[platform/upstream/bash.git] / lib / readline / display.c

/* display.c -- readline redisplay facility. */

/* Copyright (C) 1987, 1989, 1992 Free Software Foundation, Inc.

   This file is part of the GNU Readline Library, a library for
   reading lines of text with interactive input and history editing.

   The GNU Readline Library is free software; you can redistribute it
   and/or modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 1, or
   (at your option) any later version.

   The GNU Readline Library is distributed in the hope that it will be
   useful, but WITHOUT ANY WARRANTY; without even the implied warranty
   of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   The GNU General Public License is often shipped with GNU software, and
   is generally kept in a file called COPYING or LICENSE.  If you do not
   have a copy of the license, write to the Free Software Foundation,
   675 Mass Ave, Cambridge, MA 02139, USA. */
#define READLINE_LIBRARY

#if defined (HAVE_CONFIG_H)
#  include <config.h>
#endif

#include <sys/types.h>

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif /* HAVE_UNISTD_H */

#include "posixstat.h"

#if defined (HAVE_STDLIB_H)
#  include <stdlib.h>
#else
#  include "ansi_stdlib.h"
#endif /* HAVE_STDLIB_H */

#include <stdio.h>

#if defined (__GO32__)
#  include <go32.h>
#  include <pc.h>
#endif /* __GO32__ */

/* System-specific feature definitions and include files. */
#include "rldefs.h"

/* Termcap library stuff. */
#include "tcap.h"

/* Some standard library routines. */
#include "readline.h"
#include "history.h"

#if !defined (strchr) && !defined (__STDC__)
extern char *strchr (), *strrchr ();
#endif /* !strchr && !__STDC__ */

/* Global and pseudo-global variables and functions
   imported from readline.c. */
extern char *rl_prompt;
extern int readline_echoing_p;

extern int _rl_output_meta_chars;
extern int _rl_horizontal_scroll_mode;
extern int _rl_mark_modified_lines;
extern int _rl_prefer_visible_bell;

/* Variables and functions imported from terminal.c */
extern void _rl_output_some_chars ();
#ifdef _MINIX
extern void _rl_output_character_function ();
#else
extern int _rl_output_character_function ();
#endif
extern int _rl_backspace ();

extern char *term_clreol, *term_clrpag;
extern char *term_im, *term_ic,  *term_ei, *term_DC;
extern char *term_up, *term_dc, *term_cr, *term_IC;
extern int screenheight, screenwidth, screenchars;
extern int terminal_can_insert, _rl_term_autowrap;

/* Pseudo-global functions (local to the readline library) exported
   by this file. */
void _rl_move_cursor_relative (), _rl_output_some_chars ();
void _rl_move_vert ();
void _rl_clear_to_eol (), _rl_clear_screen ();

static void update_line (), space_to_eol ();
static void delete_chars (), insert_some_chars ();
static void cr ();

static int *inv_lbreaks, *vis_lbreaks;

extern char *xmalloc (), *xrealloc ();

/* Heuristic used to decide whether it is faster to move from CUR to NEW
   by backing up or outputting a carriage return and moving forward. */
#define CR_FASTER(new, cur) (((new) + 1) < ((cur) - (new)))

/* **************************************************************** */
/*                                                                  */
/*                      Display stuff                               */
/*                                                                  */
/* **************************************************************** */

/* This is the stuff that is hard for me.  I never seem to write good
   display routines in C.  Let's see how I do this time. */

/* (PWP) Well... Good for a simple line updater, but totally ignores
   the problems of input lines longer than the screen width.

   update_line and the code that calls it makes a multiple line,
   automatically wrapping line update.  Careful attention needs
   to be paid to the vertical position variables. */

/* Keep two buffers; one which reflects the current contents of the
   screen, and the other to draw what we think the new contents should
   be.  Then compare the buffers, and make whatever changes to the
   screen itself that we should.  Finally, make the buffer that we
   just drew into be the one which reflects the current contents of the
   screen, and place the cursor where it belongs.

   Commands that want to can fix the display themselves, and then let
   this function know that the display has been fixed by setting the
   RL_DISPLAY_FIXED variable.  This is good for efficiency. */

/* Application-specific redisplay function. */
VFunction *rl_redisplay_function = rl_redisplay;

/* Global variables declared here. */
/* What YOU turn on when you have handled all redisplay yourself. */
int rl_display_fixed = 0;

int _rl_suppress_redisplay = 0;

/* The stuff that gets printed out before the actual text of the line.
   This is usually pointing to rl_prompt. */
char *rl_display_prompt = (char *)NULL;

/* Pseudo-global variables declared here. */
/* The visible cursor position.  If you print some text, adjust this. */
int _rl_last_c_pos = 0;
int _rl_last_v_pos = 0;

/* Number of lines currently on screen minus 1. */
int _rl_vis_botlin = 0;

/* Variables used only in this file. */
/* The last left edge of text that was displayed.  This is used when
   doing horizontal scrolling.  It shifts in thirds of a screenwidth. */
static int last_lmargin;

/* The line display buffers.  One is the line currently displayed on
   the screen.  The other is the line about to be displayed. */
static char *visible_line = (char *)NULL;
static char *invisible_line = (char *)NULL;

/* A buffer for `modeline' messages. */
static char msg_buf[128];

/* Non-zero forces the redisplay even if we thought it was unnecessary. */
static int forced_display;

/* Default and initial buffer size.  Can grow. */
static int line_size = 1024;

static char *local_prompt, *local_prompt_prefix;
static int visible_length, prefix_length;

/* The number of invisible characters in the line currently being
   displayed on the screen. */
static int visible_wrap_offset;

/* static so it can be shared between rl_redisplay and update_line */
static int wrap_offset;

/* The index of the last invisible_character in the prompt string. */
static int last_invisible;

/* The length (buffer offset) of the first line of the last (possibly
   multi-line) buffer displayed on the screen. */
static int visible_first_line_len;

