contrib/less/line.c

/*
 * Copyright (C) 1984-2017  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 manipulate the "line buffer".
 * The line buffer holds a line of output as it is being built
 * in preparation for output to the screen.
 */

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

#if MSDOS_COMPILER==WIN32C
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#endif

static char *linebuf = NULL;	/* Buffer which holds the current output line */
static char *attr = NULL;	/* Extension of linebuf to hold attributes */
public int size_linebuf = 0;	/* Size of line buffer (and attr buffer) */

static int cshift;		/* Current left-shift of output line buffer */
public int hshift;		/* Desired left-shift of output line buffer */
public int tabstops[TABSTOP_MAX] = { 0 }; /* Custom tabstops */
public int ntabstops = 1;	/* Number of tabstops */
public int tabdefault = 8;	/* Default repeated tabstops */
public POSITION highest_hilite;	/* Pos of last hilite in file found so far */

static int curr;		/* Index into linebuf */
static int column;		/* Printable length, accounting for
				   backspaces, etc. */
static int right_curr;
static int right_column;
static int overstrike;		/* Next char should overstrike previous char */
static int last_overstrike = AT_NORMAL;
static int is_null_line;	/* There is no current line */
static int lmargin;		/* Left margin */
static LWCHAR pendc;
static POSITION pendpos;
static char *end_ansi_chars;
static char *mid_ansi_chars;

static int attr_swidth LESSPARAMS ((int a));
static int attr_ewidth LESSPARAMS ((int a));
static int do_append LESSPARAMS ((LWCHAR ch, char *rep, POSITION pos));

extern int sigs;
extern int bs_mode;
extern int linenums;
extern int ctldisp;
extern int twiddle;
extern int binattr;
extern int status_col;
extern int auto_wrap, ignaw;
extern int bo_s_width, bo_e_width;
extern int ul_s_width, ul_e_width;
extern int bl_s_width, bl_e_width;
extern int so_s_width, so_e_width;
extern int sc_width, sc_height;
extern int utf_mode;
extern POSITION start_attnpos;
extern POSITION end_attnpos;
extern LWCHAR rscroll_char;
extern int rscroll_attr;

static char mbc_buf[MAX_UTF_CHAR_LEN];
static int mbc_buf_len = 0;
static int mbc_buf_index = 0;
static POSITION mbc_pos;

/*
 * Initialize from environment variables.
 */
	public void
init_line()
{
	end_ansi_chars = lgetenv("LESSANSIENDCHARS");
	if (end_ansi_chars == NULL || *end_ansi_chars == '\0')
		end_ansi_chars = "m";

	mid_ansi_chars = lgetenv("LESSANSIMIDCHARS");
	if (mid_ansi_chars == NULL || *mid_ansi_chars == '\0')
		mid_ansi_chars = "0123456789:;[?!\"'#%()*+ ";

	linebuf = (char *) ecalloc(LINEBUF_SIZE, sizeof(char));
	attr = (char *) ecalloc(LINEBUF_SIZE, sizeof(char));
	size_linebuf = LINEBUF_SIZE;
}

/*
 * Expand the line buffer.
 */
	static int
expand_linebuf()
{
	/* Double the size of the line buffer. */
	int new_size = size_linebuf * 2;

	/* Just realloc to expand the buffer, if we can. */
#if HAVE_REALLOC
	char *new_buf = (char *) realloc(linebuf, new_size);
	char *new_attr = (char *) realloc(attr, new_size);
#else
	char *new_buf = (char *) calloc(new_size, sizeof(char));
	char *new_attr = (char *) calloc(new_size, sizeof(char));
#endif
	if (new_buf == NULL || new_attr == NULL)
	{
		if (new_attr != NULL)
			free(new_attr);
		if (new_buf != NULL)
			free(new_buf);
		return 1;
	}
#if HAVE_REALLOC
	/*
	 * We realloc'd the buffers; they already have the old contents.
	 */
	#if 0
	memset(new_buf + size_linebuf, 0, new_size - size_linebuf);
	memset(new_attr + size_linebuf, 0, new_size - size_linebuf);
	#endif
#else
	/*
	 * We just calloc'd the buffers; copy the old contents.
	 */
	memcpy(new_buf, linebuf, size_linebuf * sizeof(char));
	memcpy(new_attr, attr, size_linebuf * sizeof(char));
	free(attr);
	free(linebuf);
#endif
	linebuf = new_buf;
	attr = new_attr;
	size_linebuf = new_size;
	return 0;
}

