pos;
    /* When the search wraps around, end at starting position. */
    if ((search_type & SRCH_WRAP) && endpos == NULL_POSITION)
        endpos = pos;
    for (;;)
    {
        /*
         * Get lines until we find a matching one or until
         * we hit end-of-file (or beginning-of-file if we're
         * going backwards), or until we hit the end position.
         */
        if (ABORT_SIGS())
        {
            /*
             * A signal aborts the search.
             */
            return (-1);
        }

        if ((endpos != NULL_POSITION && !(search_type & SRCH_WRAP) &&
            (((search_type & SRCH_FORW) && pos >= endpos) ||
             ((search_type & SRCH_BACK) && pos <= endpos))) || maxlines == 0)
        {
            /*
             * Reached end position without a match.
             */
            if (pendpos != NULL)
                *pendpos = pos;
            return (matches);
        }
        if (maxlines > 0)
            maxlines--;

        if (search_type & SRCH_FORW)
        {
            /*
             * Read the next line, and save the
             * starting position of that line in linepos.
             */
            linepos = pos;
            pos = forw_raw_line(pos, &line, &line_len);
            if (linenum != 0)
                linenum++;
        } else
        {
            /*
             * Read the previous line and save the
             * starting position of that line in linepos.
             */
            pos = back_raw_line(pos, &line, &line_len);
            linepos = pos;
            if (linenum != 0)
                linenum--;
        }

        if (pos == NULL_POSITION)
        {
            /*
             * Reached EOF/BOF without a match.
             */
            if (search_type & SRCH_WRAP)
            {
                /*
                 * The search wraps around the current file, so
                 * try to continue at BOF/EOF.
                 */
                if (search_type & SRCH_FORW)
                {
                    pos = ch_zero();
                } else
                {
                    pos = ch_length();
                    if (pos == NULL_POSITION)
                    {
                        (void) ch_end_seek();
                        pos = ch_length();
                    }
                }
                if (pos != NULL_POSITION) {
                    /*
                     * Wrap-around was successful. Clear
                     * the flag so we don't wrap again, and
                     * continue the search at new pos.
                     */
                    search_type &= ~SRCH_WRAP;
                    linenum = find_linenum(pos);
                    continue;
                }
            }
            if (pendpos != NULL)
                *pendpos = oldpos;
            return (matches);
        }

        /*
         * If we're using line numbers, we might as well
         * remember the information we have now (the position
         * and line number of the current line).
         * Don't do it for every line because it slows down
         * the search.  Remember the line number only if
         * we're "far" from the last place we remembered it.
         */
        if (linenums && abs((int)(pos - oldpos)) > 2048)
            add_lnum(linenum, pos);
        oldpos = pos;

#if HILITE_SEARCH
        if (is_filtered(linepos))
            continue;
#endif

        /*
         * If it's a caseless search, convert the line to lowercase.
         * If we're doing backspace processing, delete backspaces.
         */
        cvt_ops = get_cvt_ops();
        cvt_len = cvt_length(line_len, cvt_ops);
        cline = (char *) ecalloc(1, cvt_len);
        chpos = cvt_alloc_chpos(cvt_len);
        cvt_text(cline, line, chpos, &line_len, cvt_ops);

#if HILITE_SEARCH
        /*
         * If any filters are in effect, ignore non-matching lines.
         */
        if (filter_infos != NULL &&
           ((search_type & SRCH_FIND_ALL) ||
             prep_startpos == NULL_POSITION ||
             linepos < prep_startpos || linepos >= prep_endpos)) {
            if (matches_filters(pos, cline, line_len, chpos, linepos, &sp, &ep))
                continue;
        }
#endif