/* Expand the prompt string S and return the number of visible
   characters in *LP, if LP is not null.  This is currently more-or-less
   a placeholder for expansion.  LIP, if non-null is a place to store the
   index of the last invisible character in ther eturned string. */

/* Current implementation:
        \001 (^A) start non-visible characters
        \002 (^B) end non-visible characters
   all characters except \001 and \002 (following a \001) are copied to
   the returned string; all characters except those between \001 and
   \002 are assumed to be `visible'. */ 

static char *
expand_prompt (pmt, lp, lip)
     char *pmt;
     int *lp, *lip;
{
  char *r, *ret, *p;
  int l, rl, last, ignoring;

  /* Short-circuit if we can. */
  if (strchr (pmt, RL_PROMPT_START_IGNORE) == 0)
    {
      r = savestring (pmt);
      if (lp)
        *lp = strlen (r);
      return r;
    }

  l = strlen (pmt);
  r = ret = xmalloc (l + 1);
  
  for (rl = ignoring = last = 0, p = pmt; p && *p; p++)
    {
      /* This code strips the invisible character string markers
         RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE */
      if (*p == RL_PROMPT_START_IGNORE)
        {
          ignoring++;
          continue;
        }
      else if (ignoring && *p == RL_PROMPT_END_IGNORE)
        {
          ignoring = 0;
          last = r - ret - 1;
          continue;
        }
      else
        {
          *r++ = *p;
          if (!ignoring)
            rl++;
        }
    }

  *r = '\0';
  if (lp)
    *lp = rl;
  if (lip)
    *lip = last;
  return ret;
}

/*
 * Expand the prompt string into the various display components, if
 * necessary.
 *
 * local_prompt = expanded last line of string in rl_display_prompt
 *                (portion after the final newline)
 * local_prompt_prefix = portion before last newline of rl_display_prompt,
 *                       expanded via expand_prompt
 * visible_length = number of visible characters in local_prompt
 * prefix_length = number of visible characters in local_prompt_prefix
 *
 * This function is called once per call to readline().  It may also be
 * called arbitrarily to expand the primary prompt.
 *
 * The return value is the number of visible characters on the last line
 * of the (possibly multi-line) prompt.
 */
int
rl_expand_prompt (prompt)
     char *prompt;
{
  char *p, *t;
  int c;

  /* Clear out any saved values. */
  if (local_prompt)
    free (local_prompt);
  if (local_prompt_prefix)
    free (local_prompt_prefix);
  local_prompt = local_prompt_prefix = (char *)0;
  last_invisible = 0;

  if (prompt == 0 || *prompt == 0)
    return (0);

  p = strrchr (prompt, '\n');
  if (!p)
    {
      /* The prompt is only one line. */
      local_prompt = expand_prompt (prompt, &visible_length, &last_invisible);
      local_prompt_prefix = (char *)0;
      return (visible_length);
    }
  else
    {
      /* The prompt spans multiple lines. */
      t = ++p;
      local_prompt = expand_prompt (p, &visible_length, &last_invisible);
      c = *t; *t = '\0';
      /* The portion of the prompt string up to and including the
         final newline is now null-terminated. */
      local_prompt_prefix = expand_prompt (prompt, &prefix_length, (int *)NULL);
      *t = c;
      return (prefix_length);
    }
}

/* Basic redisplay algorithm. */
void
rl_redisplay ()
{
  register int in, out, c, linenum, cursor_linenum;
  register char *line;
  int c_pos, inv_botlin, lb_botlin, lb_linenum;
  int newlines, lpos, temp;
  char *prompt_this_line;

  if (!readline_echoing_p)
    return;

  if (!rl_display_prompt)
    rl_display_prompt = "";

  if (invisible_line == 0)
    {
      visible_line = xmalloc (line_size);
      invisible_line = xmalloc (line_size);
      for (in = 0; in < line_size; in++)
        {
          visible_line[in] = 0;
          invisible_line[in] = 1;
        }

      /* should be enough, but then again, this is just for testing. */
      inv_lbreaks = (int *)malloc (256 * sizeof (int));
      vis_lbreaks = (int *)malloc (256 * sizeof (int));
      inv_lbreaks[0] = vis_lbreaks[0] = 0;

      rl_on_new_line ();
    }

  /* Draw the line into the buffer. */
  c_pos = -1;

  line = invisible_line;
  out = inv_botlin = 0;

  /* Mark the line as modified or not.  We only do this for history
     lines. */
  if (_rl_mark_modified_lines && current_history () && rl_undo_list)
    {
      line[out++] = '*';
      line[out] = '\0';
    }

  /* If someone thought that the redisplay was handled, but the currently
     visible line has a different modification state than the one about
     to become visible, then correct the caller's misconception. */
  if (visible_line[0] != invisible_line[0])
    rl_display_fixed = 0;

  /* If the prompt to be displayed is the `primary' readline prompt (the
     one passed to readline()), use the values we have already expanded.
     If not, use what's already in rl_display_prompt.  WRAP_OFFSET is the
     number of non-visible characters in the prompt string. */
  if (rl_display_prompt == rl_prompt || local_prompt)
    {
      int local_len = local_prompt ? strlen (local_prompt) : 0;
      if (local_prompt_prefix && forced_display)
        _rl_output_some_chars (local_prompt_prefix, strlen (local_prompt_prefix));

      if (local_len > 0)
        {
          strncpy (line + out, local_prompt, local_len);
          out += local_len;
        }
      line[out] = '\0';
      wrap_offset = local_len - visible_length;
    }
  else
    {
      int pmtlen;
      prompt_this_line = strrchr (rl_display_prompt, '\n');
      if (!prompt_this_line)
        prompt_this_line = rl_display_prompt;
      else
        {
          prompt_this_line++;
          if (forced_display)
            {
              _rl_output_some_chars (rl_display_prompt, prompt_this_line - rl_display_prompt);
              /* Make sure we are at column zero even after a newline,
                 regardless of the state of terminal output processing. */
              if (prompt_this_line[-2] != '\r')
                cr ();
            }
        }

      pmtlen = strlen (prompt_this_line);
      strncpy (line + out,  prompt_this_line, pmtlen);
      out += pmtlen;
      line[out] = '\0';
      wrap_offset = 0;
    }