/*
 * Is a character ASCII?
 */
	public int
is_ascii_char(ch)
	LWCHAR ch;
{
	return (ch <= 0x7F);
}

/*
 * Rewind the line buffer.
 */
	public void
prewind()
{
	curr = 0;
	column = 0;
	right_curr = 0;
	right_column = 0;
	cshift = 0;
	overstrike = 0;
	last_overstrike = AT_NORMAL;
	mbc_buf_len = 0;
	is_null_line = 0;
	pendc = '\0';
	lmargin = 0;
	if (status_col)
		lmargin += 2;
}

/*
 * Set a character in the line buffer.
 */
	static void
set_linebuf(n, ch, a)
	int n;
	LWCHAR ch;
	char a;
{
	linebuf[n] = ch;
	attr[n] = a;
}

/*
 * Append a character to the line buffer.
 */
	static void
add_linebuf(ch, a, w)
	LWCHAR ch;
	char a;
	int w;
{
	set_linebuf(curr++, ch, a);
	column += w;
}

/*
 * Insert the line number (of the given position) into the line buffer.
 */
	public void
plinenum(pos)
	POSITION pos;
{
	LINENUM linenum = 0;
	int i;

	if (linenums == OPT_ONPLUS)
	{
		/*
		 * Get the line number and put it in the current line.
		 * {{ Note: since find_linenum calls forw_raw_line,
		 *    it may seek in the input file, requiring the caller
		 *    of plinenum to re-seek if necessary. }}
		 * {{ Since forw_raw_line modifies linebuf, we must
		 *    do this first, before storing anything in linebuf. }}
		 */
		linenum = find_linenum(pos);
	}

	/*
	 * Display a status column if the -J option is set.
	 */
	if (status_col)
	{
		int a = AT_NORMAL;
		char c = posmark(pos);
		if (c != 0)
			a |= AT_HILITE;
		else
		{
			c = ' ';
			if (start_attnpos != NULL_POSITION &&
			    pos >= start_attnpos && pos <= end_attnpos)
				a |= AT_HILITE;
		}
		add_linebuf(c, a, 1); /* column 0: status */
		add_linebuf(' ', AT_NORMAL, 1); /* column 1: empty */
	}

	/*
	 * Display the line number at the start of each line
	 * if the -N option is set.
	 */
	if (linenums == OPT_ONPLUS)
	{
		char buf[INT_STRLEN_BOUND(linenum) + 2];
		int pad = 0;
		int n;

		linenumtoa(linenum, buf);
		n = (int) strlen(buf);
		if (n < MIN_LINENUM_WIDTH)
			pad = MIN_LINENUM_WIDTH - n;
		for (i = 0; i < pad; i++)
			add_linebuf(' ', AT_NORMAL, 1);
		for (i = 0; i < n; i++)
			add_linebuf(buf[i], AT_BOLD, 1);
		add_linebuf(' ', AT_NORMAL, 1);
		lmargin += n + pad + 1;
	}
	/*
	 * Append enough spaces to bring us to the lmargin.
	 */
	while (column < lmargin)
	{
		add_linebuf(' ', AT_NORMAL, 1);
	}
}

/*
 * Shift the input line left.
 * This means discarding N printable chars at the start of the buffer.
 */
	static void
pshift(shift)
	int shift;
{
	LWCHAR prev_ch = 0;
	unsigned char c;
	int shifted = 0;
	int to;
	int from;
	int len;
	int width;
	int prev_attr;
	int next_attr;

	if (shift > column - lmargin)
		shift = column - lmargin;
	if (shift > curr - lmargin)
		shift = curr - lmargin;

	to = from = lmargin;
	/*
	 * We keep on going when shifted == shift
	 * to get all combining chars.
	 */
	while (shifted <= shift && from < curr)
	{
		c = linebuf[from];
		if (ctldisp == OPT_ONPLUS && IS_CSI_START(c))
		{
			/* Keep cumulative effect.  */
			linebuf[to] = c;
			attr[to++] = attr[from++];
			while (from < curr && linebuf[from])
			{
				linebuf[to] = linebuf[from];
				attr[to++] = attr[from];
				if (!is_ansi_middle(linebuf[from++]))
					break;
			}
			continue;
		}

		width = 0;

		if (!IS_ASCII_OCTET(c) && utf_mode)
		{
			/* Assumes well-formedness validation already done.  */
			LWCHAR ch;