        /*
         * Test the next line to see if we have a match.
         * We are successful if we either want a match and got one,
         * or if we want a non-match and got one.
         */
        if (prev_pattern(&search_info))
        {
            line_match = match_pattern(info_compiled(&search_info), search_info.text,
                cline, line_len, &sp, &ep, 0, search_type);
            if (line_match)
            {
                /*
                 * Got a match.
                 */
                if (search_type & SRCH_FIND_ALL)
                {
#if HILITE_SEARCH
                    /*
                     * We are supposed to find all matches in the range.
                     * Just add the matches in this line to the
                     * hilite list and keep searching.
                     */
                    hilite_line(linepos, cline, line_len, chpos, sp, ep, cvt_ops);
#endif
                } else if (--matches <= 0)
                {
                    /*
                     * Found the one match we're looking for.
                     * Return it.
                     */
#if HILITE_SEARCH
                    if (hilite_search == OPT_ON)
                    {
                        /*
                         * Clear the hilite list and add only
                         * the matches in this one line.
                         */
                        clr_hilite();
                        hilite_line(linepos, cline, line_len, chpos, sp, ep, cvt_ops);
                    }
#endif
                    if (chop_line())
                    {
                        /*
                         * If necessary, shift horizontally to make sure
                         * search match is fully visible.
                         */
                        if (sp != NULL && ep != NULL)
                        {
                            POSITION start_off = (POSITION)(sp - cline);
                            POSITION end_off = (POSITION)(ep - cline);
                            int save_hshift = hshift;
                            int sshift;
                            int eshift;
                            hshift = 0; /* make get_seg count screen lines */
                            sshift = swidth * get_seg(linepos, linepos + chpos[start_off]);
                            eshift = swidth * get_seg(linepos, linepos + chpos[end_off]);
                            if (sshift >= save_hshift && eshift <= save_hshift)
                            {
                                hshift = save_hshift;
                            } else
                            {
                                hshift = sshift;
                                screen_trashed = 1;
                            }
                        }
                    } else if (plastlinepos != NULL)
                    {
                        /*
                         * If the line is so long that the highlighted match
                         * won't be seen when the line is displayed normally
                         * (starting at the first char) because it fills the whole
                         * screen and more, scroll forward until the last char
                         * of the match appears in the last line on the screen.
                         * lastlinepos is the position of the first char of that last line.
                         */
                        if (ep != NULL)
                        {
                            POSITION end_off = (POSITION)(ep - cline);
                            if (end_off >= swidth * sheight / 4) /* heuristic */
                                *plastlinepos = get_lastlinepos(linepos, linepos + chpos[end_off], sheight);
                        }
                    }
                    free(cline);
                    free(chpos);
                    if (plinepos != NULL)
                        *plinepos = linepos;
                    return (0);
                }
            }
        }
        free(cline);
        free(chpos);
    }
}

/*
 * search for a pattern in history. If found, compile that pattern.
 */
    static int
hist_pattern(search_type)
    int search_type;
{
#if CMD_HISTORY
    char *pattern;

    set_mlist(ml_search, 0);
    pattern = cmd_lastpattern();
    if (pattern == NULL)
        return (0);

    if (set_pattern(&search_info, pattern, search_type, 1) < 0)
        return (-1);

#if HILITE_SEARCH
    if (hilite_search == OPT_ONPLUS && !hide_hilite)
        hilite_screen();
#endif

    return (1);
#else /* CMD_HISTORY */
    return (0);
#endif /* CMD_HISTORY */
}

/*
 * Change the caseless-ness of searches.
 * Updates the internal search state to reflect a change in the -i flag.
 */
    public void
chg_caseless(VOID_PARAM)
{
    if (!is_ucase_pattern)
    {
        /*
         * Pattern did not have uppercase.
         * Set the search caselessness to the global caselessness.
         */
        is_caseless = caseless;
        /*
         * If regex handles caseless, we need to discard
         * the pattern which was compiled with the old caseless.
         */
        if (!re_handles_caseless)
            /* We handle caseless, so the pattern doesn't change. */
            return;
    }
    /*
     * Regenerate the pattern using the new state.
     */
    clear_pattern(&search_info);
    (void) hist_pattern(search_info.search_type);
}

/*
 * Search for the n-th occurrence of a specified pattern,
 * either forward or backward.
 * Return the number of matches not yet found in this file
 * (that is, n minus the number of matches found).
 * Return -1 if the search should be aborted.
 * Caller may continue the search in another file
 * if less than n matches are found in this file.
 */
    public int
search(search_type, pattern, n)
    int search_type;
    char *pattern;
    int n;
{
    POSITION pos;
    POSITION opos;
    POSITION lastlinepos = NULL_POSITION;