#define CHECK_LPOS() \
      do { \
        lpos++; \
        if (lpos >= screenwidth) \
          { \
            inv_lbreaks[++newlines] = out; \
            lpos = 0; \
          } \
      } while (0)

  /* inv_lbreaks[i] is where line i starts in the buffer. */
  inv_lbreaks[newlines = 0] = 0;
  lpos = out - wrap_offset;

  /* XXX - what if lpos is already >= screenwidth before we start drawing the
     contents of the command line? */
  while (lpos >= screenwidth)
    {
#if 0
      temp = ((newlines + 1) * screenwidth) - ((newlines == 0) ? wrap_offset : 0);
#else
      /* XXX - possible fix from Darin Johnson <darin@acuson.com> for prompt
         string with invisible characters that is longer than the screen
         width. */
      temp = ((newlines + 1) * screenwidth) + ((newlines == 0) ? wrap_offset : 0);
#endif
      inv_lbreaks[++newlines] = temp;
      lpos -= screenwidth;
    }

  lb_linenum = 0;
  for (in = 0; in < rl_end; in++)
    {
      c = (unsigned char)rl_line_buffer[in];

      if (out + 8 >= line_size)         /* XXX - 8 for \t */
        {
          line_size *= 2;
          visible_line = xrealloc (visible_line, line_size);
          invisible_line = xrealloc (invisible_line, line_size);
          line = invisible_line;
        }

      if (in == rl_point)
        {
          c_pos = out;
          lb_linenum = newlines;
        }

      if (META_CHAR (c))
        {
          if (_rl_output_meta_chars == 0)
            {
              sprintf (line + out, "\\%o", c);

              if (lpos + 4 >= screenwidth)
                {
                  temp = screenwidth - lpos;
                  inv_lbreaks[++newlines] = out + temp;
                  lpos = 4 - temp;
                }
              else
                lpos += 4;

              out += 4;
            }
          else
            {
              line[out++] = c;
              CHECK_LPOS();
            }
        }
#if defined (DISPLAY_TABS)
      else if (c == '\t')
        {
          register int temp, newout;
          newout = (out | (int)7) + 1;
          temp = newout - out;
          if (lpos + temp >= screenwidth)
            {
              register int temp2;
              temp2 = screenwidth - lpos;
              inv_lbreaks[++newlines] = out + temp2;
              lpos = temp - temp2;
              while (out < newout)
                line[out++] = ' ';
            }
          else
            {
              while (out < newout)
                line[out++] = ' ';
              lpos += temp;
            }
        }
#endif
      else if (c == '\n' && _rl_horizontal_scroll_mode == 0 && term_up && *term_up)
        {
          line[out++] = '\0';   /* XXX - sentinel */
          inv_lbreaks[++newlines] = out;
          lpos = 0;
        }
      else if (CTRL_CHAR (c) || c == RUBOUT)
        {
          line[out++] = '^';
          CHECK_LPOS();
          line[out++] = CTRL_CHAR (c) ? UNCTRL (c) : '?';
          CHECK_LPOS();
        }
      else
        {
          line[out++] = c;
          CHECK_LPOS();
        }
    }
  line[out] = '\0';
  if (c_pos < 0)
    {
      c_pos = out;
      lb_linenum = newlines;
    }

  inv_botlin = lb_botlin = newlines;
  inv_lbreaks[newlines+1] = out;
  cursor_linenum = lb_linenum;

  /* C_POS == position in buffer where cursor should be placed. */

  /* PWP: now is when things get a bit hairy.  The visible and invisible
     line buffers are really multiple lines, which would wrap every
     (screenwidth - 1) characters.  Go through each in turn, finding
     the changed region and updating it.  The line order is top to bottom. */

  /* If we can move the cursor up and down, then use multiple lines,
     otherwise, let long lines display in a single terminal line, and
     horizontally scroll it. */

  if (_rl_horizontal_scroll_mode == 0 && term_up && *term_up)
    {
      int nleft, pos, changed_screen_line;

      if (!rl_display_fixed || forced_display)
        {
          forced_display = 0;

          /* If we have more than a screenful of material to display, then
             only display a screenful.  We should display the last screen,
             not the first.  */
          if (out >= screenchars)
            out = screenchars - 1;

          /* The first line is at character position 0 in the buffer.  The
             second and subsequent lines start at inv_lbreaks[N], offset by
             OFFSET (which has already been calculated above).  */

#define W_OFFSET(line, offset) ((line) == 0 ? offset : 0)
#define VIS_LLEN(l)     ((l) > _rl_vis_botlin ? 0 : (vis_lbreaks[l+1] - vis_lbreaks[l]))
#define INV_LLEN(l)     (inv_lbreaks[l+1] - inv_lbreaks[l])
#define VIS_CHARS(line) (visible_line + vis_lbreaks[line])
#define VIS_LINE(line) ((line) > _rl_vis_botlin) ? "" : VIS_CHARS(line)
#define INV_LINE(line) (invisible_line + inv_lbreaks[line])

          /* For each line in the buffer, do the updating display. */
          for (linenum = 0; linenum <= inv_botlin; linenum++)
            {
              update_line (VIS_LINE(linenum), INV_LINE(linenum), linenum,
                           VIS_LLEN(linenum), INV_LLEN(linenum), inv_botlin);

              /* If this is the line with the prompt, we might need to
                 compensate for invisible characters in the new line. Do
                 this only if there is not more than one new line (which
                 implies that we completely overwrite the old visible line)
                 and the new line is shorter than the old.  Make sure we are
                 at the end of the new line before clearing. */
              if (linenum == 0 &&
                  inv_botlin == 0 && _rl_last_c_pos == out &&
                  (wrap_offset > visible_wrap_offset) &&
                  (_rl_last_c_pos < visible_first_line_len))
                {
                  nleft = screenwidth + wrap_offset - _rl_last_c_pos;
                  if (nleft)
                    _rl_clear_to_eol (nleft);
                }