			len = utf_len(c);
			if (from + len > curr)
				break;
			ch = get_wchar(linebuf + from);
			if (!is_composing_char(ch) && !is_combining_char(prev_ch, ch))
				width = is_wide_char(ch) ? 2 : 1;
			prev_ch = ch;
		} else
		{
			len = 1;
			if (c == '\b')
				/* XXX - Incorrect if several '\b' in a row.  */
				width = (utf_mode && is_wide_char(prev_ch)) ? -2 : -1;
			else if (!control_char(c))
				width = 1;
			prev_ch = 0;
		}

		if (width == 2 && shift - shifted == 1) {
			/* Should never happen when called by pshift_all().  */
			attr[to] = attr[from];
			/*
			 * Assume a wide_char will never be the first half of a
			 * combining_char pair, so reset prev_ch in case we're
			 * followed by a '\b'.
			 */
			prev_ch = linebuf[to++] = ' ';
			from += len;
			shifted++;
			continue;
		}

		/* Adjust width for magic cookies. */
		prev_attr = (to > 0) ? attr[to-1] : AT_NORMAL;
		next_attr = (from + len < curr) ? attr[from + len] : prev_attr;
		if (!is_at_equiv(attr[from], prev_attr) &&
			!is_at_equiv(attr[from], next_attr))
		{
			width += attr_swidth(attr[from]);
			if (from + len < curr)
				width += attr_ewidth(attr[from]);
			if (is_at_equiv(prev_attr, next_attr))
			{
				width += attr_ewidth(prev_attr);
				if (from + len < curr)
					width += attr_swidth(next_attr);
			}
		}

		if (shift - shifted < width)
			break;
		from += len;
		shifted += width;
		if (shifted < 0)
			shifted = 0;
	}
	while (from < curr)
	{
		linebuf[to] = linebuf[from];
		attr[to++] = attr[from++];
	}
	curr = to;
	column -= shifted;
	cshift += shifted;
}

/*
 *
 */
	public void
pshift_all()
{
	pshift(column);
}

/*
 * Return the printing width of the start (enter) sequence
 * for a given character attribute.
 */
	static int
attr_swidth(a)
	int a;
{
	int w = 0;

	a = apply_at_specials(a);

	if (a & AT_UNDERLINE)
		w += ul_s_width;
	if (a & AT_BOLD)
		w += bo_s_width;
	if (a & AT_BLINK)
		w += bl_s_width;
	if (a & AT_STANDOUT)
		w += so_s_width;

	return w;
}

/*
 * Return the printing width of the end (exit) sequence
 * for a given character attribute.
 */
	static int
attr_ewidth(a)
	int a;
{
	int w = 0;

	a = apply_at_specials(a);

	if (a & AT_UNDERLINE)
		w += ul_e_width;
	if (a & AT_BOLD)
		w += bo_e_width;
	if (a & AT_BLINK)
		w += bl_e_width;
	if (a & AT_STANDOUT)
		w += so_e_width;

	return w;
}

/*
 * Return the printing width of a given character and attribute,
 * if the character were added to the current position in the line buffer.
 * Adding a character with a given attribute may cause an enter or exit
 * attribute sequence to be inserted, so this must be taken into account.
 */
	static int
pwidth(ch, a, prev_ch)
	LWCHAR ch;
	int a;
	LWCHAR prev_ch;
{
	int w;

	if (ch == '\b')
		/*
		 * Backspace moves backwards one or two positions.
		 * XXX - Incorrect if several '\b' in a row.
		 */
		return (utf_mode && is_wide_char(prev_ch)) ? -2 : -1;

	if (!utf_mode || is_ascii_char(ch))
	{
		if (control_char((char)ch))
		{
			/*
			 * Control characters do unpredictable things,
			 * so we don't even try to guess; say it doesn't move.
			 * This can only happen if the -r flag is in effect.
			 */
			return (0);
		}
	} else
	{
		if (is_composing_char(ch) || is_combining_char(prev_ch, ch))
		{
			/*
			 * Composing and combining chars take up no space.
			 *
			 * Some terminals, upon failure to compose a
			 * composing character with the character(s) that
			 * precede(s) it will actually take up one column
			 * for the composing character; there isn't much
			 * we could do short of testing the (complex)
			 * composition process ourselves and printing
			 * a binary representation when it fails.
			 */
			return (0);
		}
	}

	/*
	 * Other characters take one or two columns,
	 * plus the width of any attribute enter/exit sequence.
	 */
	w = 1;
	if (is_wide_char(ch))
		w++;
	if (curr > 0 && !is_at_equiv(attr[curr-1], a))
		w += attr_ewidth(attr[curr-1]);
	if ((apply_at_specials(a) != AT_NORMAL) &&
	    (curr == 0 || !is_at_equiv(attr[curr-1], a)))
		w += attr_swidth(a);
	return (w);
}