    if (pattern == NULL || *pattern == '\0')
    {
        /*
         * A null pattern means use the previously compiled pattern.
         */
        search_type |= SRCH_AFTER_TARGET;
        if (!prev_pattern(&search_info))
        {
            int r = hist_pattern(search_type);
            if (r == 0)
                error("No previous regular expression", NULL_PARG);
            if (r <= 0)
                return (-1);
        }
        if ((search_type & SRCH_NO_REGEX) !=
              (search_info.search_type & SRCH_NO_REGEX))
        {
            error("Please re-enter search pattern", NULL_PARG);
            return -1;
        }
#if HILITE_SEARCH
        if (hilite_search == OPT_ON || status_col)
        {
            /*
             * Erase the highlights currently on screen.
             * If the search fails, we'll redisplay them later.
             */
            repaint_hilite(0);
        }
        if (hilite_search == OPT_ONPLUS && hide_hilite)
        {
            /*
             * Highlight any matches currently on screen,
             * before we actually start the search.
             */
            hide_hilite = 0;
            hilite_screen();
        }
        hide_hilite = 0;
#endif
    } else
    {
        /*
         * Compile the pattern.
         */
        int show_error = !(search_type & SRCH_INCR);
        if (set_pattern(&search_info, pattern, search_type, show_error) < 0)
            return (-1);
#if HILITE_SEARCH
        if (hilite_search || status_col)
        {
            /*
             * Erase the highlights currently on screen.
             * Also permanently delete them from the hilite list.
             */
            repaint_hilite(0);
            hide_hilite = 0;
            clr_hilite();
        }
        if (hilite_search == OPT_ONPLUS || status_col)
        {
            /*
             * Highlight any matches currently on screen,
             * before we actually start the search.
             */
            hilite_screen();
        }
#endif
    }

    /*
     * Figure out where to start the search.
     */
    pos = search_pos(search_type);
    opos = position(sindex_from_sline(jump_sline));
    if (pos == NULL_POSITION)
    {
        /*
         * Can't find anyplace to start searching from.
         */
        if (search_type & SRCH_PAST_EOF)
            return (n);
#if HILITE_SEARCH
        if (hilite_search == OPT_ON || status_col)
            repaint_hilite(1);
#endif
        error("Nothing to search", NULL_PARG);
        return (-1);
    }

    n = search_range(pos, NULL_POSITION, search_type, n, -1,
            &pos, (POSITION*)NULL, &lastlinepos);
    if (n != 0)
    {
        /*
         * Search was unsuccessful.
         */
#if HILITE_SEARCH
        if ((hilite_search == OPT_ON || status_col) && n > 0)
            /*
             * Redisplay old hilites.
             */
            repaint_hilite(1);
#endif
        return (n);
    }

    if (!(search_type & SRCH_NO_MOVE))
    {
        /*
         * Go to the matching line.
         */
        if (lastlinepos != NULL_POSITION)
            jump_loc(lastlinepos, BOTTOM);
        else if (pos != opos)
            jump_loc(pos, jump_sline);
    }

#if HILITE_SEARCH
    if (hilite_search == OPT_ON || status_col)
        /*
         * Display new hilites in the matching line.
         */
        repaint_hilite(1);
#endif
    return (0);
}

#if HILITE_SEARCH
/*
 * Prepare hilites in a given range of the file.
 *
 * The pair (prep_startpos,prep_endpos) delimits a contiguous region
 * of the file that has been "prepared"; that is, scanned for matches for
 * the current search pattern, and hilites have been created for such matches.
 * If prep_startpos == NULL_POSITION, the prep region is empty.
 * If prep_endpos == NULL_POSITION, the prep region extends to EOF.
 * prep_hilite asks that the range (spos,epos) be covered by the prep region.
 */
    public void
prep_hilite(spos, epos, maxlines)
    POSITION spos;
    POSITION epos;
    int maxlines;
{
    POSITION nprep_startpos = prep_startpos;
    POSITION nprep_endpos = prep_endpos;
    POSITION new_epos;
    POSITION max_epos;
    int result;
    int i;

/*
 * Search beyond where we're asked to search, so the prep region covers
 * more than we need.  Do one big search instead of a bunch of small ones.
 */
#define SEARCH_MORE (3*size_linebuf)

    if (!prev_pattern(&search_info) && !is_filtering())
        return;

    /*
     * Make sure our prep region always starts at the beginning of
     * a line. (search_range takes care of the end boundary below.)
     */
    spos = back_raw_line(spos+1, (char **)NULL, (int *)NULL);

    /*
     * If we're limited to a max number of lines, figure out the
     * file position we should stop at.
     */
    if (maxlines < 0)
        max_epos = NULL_POSITION;
    else
    {
        max_epos = spos;
        for (i = 0;  i < maxlines;  i++)
            max_epos = forw_raw_line(max_epos, (char **)NULL, (int *)NULL);
    }