              /* Since the new first line is now visible, save its length. */
              if (linenum == 0)
                visible_first_line_len = (inv_botlin > 0) ? inv_lbreaks[1] : out - wrap_offset;
            }

          /* We may have deleted some lines.  If so, clear the left over
             blank ones at the bottom out. */
          if (_rl_vis_botlin > inv_botlin)
            {
              char *tt;
              for (; linenum <= _rl_vis_botlin; linenum++)
                {
                  tt = VIS_CHARS (linenum);
                  _rl_move_vert (linenum);
                  _rl_move_cursor_relative (0, tt);
                  _rl_clear_to_eol
                    ((linenum == _rl_vis_botlin) ? strlen (tt) : screenwidth);
                }
            }
          _rl_vis_botlin = inv_botlin;

          /* CHANGED_SCREEN_LINE is set to 1 if we have moved to a
             different screen line during this redisplay. */
          changed_screen_line = _rl_last_v_pos != cursor_linenum;
          if (changed_screen_line)
            {
              _rl_move_vert (cursor_linenum);
              /* If we moved up to the line with the prompt using term_up,
                 the physical cursor position on the screen stays the same,
                 but the buffer position needs to be adjusted to account
                 for invisible characters. */
              if (cursor_linenum == 0 && wrap_offset)
                _rl_last_c_pos += wrap_offset;
            }

          /* We have to reprint the prompt if it contains invisible
             characters, since it's not generally OK to just reprint
             the characters from the current cursor position.  But we
             only need to reprint it if the cursor is before the last
             invisible character in the prompt string. */
          nleft = visible_length + wrap_offset;
          if (cursor_linenum == 0 && wrap_offset > 0 && _rl_last_c_pos > 0 &&
              _rl_last_c_pos <= last_invisible && local_prompt)
            {
              if (term_cr)
                tputs (term_cr, 1, _rl_output_character_function);
              _rl_output_some_chars (local_prompt, nleft);
              _rl_last_c_pos = nleft;
            }

          /* Where on that line?  And where does that line start
             in the buffer? */
          pos = inv_lbreaks[cursor_linenum];
          /* nleft == number of characters in the line buffer between the
             start of the line and the cursor position. */
          nleft = c_pos - pos;

          /* Since _rl_backspace() doesn't know about invisible characters in the
             prompt, and there's no good way to tell it, we compensate for
             those characters here and call _rl_backspace() directly. */
          if (wrap_offset && cursor_linenum == 0 && nleft < _rl_last_c_pos)
            {
              _rl_backspace (_rl_last_c_pos - nleft);
              _rl_last_c_pos = nleft;
            }

          if (nleft != _rl_last_c_pos)
            _rl_move_cursor_relative (nleft, &invisible_line[pos]);
        }
    }
  else                          /* Do horizontal scrolling. */
    {
#define M_OFFSET(margin, offset) ((margin) == 0 ? offset : 0)
      int lmargin, ndisp, nleft, phys_c_pos, t;

      /* Always at top line. */
      _rl_last_v_pos = 0;

      /* Compute where in the buffer the displayed line should start.  This
         will be LMARGIN. */

      /* The number of characters that will be displayed before the cursor. */
      ndisp = c_pos - wrap_offset;
      nleft  = visible_length + wrap_offset;
      /* Where the new cursor position will be on the screen.  This can be
         longer than SCREENWIDTH; if it is, lmargin will be adjusted. */
      phys_c_pos = c_pos - (last_lmargin ? last_lmargin : wrap_offset);
      t = screenwidth / 3;

      /* If the number of characters had already exceeded the screenwidth,
         last_lmargin will be > 0. */

      /* If the number of characters to be displayed is more than the screen
         width, compute the starting offset so that the cursor is about
         two-thirds of the way across the screen. */
      if (phys_c_pos > screenwidth - 2)
        {
          lmargin = c_pos - (2 * t);
          if (lmargin < 0)
            lmargin = 0;
          /* If the left margin would be in the middle of a prompt with
             invisible characters, don't display the prompt at all. */
          if (wrap_offset && lmargin > 0 && lmargin < nleft)
            lmargin = nleft;
        }
      else if (ndisp < screenwidth - 2)         /* XXX - was -1 */
        lmargin = 0;
      else if (phys_c_pos < 1)
        {
          /* If we are moving back towards the beginning of the line and
             the last margin is no longer correct, compute a new one. */
          lmargin = ((c_pos - 1) / t) * t;      /* XXX */
          if (wrap_offset && lmargin > 0 && lmargin < nleft)
            lmargin = nleft;
        }
      else
        lmargin = last_lmargin;

      /* If the first character on the screen isn't the first character
         in the display line, indicate this with a special character. */
      if (lmargin > 0)
        line[lmargin] = '<';

      /* If SCREENWIDTH characters starting at LMARGIN do not encompass
         the whole line, indicate that with a special characters at the
         right edge of the screen.  If LMARGIN is 0, we need to take the
         wrap offset into account. */
      t = lmargin + M_OFFSET (lmargin, wrap_offset) + screenwidth;
      if (t < out)
        line[t - 1] = '>';

      if (!rl_display_fixed || forced_display || lmargin != last_lmargin)
        {
          forced_display = 0;
          update_line (&visible_line[last_lmargin],
                       &invisible_line[lmargin],
                       0,
                       screenwidth + visible_wrap_offset,
                       screenwidth + (lmargin ? 0 : wrap_offset),
                       0);

          /* If the visible new line is shorter than the old, but the number
             of invisible characters is greater, and we are at the end of
             the new line, we need to clear to eol. */
          t = _rl_last_c_pos - M_OFFSET (lmargin, wrap_offset);
          if ((M_OFFSET (lmargin, wrap_offset) > visible_wrap_offset) &&
              (_rl_last_c_pos == out) &&
              t < visible_first_line_len)
            {
              nleft = screenwidth - t;
              _rl_clear_to_eol (nleft);
            }
          visible_first_line_len = out - lmargin - M_OFFSET (lmargin, wrap_offset);
          if (visible_first_line_len > screenwidth)
            visible_first_line_len = screenwidth;