/*
 * Delete to the previous base character in the line buffer.
 * Return 1 if one is found.
 */
	static int
backc()
{
	LWCHAR prev_ch;
	char *p = linebuf + curr;
	LWCHAR ch = step_char(&p, -1, linebuf + lmargin);
	int width;

	/* This assumes that there is no '\b' in linebuf.  */
	while (   curr > lmargin
	       && column > lmargin
	       && (!(attr[curr - 1] & (AT_ANSI|AT_BINARY))))
	{
		curr = (int) (p - linebuf);
		prev_ch = step_char(&p, -1, linebuf + lmargin);
		width = pwidth(ch, attr[curr], prev_ch);
		column -= width;
		if (width > 0)
			return 1;
		ch = prev_ch;
	}

	return 0;
}

/*
 * Are we currently within a recognized ANSI escape sequence?
 */
	static int
in_ansi_esc_seq()
{
	char *p;

	/*
	 * Search backwards for either an ESC (which means we ARE in a seq);
	 * or an end char (which means we're NOT in a seq).
	 */
	for (p = &linebuf[curr];  p > linebuf; )
	{
		LWCHAR ch = step_char(&p, -1, linebuf);
		if (IS_CSI_START(ch))
			return (1);
		if (!is_ansi_middle(ch))
			return (0);
	}
	return (0);
}

/*
 * Is a character the end of an ANSI escape sequence?
 */
	public int
is_ansi_end(ch)
	LWCHAR ch;
{
	if (!is_ascii_char(ch))
		return (0);
	return (strchr(end_ansi_chars, (char) ch) != NULL);
}

/*
 * Can a char appear in an ANSI escape sequence, before the end char?
 */
	public int
is_ansi_middle(ch)
	LWCHAR ch;
{
	if (!is_ascii_char(ch))
		return (0);
	if (is_ansi_end(ch))
		return (0);
	return (strchr(mid_ansi_chars, (char) ch) != NULL);
}

/*
 * Skip past an ANSI escape sequence.
 * pp is initially positioned just after the CSI_START char.
 */
	public void
skip_ansi(pp, limit)
	char **pp;
	constant char *limit;
{
	LWCHAR c;
	do {
		c = step_char(pp, +1, limit);
	} while (*pp < limit && is_ansi_middle(c));
	/* Note that we discard final char, for which is_ansi_middle is false. */
}


/*
 * Append a character and attribute to the line buffer.
 */
#define	STORE_CHAR(ch,a,rep,pos) \
	do { \
		if (store_char((ch),(a),(rep),(pos))) return (1); \
	} while (0)

	static int
store_char(ch, a, rep, pos)
	LWCHAR ch;
	int a;
	char *rep;
	POSITION pos;
{
	int w;
	int replen;
	char cs;

	w = (a & (AT_UNDERLINE|AT_BOLD));	/* Pre-use w.  */
	if (w != AT_NORMAL)
		last_overstrike = w;

#if HILITE_SEARCH
	{
		int matches;
		if (is_hilited(pos, pos+1, 0, &matches))
		{
			/*
			 * This character should be highlighted.
			 * Override the attribute passed in.
			 */
			if (a != AT_ANSI)
			{
				if (highest_hilite != NULL_POSITION &&
				    pos > highest_hilite)
				    	highest_hilite = pos;
				a |= AT_HILITE;
			}
		}
	}
#endif

	if (ctldisp == OPT_ONPLUS && in_ansi_esc_seq())
	{
		if (!is_ansi_end(ch) && !is_ansi_middle(ch)) {
			/* Remove whole unrecognized sequence.  */
			char *p = &linebuf[curr];
			LWCHAR bch;
			do {
				bch = step_char(&p, -1, linebuf);
			} while (p > linebuf && !IS_CSI_START(bch));
			curr = (int) (p - linebuf);
			return 0;
		}
		a = AT_ANSI;	/* Will force re-AT_'ing around it.  */
		w = 0;
	}
	else if (ctldisp == OPT_ONPLUS && IS_CSI_START(ch))
	{
		a = AT_ANSI;	/* Will force re-AT_'ing around it.  */
		w = 0;
	}
	else
	{
		char *p = &linebuf[curr];
		LWCHAR prev_ch = step_char(&p, -1, linebuf);
		w = pwidth(ch, a, prev_ch);
	}