    /*
     * Find two ranges:
     * The range that we need to search (spos,epos); and the range that
     * the "prep" region will then cover (nprep_startpos,nprep_endpos).
     */

    if (prep_startpos == NULL_POSITION ||
        (epos != NULL_POSITION && epos < prep_startpos) ||
        spos > prep_endpos)
    {
        /*
         * New range is not contiguous with old prep region.
         * Discard the old prep region and start a new one.
         */
        clr_hilite();
        clr_filter();
        if (epos != NULL_POSITION)
            epos += SEARCH_MORE;
        nprep_startpos = spos;
    } else
    {
        /*
         * New range partially or completely overlaps old prep region.
         */
        if (epos == NULL_POSITION)
        {
            /*
             * New range goes to end of file.
             */
            ;
        } else if (epos > prep_endpos)
        {
            /*
             * New range ends after old prep region.
             * Extend prep region to end at end of new range.
             */
            epos += SEARCH_MORE;
        } else /* (epos <= prep_endpos) */
        {
            /*
             * New range ends within old prep region.
             * Truncate search to end at start of old prep region.
             */
            epos = prep_startpos;
        }

        if (spos < prep_startpos)
        {
            /*
             * New range starts before old prep region.
             * Extend old prep region backwards to start at
             * start of new range.
             */
            if (spos < SEARCH_MORE)
                spos = 0;
            else
                spos -= SEARCH_MORE;
            nprep_startpos = spos;
        } else /* (spos >= prep_startpos) */
        {
            /*
             * New range starts within or after old prep region.
             * Trim search to start at end of old prep region.
             */
            spos = prep_endpos;
        }
    }

    if (epos != NULL_POSITION && max_epos != NULL_POSITION &&
        epos > max_epos)
        /*
         * Don't go past the max position we're allowed.
         */
        epos = max_epos;

    if (epos == NULL_POSITION || epos > spos)
    {
        int search_type = SRCH_FORW | SRCH_FIND_ALL;
        search_type |= (search_info.search_type & SRCH_NO_REGEX);
        for (;;)
        {
            result = search_range(spos, epos, search_type, 0, maxlines, (POSITION*)NULL, &new_epos, (POSITION*)NULL);
            if (result < 0)
                return;
            if (prep_endpos == NULL_POSITION || new_epos > prep_endpos)
                nprep_endpos = new_epos;

            /*
             * Check both ends of the resulting prep region to
             * make sure they're not filtered. If they are,
             * keep going at least one more line until we find
             * something that isn't filtered, or hit the end.
             */
            if (prep_endpos == NULL_POSITION || nprep_endpos > prep_endpos)
            {
                if (new_epos >= nprep_endpos && is_filtered(new_epos-1))
                {
                    spos = nprep_endpos;
                    epos = forw_raw_line(nprep_endpos, (char **)NULL, (int *)NULL);
                    if (epos == NULL_POSITION)
                        break;
                    maxlines = 1;
                    continue;
                }
            }

            if (prep_startpos == NULL_POSITION || nprep_startpos < prep_startpos)
            {
                if (nprep_startpos > 0 && is_filtered(nprep_startpos))
                {
                    epos = nprep_startpos;
                    spos = back_raw_line(nprep_startpos, (char **)NULL, (int *)NULL);
                    if (spos == NULL_POSITION)
                        break;
                    nprep_startpos = spos;
                    maxlines = 1;
                    continue;
                }
            }
            break;
        }
    }
    prep_startpos = nprep_startpos;
    prep_endpos = nprep_endpos;
}

/*
 * Set the pattern to be used for line filtering.
 */
    public void
set_filter_pattern(pattern, search_type)
    char *pattern;
    int search_type;
{
    struct pattern_info *filter;

    clr_filter();
    if (pattern == NULL || *pattern == '\0')
    {
        /* Clear and free all filters. */
        for (filter = filter_infos; filter != NULL; )
        {
            struct pattern_info *next_filter = filter->next;
            clear_pattern(filter);
            free(filter);
            filter = next_filter;
        }
        filter_infos = NULL;
    } else
    {
        /* Create a new filter and add it to the filter_infos list. */
        filter = ecalloc(1, sizeof(struct pattern_info));
        init_pattern(filter);
        if (set_pattern(filter, pattern, search_type, 1) < 0)
        {
            free(filter);
            return;
        }
        filter->next = filter_infos;
        filter_infos = filter;
    }
    screen_trashed = 1;
}

/*
 * Is there a line filter in effect?
 */
    public int
is_filtering(VOID_PARAM)
{
    if (ch_getflags() & CH_HELPFILE)
        return (0);
    return (filter_infos != NULL);
}
#endif

#if HAVE_V8_REGCOMP
/*
 * This function is called by the V8 regcomp to report
 * errors in regular expressions.
 */
public int reg_show_error = 1;

    void
regerror(s)
    char *s;
{
    PARG parg;

    if (!reg_show_error)
        return;
    parg.p_string = s;
    error("%s", &parg);
}
#endif