          _rl_move_cursor_relative (c_pos - lmargin, &invisible_line[lmargin]);
          last_lmargin = lmargin;
        }
    }
  fflush (rl_outstream);

  /* Swap visible and non-visible lines. */
  {
    char *temp = visible_line;
    int *itemp = vis_lbreaks;
    visible_line = invisible_line;
    invisible_line = temp;
    vis_lbreaks = inv_lbreaks;
    inv_lbreaks = itemp;
    rl_display_fixed = 0;
    /* If we are displaying on a single line, and last_lmargin is > 0, we
       are not displaying any invisible characters, so set visible_wrap_offset
       to 0. */
    if (_rl_horizontal_scroll_mode && last_lmargin)
      visible_wrap_offset = 0;
    else
      visible_wrap_offset = wrap_offset;
  }
}

/* PWP: update_line() is based on finding the middle difference of each
   line on the screen; vis:

                             /old first difference
        /beginning of line   |        /old last same       /old EOL
        v                    v        v             v
old:    eddie> Oh, my little gruntle-buggy is to me, as lurgid as
new:    eddie> Oh, my little buggy says to me, as lurgid as
        ^                    ^  ^                          ^
        \beginning of line   |  \new last same     \new end of line
                             \new first difference

   All are character pointers for the sake of speed.  Special cases for
   no differences, as well as for end of line additions must be handeled.

   Could be made even smarter, but this works well enough */
static void
update_line (old, new, current_line, omax, nmax, inv_botlin)
     register char *old, *new;
     int current_line, omax, nmax, inv_botlin;
{
  register char *ofd, *ols, *oe, *nfd, *nls, *ne;
  int temp, lendiff, wsatend, od, nd;
  int current_invis_chars;

  /* If we're at the right edge of a terminal that supports xn, we're
     ready to wrap around, so do so.  This fixes problems with knowing
     the exact cursor position and cut-and-paste with certain terminal
     emulators.  In this calculation, TEMP is the physical screen
     position of the cursor. */
  temp = _rl_last_c_pos - W_OFFSET(_rl_last_v_pos, visible_wrap_offset);
  if (temp == screenwidth && _rl_term_autowrap && !_rl_horizontal_scroll_mode
      && _rl_last_v_pos == current_line - 1)
    {
      if (new[0])
        putc (new[0], rl_outstream);
      else
        putc (' ', rl_outstream);
      _rl_last_c_pos = 1;               /* XXX */
      _rl_last_v_pos++;
      if (old[0] && new[0])
        old[0] = new[0];
    }
      
  /* Find first difference. */
  for (ofd = old, nfd = new;
       (ofd - old < omax) && *ofd && (*ofd == *nfd);
       ofd++, nfd++)
    ;

  /* Move to the end of the screen line.  ND and OD are used to keep track
     of the distance between ne and new and oe and old, respectively, to
     move a subtraction out of each loop. */
  for (od = ofd - old, oe = ofd; od < omax && *oe; oe++, od++);
  for (nd = nfd - new, ne = nfd; nd < nmax && *ne; ne++, nd++);

  /* If no difference, continue to next line. */
  if (ofd == oe && nfd == ne)
    return;

  wsatend = 1;                  /* flag for trailing whitespace */
  ols = oe - 1;                 /* find last same */
  nls = ne - 1;
  while ((ols > ofd) && (nls > nfd) && (*ols == *nls))
    {
      if (*ols != ' ')
        wsatend = 0;
      ols--;
      nls--;
    }

  if (wsatend)
    {
      ols = oe;
      nls = ne;
    }
  else if (*ols != *nls)
    {
      if (*ols)                 /* don't step past the NUL */
        ols++;
      if (*nls)
        nls++;
    }

  /* count of invisible characters in the current invisible line. */
  current_invis_chars = W_OFFSET (current_line, wrap_offset);
  if (_rl_last_v_pos != current_line)
    {
      _rl_move_vert (current_line);
      if (current_line == 0 && visible_wrap_offset)
        _rl_last_c_pos += visible_wrap_offset;
    }

  /* If this is the first line and there are invisible characters in the
     prompt string, and the prompt string has not changed, and the current
     cursor position is before the last invisible character in the prompt,
     and the index of the character to move to is past the end of the prompt
     string, then redraw the entire prompt string.  We can only do this
     reliably if the terminal supports a `cr' capability.

     This is not an efficiency hack -- there is a problem with redrawing
     portions of the prompt string if they contain terminal escape
     sequences (like drawing the `unbold' sequence without a corresponding
     `bold') that manifests itself on certain terminals. */

  lendiff = local_prompt ? strlen (local_prompt) : 0;
  od = ofd - old;       /* index of first difference in visible line */
  if (current_line == 0 && !_rl_horizontal_scroll_mode &&
      term_cr && lendiff > visible_length && _rl_last_c_pos > 0 &&
      od > lendiff && _rl_last_c_pos < last_invisible)
    {
      tputs (term_cr, 1, _rl_output_character_function);
      _rl_output_some_chars (local_prompt, lendiff);
      _rl_last_c_pos = lendiff;
    }

  _rl_move_cursor_relative (od, old);

  /* if (len (new) > len (old)) */
  lendiff = (nls - nfd) - (ols - ofd);

  /* If we are changing the number of invisible characters in a line, and
     the spot of first difference is before the end of the invisible chars,
     lendiff needs to be adjusted. */
  if (current_line == 0 && !_rl_horizontal_scroll_mode &&
      current_invis_chars != visible_wrap_offset)
    {
      temp = visible_wrap_offset - current_invis_chars;
      lendiff += temp;
    }