	if (ctldisp != OPT_ON && column + w + attr_ewidth(a) > sc_width)
		/*
		 * Won't fit on screen.
		 */
		return (1);

	if (rep == NULL)
	{
		cs = (char) ch;
		rep = &cs;
		replen = 1;
	} else
	{
		replen = utf_len(rep[0]);
	}
	if (curr + replen >= size_linebuf-6)
	{
		/*
		 * Won't fit in line buffer.
		 * Try to expand it.
		 */
		if (expand_linebuf())
			return (1);
	}

	if (column > right_column && w > 0)
	{
		right_column = column;
		right_curr = curr;
	}

	while (replen-- > 0)
	{
		add_linebuf(*rep++, a, 0);
	}
	column += w;
	return (0);
}

/*
 * Append a tab to the line buffer.
 * Store spaces to represent the tab.
 */
#define	STORE_TAB(a,pos) \
	do { if (store_tab((a),(pos))) return (1); } while (0)

	static int
store_tab(attr, pos)
	int attr;
	POSITION pos;
{
	int to_tab = column + cshift - lmargin;
	int i;

	if (ntabstops < 2 || to_tab >= tabstops[ntabstops-1])
		to_tab = tabdefault -
		     ((to_tab - tabstops[ntabstops-1]) % tabdefault);
	else
	{
		for (i = ntabstops - 2;  i >= 0;  i--)
			if (to_tab >= tabstops[i])
				break;
		to_tab = tabstops[i+1] - to_tab;
	}

	if (column + to_tab - 1 + pwidth(' ', attr, 0) + attr_ewidth(attr) > sc_width)
		return 1;

	do {
		STORE_CHAR(' ', attr, " ", pos);
	} while (--to_tab > 0);
	return 0;
}

#define STORE_PRCHAR(c, pos) \
	do { if (store_prchar((c), (pos))) return 1; } while (0)

	static int
store_prchar(c, pos)
	LWCHAR c;
	POSITION pos;
{
	char *s;

	/*
	 * Convert to printable representation.
	 */
	s = prchar(c);

	/*
	 * Make sure we can get the entire representation
	 * of the character on this line.
	 */
	if (column + (int) strlen(s) - 1 +
            pwidth(' ', binattr, 0) + attr_ewidth(binattr) > sc_width)
		return 1;

	for ( ;  *s != 0;  s++)
		STORE_CHAR(*s, AT_BINARY, NULL, pos);

	return 0;
}

	static int
flush_mbc_buf(pos)
	POSITION pos;
{
	int i;

	for (i = 0; i < mbc_buf_index; i++)
		if (store_prchar(mbc_buf[i], pos))
			return mbc_buf_index - i;

	return 0;
}

/*
 * Append a character to the line buffer.
 * Expand tabs into spaces, handle underlining, boldfacing, etc.
 * Returns 0 if ok, 1 if couldn't fit in buffer.
 */
	public int
pappend(c, pos)
	unsigned char c;
	POSITION pos;
{
	int r;

	if (pendc)
	{
		if (c == '\r' && pendc == '\r')
			return (0);
		if (do_append(pendc, NULL, pendpos))
			/*
			 * Oops.  We've probably lost the char which
			 * was in pendc, since caller won't back up.
			 */
			return (1);
		pendc = '\0';
	}

	if (c == '\r' && bs_mode == BS_SPECIAL)
	{
		if (mbc_buf_len > 0)  /* utf_mode must be on. */
		{
			/* Flush incomplete (truncated) sequence. */
			r = flush_mbc_buf(mbc_pos);
			mbc_buf_index = r + 1;
			mbc_buf_len = 0;
			if (r)
				return (mbc_buf_index);
		}

		/*
		 * Don't put the CR into the buffer until we see
		 * the next char.  If the next char is a newline,
		 * discard the CR.
		 */
		pendc = c;
		pendpos = pos;
		return (0);
	}

	if (!utf_mode)
	{
		r = do_append(c, NULL, pos);
	} else
	{
		/* Perform strict validation in all possible cases. */
		if (mbc_buf_len == 0)
		{
		retry:
			mbc_buf_index = 1;
			*mbc_buf = c;
			if (IS_ASCII_OCTET(c))
				r = do_append(c, NULL, pos);
			else if (IS_UTF8_LEAD(c))
			{
				mbc_buf_len = utf_len(c);
				mbc_pos = pos;
				return (0);
			} else
				/* UTF8_INVALID or stray UTF8_TRAIL */
				r = flush_mbc_buf(pos);
		} else if (IS_UTF8_TRAIL(c))
		{
			mbc_buf[mbc_buf_index++] = c;
			if (mbc_buf_index < mbc_buf_len)
				return (0);
			if (is_utf8_well_formed(mbc_buf, mbc_buf_index))
				r = do_append(get_wchar(mbc_buf), mbc_buf, mbc_pos);
			else
				/* Complete, but not shortest form, sequence. */
				mbc_buf_index = r = flush_mbc_buf(mbc_pos);
			mbc_buf_len = 0;
		} else
		{
			/* Flush incomplete (truncated) sequence.  */
			r = flush_mbc_buf(mbc_pos);
			mbc_buf_index = r + 1;
			mbc_buf_len = 0;
			/* Handle new char.  */
			if (!r)
				goto retry;
 		}
	}

	/*
	 * If we need to shift the line, do it.
	 * But wait until we get to at least the middle of the screen,
	 * so shifting it doesn't affect the chars we're currently
	 * pappending.  (Bold & underline can get messed up otherwise.)
	 */
	if (cshift < hshift && column > sc_width / 2)
	{
		linebuf[curr] = '\0';
		pshift(hshift - cshift);
	}
	if (r)
	{
		/* How many chars should caller back up? */
		r = (!utf_mode) ? 1 : mbc_buf_index;
	}
	return (r);
}

	static int
do_append(ch, rep, pos)
	LWCHAR ch;
	char *rep;
	POSITION pos;
{
	int a;
	LWCHAR prev_ch;

	a = AT_NORMAL;

	if (ch == '\b')
	{
		if (bs_mode == BS_CONTROL)
			goto do_control_char;

		/*
		 * A better test is needed here so we don't
		 * backspace over part of the printed
		 * representation of a binary character.
		 */
		if (   curr <= lmargin
		    || column <= lmargin
		    || (attr[curr - 1] & (AT_ANSI|AT_BINARY)))
			STORE_PRCHAR('\b', pos);
		else if (bs_mode == BS_NORMAL)
			STORE_CHAR(ch, AT_NORMAL, NULL, pos);
		else if (bs_mode == BS_SPECIAL)
			overstrike = backc();

		return 0;
	}

	if (overstrike > 0)
	{
		/*
		 * Overstrike the character at the current position
		 * in the line buffer.  This will cause either
		 * underline (if a "_" is overstruck),
		 * bold (if an identical character is overstruck),
		 * or just deletion of the character in the buffer.
		 */
		overstrike = utf_mode ? -1 : 0;
		if (utf_mode)
		{
			/* To be correct, this must be a base character.  */
			prev_ch = get_wchar(linebuf + curr);
		} else
		{
			prev_ch = (unsigned char) linebuf[curr];
		}
		a = attr[curr];
		if (ch == prev_ch)
		{
			/*
			 * Overstriking a char with itself means make it bold.
			 * But overstriking an underscore with itself is
			 * ambiguous.  It could mean make it bold, or
			 * it could mean make it underlined.
			 * Use the previous overstrike to resolve it.
			 */
			if (ch == '_')
			{
				if ((a & (AT_BOLD|AT_UNDERLINE)) != AT_NORMAL)
					a |= (AT_BOLD|AT_UNDERLINE);
				else if (last_overstrike != AT_NORMAL)
					a |= last_overstrike;
				else
					a |= AT_BOLD;
			} else
				a |= AT_BOLD;
		} else if (ch == '_')
		{
			a |= AT_UNDERLINE;
			ch = prev_ch;
			rep = linebuf + curr;
		} else if (prev_ch == '_')
		{
			a |= AT_UNDERLINE;
		}
		/* Else we replace prev_ch, but we keep its attributes.  */
	} else if (overstrike < 0)
	{
		if (   is_composing_char(ch)
		    || is_combining_char(get_wchar(linebuf + curr), ch))
			/* Continuation of the same overstrike.  */
			a = last_overstrike;
		else
			overstrike = 0;
	}

	if (ch == '\t')
	{
		/*
		 * Expand a tab into spaces.
		 */
		switch (bs_mode)
		{
		case BS_CONTROL:
			goto do_control_char;
		case BS_NORMAL:
		case BS_SPECIAL:
			STORE_TAB(a, pos);
			break;
		}
	} else if ((!utf_mode || is_ascii_char(ch)) && control_char((char)ch))
	{
	do_control_char:
		if (ctldisp == OPT_ON || (ctldisp == OPT_ONPLUS && IS_CSI_START(ch)))
		{
			/*
			 * Output as a normal character.
			 */
			STORE_CHAR(ch, AT_NORMAL, rep, pos);
		} else
		{
			STORE_PRCHAR((char) ch, pos);
		}
	} else if (utf_mode && ctldisp != OPT_ON && is_ubin_char(ch))
	{
		char *s;