  /* Insert (diff (len (old), len (new)) ch. */
  temp = ne - nfd;
  if (lendiff > 0)
    {
      /* Non-zero if we're increasing the number of lines. */
      int gl = current_line >= _rl_vis_botlin && inv_botlin > _rl_vis_botlin;
      /* Sometimes it is cheaper to print the characters rather than
         use the terminal's capabilities.  If we're growing the number
         of lines, make sure we actually cause the new line to wrap
         around on auto-wrapping terminals. */
      if (terminal_can_insert && ((2 * temp) >= lendiff || term_IC) && (!_rl_term_autowrap || !gl))
        {
          /* If lendiff > visible_length and _rl_last_c_pos == 0 and
             _rl_horizontal_scroll_mode == 1, inserting the characters with
             term_IC or term_ic will screw up the screen because of the
             invisible characters.  We need to just draw them. */
          if (*ols && (!_rl_horizontal_scroll_mode || _rl_last_c_pos > 0 ||
                        lendiff <= visible_length || !current_invis_chars))
            {
              insert_some_chars (nfd, lendiff);
              _rl_last_c_pos += lendiff;
            }
          else if (*ols == 0)
            {
              /* At the end of a line the characters do not have to
                 be "inserted".  They can just be placed on the screen. */
              /* However, this screws up the rest of this block, which
                 assumes you've done the insert because you can. */
              _rl_output_some_chars (nfd, lendiff);
              _rl_last_c_pos += lendiff;
            }
          else
            {
              /* We have horizontal scrolling and we are not inserting at
                 the end.  We have invisible characters in this line.  This
                 is a dumb update. */
              _rl_output_some_chars (nfd, temp);
              _rl_last_c_pos += temp;
              return;
            }
          /* Copy (new) chars to screen from first diff to last match. */
          temp = nls - nfd;
          if ((temp - lendiff) > 0)
            {
              _rl_output_some_chars (nfd + lendiff, temp - lendiff);
              _rl_last_c_pos += temp - lendiff;
            }
        }
      else
        {
          /* cannot insert chars, write to EOL */
          _rl_output_some_chars (nfd, temp);
          _rl_last_c_pos += temp;
        }
    }
  else                          /* Delete characters from line. */
    {
      /* If possible and inexpensive to use terminal deletion, then do so. */
      if (term_dc && (2 * temp) >= -lendiff)
        {
          /* If all we're doing is erasing the invisible characters in the
             prompt string, don't bother.  It screws up the assumptions
             about what's on the screen. */
          if (_rl_horizontal_scroll_mode && _rl_last_c_pos == 0 &&
              -lendiff == visible_wrap_offset)
            lendiff = 0;

          if (lendiff)
            delete_chars (-lendiff); /* delete (diff) characters */

          /* Copy (new) chars to screen from first diff to last match */
          temp = nls - nfd;
          if (temp > 0)
            {
              _rl_output_some_chars (nfd, temp);
              _rl_last_c_pos += temp;
            }
        }
      /* Otherwise, print over the existing material. */
      else
        {
          if (temp > 0)
            {
              _rl_output_some_chars (nfd, temp);
              _rl_last_c_pos += temp;
            }
          lendiff = (oe - old) - (ne - new);
          if (_rl_term_autowrap && current_line < inv_botlin)
            space_to_eol (lendiff);
          else
            _rl_clear_to_eol (lendiff);
        }
    }
}

/* Tell the update routines that we have moved onto a new (empty) line. */
int
rl_on_new_line ()
{
  if (visible_line)
    visible_line[0] = '\0';

  _rl_last_c_pos = _rl_last_v_pos = 0;
  _rl_vis_botlin = last_lmargin = 0;
  if (vis_lbreaks)
    vis_lbreaks[0] = vis_lbreaks[1] = 0;
  visible_wrap_offset = 0;
  return 0;
}

/* Actually update the display, period. */
int
rl_forced_update_display ()
{
  if (visible_line)
    {
      register char *temp = visible_line;

      while (*temp)
        *temp++ = '\0';
    }
  rl_on_new_line ();
  forced_display++;
  (*rl_redisplay_function) ();
  return 0;
}

/* Move the cursor from _rl_last_c_pos to NEW, which are buffer indices.
   DATA is the contents of the screen line of interest; i.e., where
   the movement is being done. */
void
_rl_move_cursor_relative (new, data)
     int new;
     char *data;
{
  register int i;

  /* If we don't have to do anything, then return. */
  if (_rl_last_c_pos == new) return;

  /* It may be faster to output a CR, and then move forwards instead
     of moving backwards. */
  /* i == current physical cursor position. */
  i = _rl_last_c_pos - W_OFFSET(_rl_last_v_pos, visible_wrap_offset);
  if (new == 0 || CR_FASTER (new, _rl_last_c_pos) ||
      (_rl_term_autowrap && i == screenwidth))
    {
#if defined (__MSDOS__)
      putc ('\r', rl_outstream);
#else
      tputs (term_cr, 1, _rl_output_character_function);
#endif /* !__MSDOS__ */
      _rl_last_c_pos = 0;
    }

  if (_rl_last_c_pos < new)
    {
      /* Move the cursor forward.  We do it by printing the command
         to move the cursor forward if there is one, else print that
         portion of the output buffer again.  Which is cheaper? */

      /* The above comment is left here for posterity.  It is faster
         to print one character (non-control) than to print a control
         sequence telling the terminal to move forward one character.
         That kind of control is for people who don't know what the
         data is underneath the cursor. */
#if defined (HACK_TERMCAP_MOTION)
      extern char *term_forward_char;

      if (term_forward_char)
        for (i = _rl_last_c_pos; i < new; i++)
          tputs (term_forward_char, 1, _rl_output_character_function);
      else
        for (i = _rl_last_c_pos; i < new; i++)
          putc (data[i], rl_outstream);
#else
      for (i = _rl_last_c_pos; i < new; i++)
        putc (data[i], rl_outstream);
#endif /* HACK_TERMCAP_MOTION */
    }
  else if (_rl_last_c_pos != new)
    _rl_backspace (_rl_last_c_pos - new);
  _rl_last_c_pos = new;
}