		s = prutfchar(ch);

		if (column + (int) strlen(s) - 1 +
		    pwidth(' ', binattr, 0) + attr_ewidth(binattr) > sc_width)
			return (1);

		for ( ;  *s != 0;  s++)
			STORE_CHAR(*s, AT_BINARY, NULL, pos);
 	} else
	{
		STORE_CHAR(ch, a, rep, pos);
	}
 	return (0);
}

/*
 *
 */
	public int
pflushmbc()
{
	int r = 0;

	if (mbc_buf_len > 0)
	{
		/* Flush incomplete (truncated) sequence.  */
		r = flush_mbc_buf(mbc_pos);
		mbc_buf_len = 0;
	}
	return r;
}

/*
 * Switch to normal attribute at end of line.
 */
	static void
add_attr_normal()
{
	char *p = "\033[m";

	if (ctldisp != OPT_ONPLUS || !is_ansi_end('m'))
		return;
	for ( ;  *p != '\0';  p++)
		add_linebuf(*p, AT_ANSI, 0);
}

/*
 * Terminate the line in the line buffer.
 */
	public void
pdone(endline, chopped, forw)
	int endline;
	int chopped;
	int forw;
{
	(void) pflushmbc();

	if (pendc && (pendc != '\r' || !endline))
		/*
		 * If we had a pending character, put it in the buffer.
		 * But discard a pending CR if we are at end of line
		 * (that is, discard the CR in a CR/LF sequence).
		 */
		(void) do_append(pendc, NULL, pendpos);

	/*
	 * Make sure we've shifted the line, if we need to.
	 */
	if (cshift < hshift)
		pshift(hshift - cshift);

	if (chopped && rscroll_char)
	{
		/*
		 * Display the right scrolling char.
		 * If we've already filled the rightmost screen char
		 * (in the buffer), overwrite it.
		 */
		if (column >= sc_width)
		{
			/* We've already written in the rightmost char. */
			column = right_column;
			curr = right_curr;
		}
		add_attr_normal();
		while (column < sc_width-1)
		{
			/*
			 * Space to last (rightmost) char on screen.
			 * This may be necessary if the char we overwrote
			 * was double-width.
			 */
			add_linebuf(' ', AT_NORMAL, 1);
		}
		/* Print rscroll char. It must be single-width. */
		add_linebuf(rscroll_char, rscroll_attr, 1);
	} else
	{
		add_attr_normal();
	}

	/*
	 * Add a newline if necessary,
	 * and append a '\0' to the end of the line.
	 * We output a newline if we're not at the right edge of the screen,
	 * or if the terminal doesn't auto wrap,
	 * or if this is really the end of the line AND the terminal ignores
	 * a newline at the right edge.
	 * (In the last case we don't want to output a newline if the terminal
	 * doesn't ignore it since that would produce an extra blank line.
	 * But we do want to output a newline if the terminal ignores it in case
	 * the next line is blank.  In that case the single newline output for
	 * that blank line would be ignored!)
	 */
	if (column < sc_width || !auto_wrap || (endline && ignaw) || ctldisp == OPT_ON)
	{
		add_linebuf('\n', AT_NORMAL, 0);
	}
	else if (ignaw && column >= sc_width && forw)
	{
		/*
		 * Terminals with "ignaw" don't wrap until they *really* need
		 * to, i.e. when the character *after* the last one to fit on a
		 * line is output. But they are too hard to deal with when they
		 * get in the state where a full screen width of characters
		 * have been output but the cursor is sitting on the right edge
		 * instead of at the start of the next line.
		 * So we nudge them into wrapping by outputting a space
		 * character plus a backspace.  But do this only if moving
		 * forward; if we're moving backward and drawing this line at
		 * the top of the screen, the space would overwrite the first
		 * char on the next line.  We don't need to do this "nudge"
		 * at the top of the screen anyway.
		 */
		add_linebuf(' ', AT_NORMAL, 1);
		add_linebuf('\b', AT_NORMAL, -1);
	}
	set_linebuf(curr, '\0', AT_NORMAL);
}

/*
 *
 */
	public void
set_status_col(c)
	char c;
{
	set_linebuf(0, c, AT_NORMAL|AT_HILITE);
}