/* PWP: move the cursor up or down. */
void
_rl_move_vert (to)
     int to;
{
  register int delta, i;

  if (_rl_last_v_pos == to || to > screenheight)
    return;

#if defined (__GO32__)
  {
    int row, col;

    ScreenGetCursor (&row, &col);
    ScreenSetCursor ((row + to - _rl_last_v_pos), col);
  }
#else /* !__GO32__ */

  if ((delta = to - _rl_last_v_pos) > 0)
    {
      for (i = 0; i < delta; i++)
        putc ('\n', rl_outstream);
      tputs (term_cr, 1, _rl_output_character_function);
      _rl_last_c_pos = 0;
    }
  else
    {                   /* delta < 0 */
      if (term_up && *term_up)
        for (i = 0; i < -delta; i++)
          tputs (term_up, 1, _rl_output_character_function);
    }
#endif /* !__GO32__ */
  _rl_last_v_pos = to;          /* Now TO is here */
}

/* Physically print C on rl_outstream.  This is for functions which know
   how to optimize the display.  Return the number of characters output. */
int
rl_show_char (c)
     int c;
{
  int n = 1;
  if (META_CHAR (c) && (_rl_output_meta_chars == 0))
    {
      fprintf (rl_outstream, "M-");
      n += 2;
      c = UNMETA (c);
    }

#if defined (DISPLAY_TABS)
  if ((CTRL_CHAR (c) && c != '\t') || c == RUBOUT)
#else
  if (CTRL_CHAR (c) || c == RUBOUT)
#endif /* !DISPLAY_TABS */
    {
      fprintf (rl_outstream, "C-");
      n += 2;
      c = CTRL_CHAR (c) ? UNCTRL (c) : '?';
    }

  putc (c, rl_outstream);
  fflush (rl_outstream);
  return n;
}

int
rl_character_len (c, pos)
     register int c, pos;
{
  unsigned char uc;

  uc = (unsigned char)c;

  if (META_CHAR (uc))
    return ((_rl_output_meta_chars == 0) ? 4 : 1);

  if (uc == '\t')
    {
#if defined (DISPLAY_TABS)
      return (((pos | 7) + 1) - pos);
#else
      return (2);
#endif /* !DISPLAY_TABS */
    }

  if (CTRL_CHAR (c) || c == RUBOUT)
    return (2);

  return ((isprint (uc)) ? 1 : 2);
}

/* How to print things in the "echo-area".  The prompt is treated as a
   mini-modeline. */

#if defined (USE_VARARGS)
int
#if defined (PREFER_STDARG)
rl_message (const char *format, ...)
#else
rl_message (va_alist)
     va_dcl
#endif
{
  va_list args;
#if defined (PREFER_VARARGS)
  char *format;
#endif

#if defined (PREFER_STDARG)
  va_start (args, format);
#else
  va_start (args);
  format = va_arg (args, char *);
#endif

  vsprintf (msg_buf, format, args);
  va_end (args);

  rl_display_prompt = msg_buf;
  (*rl_redisplay_function) ();
  return 0;
}
#else /* !USE_VARARGS */
int
rl_message (format, arg1, arg2)
     char *format;
{
  sprintf (msg_buf, format, arg1, arg2);
  rl_display_prompt = msg_buf;
  (*rl_redisplay_function) ();
  return 0;
}
#endif /* !USE_VARARGS */

/* How to clear things from the "echo-area". */
int
rl_clear_message ()
{
  rl_display_prompt = rl_prompt;
  (*rl_redisplay_function) ();
  return 0;
}

int
rl_reset_line_state ()
{
  rl_on_new_line ();

  rl_display_prompt = rl_prompt ? rl_prompt : "";
  forced_display = 1;
  return 0;
}

static char *saved_local_prompt;
static char *saved_local_prefix;
static int saved_last_invisible;
static int saved_visible_length;

void
_rl_save_prompt ()
{
  saved_local_prompt = local_prompt;
  saved_local_prefix = local_prompt_prefix;
  saved_last_invisible = last_invisible;
  saved_visible_length = visible_length;

  local_prompt = local_prompt_prefix = (char *)0;
  last_invisible = visible_length = 0;
}

void
_rl_restore_prompt ()
{
  if (local_prompt)
    free (local_prompt);
  if (local_prompt_prefix)
    free (local_prompt_prefix);

  local_prompt = saved_local_prompt;
  local_prompt_prefix = saved_local_prefix;
  last_invisible = saved_last_invisible;
  visible_length = saved_visible_length;
}

char *
_rl_make_prompt_for_search (pchar)
     int pchar;
{
  int len;
  char *pmt;

  _rl_save_prompt ();

  if (saved_local_prompt == 0)
    {
      len = (rl_prompt && *rl_prompt) ? strlen (rl_prompt) : 0;
      pmt = xmalloc (len + 2);
      if (len)
        strcpy (pmt, rl_prompt);
      pmt[len] = pchar;
      pmt[len+1] = '\0';
    }
  else
    {
      len = *saved_local_prompt ? strlen (saved_local_prompt) : 0;
      pmt = xmalloc (len + 2);
      if (len)
        strcpy (pmt, saved_local_prompt);
      pmt[len] = pchar;
      pmt[len+1] = '\0';
      local_prompt = savestring (pmt);
      last_invisible = saved_last_invisible;
      visible_length = saved_visible_length + 1;
    }
  return pmt;
}

/* Quick redisplay hack when erasing characters at the end of the line. */
void
_rl_erase_at_end_of_line (l)
     int l;
{
  register int i;

  _rl_backspace (l);
  for (i = 0; i < l; i++)
    putc (' ', rl_outstream);
  _rl_backspace (l);
  for (i = 0; i < l; i++)
    visible_line[--_rl_last_c_pos] = '\0';
  rl_display_fixed++;
}

/* Clear to the end of the line.  COUNT is the minimum
   number of character spaces to clear, */
void
_rl_clear_to_eol (count)
     int count;
{
#if !defined (__GO32__)
  if (term_clreol)
    tputs (term_clreol, 1, _rl_output_character_function);
  else if (count)
#endif /* !__GO32__ */
    space_to_eol (count);
}

/* Clear to the end of the line using spaces.  COUNT is the minimum
   number of character spaces to clear, */
static void
space_to_eol (count)
     int count;
{
  register int i;

  for (i = 0; i < count; i++)
   putc (' ', rl_outstream);

  _rl_last_c_pos += count;
}

void
_rl_clear_screen ()
{
#if !defined (__GO32__)
  if (term_clrpag)
    tputs (term_clrpag, 1, _rl_output_character_function);
  else
#endif /* !__GO32__ */
    crlf ();
}

/* Insert COUNT characters from STRING to the output stream. */
static void
insert_some_chars (string, count)
     char *string;
     int count;
{
#if defined (__GO32__)
  int row, col, width;
  char *row_start;

  ScreenGetCursor (&row, &col);
  width = ScreenCols ();
  row_start = ScreenPrimary + (row * width);

  memcpy (row_start + col + count, row_start + col, width - col - count);

  /* Place the text on the screen. */
  _rl_output_some_chars (string, count);
#else /* !_GO32 */

  /* If IC is defined, then we do not have to "enter" insert mode. */
  if (term_IC)
    {
      char *buffer;
      buffer = tgoto (term_IC, 0, count);
      tputs (buffer, 1, _rl_output_character_function);
      _rl_output_some_chars (string, count);
    }
  else
    {
      register int i;

      /* If we have to turn on insert-mode, then do so. */
      if (term_im && *term_im)
        tputs (term_im, 1, _rl_output_character_function);

      /* If there is a special command for inserting characters, then
         use that first to open up the space. */
      if (term_ic && *term_ic)
        {
          for (i = count; i--; )
            tputs (term_ic, 1, _rl_output_character_function);
        }

      /* Print the text. */
      _rl_output_some_chars (string, count);

      /* If there is a string to turn off insert mode, we had best use
         it now. */
      if (term_ei && *term_ei)
        tputs (term_ei, 1, _rl_output_character_function);
    }
#endif /* !__GO32__ */
}

/* Delete COUNT characters from the display line. */
static void
delete_chars (count)
     int count;
{
#if defined (__GO32__)
  int row, col, width;
  char *row_start;

  ScreenGetCursor (&row, &col);
  width = ScreenCols ();
  row_start = ScreenPrimary + (row * width);

  memcpy (row_start + col, row_start + col + count, width - col - count);
  memset (row_start + width - count, 0, count * 2);
#else /* !_GO32 */

  if (count > screenwidth)      /* XXX */
    return;

  if (term_DC && *term_DC)
    {
      char *buffer;
      buffer = tgoto (term_DC, count, count);
      tputs (buffer, count, _rl_output_character_function);
    }
  else
    {
      if (term_dc && *term_dc)
        while (count--)
          tputs (term_dc, 1, _rl_output_character_function);
    }
#endif /* !__GO32__ */
}

void
_rl_update_final ()
{
  int full_lines;

  full_lines = 0;
  /* If the cursor is the only thing on an otherwise-blank last line,
     compensate so we don't print an extra CRLF. */
  if (_rl_vis_botlin && _rl_last_c_pos == 0 &&
        visible_line[vis_lbreaks[_rl_vis_botlin]] == 0)
    {
      _rl_vis_botlin--;
      full_lines = 1;
    }
  _rl_move_vert (_rl_vis_botlin);
  /* If we've wrapped lines, remove the final xterm line-wrap flag. */
  if (full_lines && _rl_term_autowrap && (VIS_LLEN(_rl_vis_botlin) == screenwidth))
    {
      char *last_line;
      last_line = &visible_line[inv_lbreaks[_rl_vis_botlin]];
      _rl_move_cursor_relative (screenwidth - 1, last_line);
      _rl_clear_to_eol (0);
      putc (last_line[screenwidth - 1], rl_outstream);
    }
  _rl_vis_botlin = 0;
  crlf ();
  fflush (rl_outstream);
  rl_display_fixed++;
}

/* Move to the start of the current line. */
static void
cr ()
{
  if (term_cr)
    {
      tputs (term_cr, 1, _rl_output_character_function);
      _rl_last_c_pos = 0;
    }
}

/* Redisplay the current line after a SIGWINCH is received. */
void
_rl_redisplay_after_sigwinch ()
{
  char *t, *oldp, *oldl, *oldlprefix;

  /* Clear the current line and put the cursor at column 0.  Make sure
     the right thing happens if we have wrapped to a new screen line. */
  if (term_cr)
    {
      tputs (term_cr, 1, _rl_output_character_function);
      _rl_last_c_pos = 0;
      if (term_clreol)
        tputs (term_clreol, 1, _rl_output_character_function);
      else
        {
          space_to_eol (screenwidth);
          tputs (term_cr, 1, _rl_output_character_function);
        }
      if (_rl_last_v_pos > 0)
        _rl_move_vert (0);
    }
  else
    crlf ();

  /* Redraw only the last line of a multi-line prompt. */
  t = strrchr (rl_display_prompt, '\n');
  if (t)
    {
      oldp = rl_display_prompt;
      oldl = local_prompt;
      oldlprefix = local_prompt_prefix;
      rl_display_prompt = ++t;
      local_prompt = local_prompt_prefix = (char *)NULL;
      rl_forced_update_display ();
      rl_display_prompt = oldp;
      local_prompt = oldl;
      local_prompt_prefix = oldlprefix;
    }
  else
    rl_forced_update_display ();
}

void
_rl_clean_up_for_exit ()
{
  if (readline_echoing_p)
    {
      _rl_move_vert (_rl_vis_botlin);
      _rl_vis_botlin = 0;
      fflush (rl_outstream);
      rl_restart_output ();
    }
}