/*
 * Get a character from the current line.
 * Return the character as the function return value,
 * and the character attribute in *ap.
 */
	public int
gline(i, ap)
	int i;
	int *ap;
{
	if (is_null_line)
	{
		/*
		 * If there is no current line, we pretend the line is
		 * either "~" or "", depending on the "twiddle" flag.
		 */
		if (twiddle)
		{
			if (i == 0)
			{
				*ap = AT_BOLD;
				return '~';
			}
			--i;
		}
		/* Make sure we're back to AT_NORMAL before the '\n'.  */
		*ap = AT_NORMAL;
		return i ? '\0' : '\n';
	}

	*ap = attr[i];
	return (linebuf[i] & 0xFF);
}

/*
 * Indicate that there is no current line.
 */
	public void
null_line()
{
	is_null_line = 1;
	cshift = 0;
}

/*
 * Analogous to forw_line(), but deals with "raw lines":
 * lines which are not split for screen width.
 * {{ This is supposed to be more efficient than forw_line(). }}
 */
	public POSITION
forw_raw_line(curr_pos, linep, line_lenp)
	POSITION curr_pos;
	char **linep;
	int *line_lenp;
{
	int n;
	int c;
	POSITION new_pos;

	if (curr_pos == NULL_POSITION || ch_seek(curr_pos) ||
		(c = ch_forw_get()) == EOI)
		return (NULL_POSITION);

	n = 0;
	for (;;)
	{
		if (c == '\n' || c == EOI || ABORT_SIGS())
		{
			new_pos = ch_tell();
			break;
		}
		if (n >= size_linebuf-1)
		{
			if (expand_linebuf())
			{
				/*
				 * Overflowed the input buffer.
				 * Pretend the line ended here.
				 */
				new_pos = ch_tell() - 1;
				break;
			}
		}
		linebuf[n++] = c;
		c = ch_forw_get();
	}
	linebuf[n] = '\0';
	if (linep != NULL)
		*linep = linebuf;
	if (line_lenp != NULL)
		*line_lenp = n;
	return (new_pos);
}

/*
 * Analogous to back_line(), but deals with "raw lines".
 * {{ This is supposed to be more efficient than back_line(). }}
 */
	public POSITION
back_raw_line(curr_pos, linep, line_lenp)
	POSITION curr_pos;
	char **linep;
	int *line_lenp;
{
	int n;
	int c;
	POSITION new_pos;

	if (curr_pos == NULL_POSITION || curr_pos <= ch_zero() ||
		ch_seek(curr_pos-1))
		return (NULL_POSITION);

	n = size_linebuf;
	linebuf[--n] = '\0';
	for (;;)
	{
		c = ch_back_get();
		if (c == '\n' || ABORT_SIGS())
		{
			/*
			 * This is the newline ending the previous line.
			 * We have hit the beginning of the line.
			 */
			new_pos = ch_tell() + 1;
			break;
		}
		if (c == EOI)
		{
			/*
			 * We have hit the beginning of the file.
			 * This must be the first line in the file.
			 * This must, of course, be the beginning of the line.
			 */
			new_pos = ch_zero();
			break;
		}
		if (n <= 0)
		{
			int old_size_linebuf = size_linebuf;
			char *fm;
			char *to;
			if (expand_linebuf())
			{
				/*
				 * Overflowed the input buffer.
				 * Pretend the line ended here.
				 */
				new_pos = ch_tell() + 1;
				break;
			}
			/*
			 * Shift the data to the end of the new linebuf.
			 */
			for (fm = linebuf + old_size_linebuf - 1,
			      to = linebuf + size_linebuf - 1;
			     fm >= linebuf;  fm--, to--)
				*to = *fm;
			n = size_linebuf - old_size_linebuf;
		}
		linebuf[--n] = c;
	}
	if (linep != NULL)
		*linep = &linebuf[n];
	if (line_lenp != NULL)
		*line_lenp = size_linebuf - 1 - n;
	return (new_pos);
}

/*
 * Find the shift necessary to show the end of the longest displayed line.
 */
	public int
rrshift()
{
	POSITION pos;
	int save_width;
	int line;
	int longest = 0;

	save_width = sc_width;
	sc_width = INT_MAX;
	hshift = 0;
	pos = position(TOP);
	for (line = 0; line < sc_height && pos != NULL_POSITION; line++)
	{
		pos = forw_line(pos);
		if (column > longest)
			longest = column;
	}
	sc_width = save_width;
	if (longest < sc_width)
		return 0;
	return longest - sc_width;
}