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/* Indentation functions.
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   Copyright (C) 1985,86,87,88,93,94,95 Free Software Foundation, Inc.
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This file is part of GNU Emacs.

GNU Emacs is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.

GNU Emacs 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.

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */
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#include <config.h>
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#include "lisp.h"
#include "buffer.h"
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#include "charset.h"
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#include "indent.h"
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#include "frame.h"
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#include "window.h"
#include "termchar.h"
#include "termopts.h"
#include "disptab.h"
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#include "intervals.h"
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#include "region-cache.h"
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/* Indentation can insert tabs if this is non-zero;
   otherwise always uses spaces */
int indent_tabs_mode;

#define min(a, b) ((a) < (b) ? (a) : (b))
#define max(a, b) ((a) > (b) ? (a) : (b))

#define CR 015

/* These three values memoize the current column to avoid recalculation */
/* Some things in set last_known_column_point to -1
  to mark the memoized value as invalid */
/* Last value returned by current_column */
int last_known_column;
/* Value of point when current_column was called */
int last_known_column_point;
/* Value of MODIFF when current_column was called */
int last_known_column_modified;

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static int current_column_1 ();

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/* Cache of beginning of line found by the last call of
   current_column. */
int current_column_bol_cache;

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/* Get the display table to use for the current buffer.  */

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struct Lisp_Char_Table *
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buffer_display_table ()
{
  Lisp_Object thisbuf;

  thisbuf = current_buffer->display_table;
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  if (DISP_TABLE_P (thisbuf))
    return XCHAR_TABLE (thisbuf);
  if (DISP_TABLE_P (Vstandard_display_table))
    return XCHAR_TABLE (Vstandard_display_table);
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  return 0;
}
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/* Width run cache considerations.  */

/* Return the width of character C under display table DP.  */
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static int
character_width (c, dp)
     int c;
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     struct Lisp_Char_Table *dp;
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{
  Lisp_Object elt;

  /* These width computations were determined by examining the cases
     in display_text_line.  */

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  /* Everything can be handled by the display table, if it's
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     present and the element is right.  */
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  if (dp && (elt = DISP_CHAR_VECTOR (dp, c), VECTORP (elt)))
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    return XVECTOR (elt)->size;

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  /* Some characters are special.  */
  if (c == '\n' || c == '\t' || c == '\015')
    return 0;

  /* Printing characters have width 1.  */
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  else if (c >= 040 && c < 0177)
    return 1;

  /* Everybody else (control characters, metacharacters) has other
     widths.  We could return their actual widths here, but they
     depend on things like ctl_arrow and crud like that, and they're
     not very common at all.  So we'll just claim we don't know their
     widths.  */
  else
    return 0;
}

/* Return true iff the display table DISPTAB specifies the same widths
   for characters as WIDTHTAB.  We use this to decide when to
   invalidate the buffer's width_run_cache.  */
int
disptab_matches_widthtab (disptab, widthtab)
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     struct Lisp_Char_Table *disptab;
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     struct Lisp_Vector *widthtab;
{
  int i;

  if (widthtab->size != 256)
    abort ();

  for (i = 0; i < 256; i++)
    if (character_width (i, disptab)
        != XFASTINT (widthtab->contents[i]))
      return 0;

  return 1;
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}
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/* Recompute BUF's width table, using the display table DISPTAB.  */
void
recompute_width_table (buf, disptab)
     struct buffer *buf;
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     struct Lisp_Char_Table *disptab;
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{
  int i;
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  struct Lisp_Vector *widthtab;
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  if (!VECTORP (buf->width_table))
    buf->width_table = Fmake_vector (make_number (256), make_number (0));
  widthtab = XVECTOR (buf->width_table);
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  if (widthtab->size != 256)
    abort ();

  for (i = 0; i < 256; i++)
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    XSETFASTINT (widthtab->contents[i], character_width (i, disptab));
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}

/* Allocate or free the width run cache, as requested by the current
   state of current_buffer's cache_long_line_scans variable.  */
static void
width_run_cache_on_off ()
{
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  if (NILP (current_buffer->cache_long_line_scans)
      /* And, for the moment, this feature doesn't work on multibyte
         characters.  */
      || !NILP (current_buffer->enable_multibyte_characters))
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    {
      /* It should be off.  */
      if (current_buffer->width_run_cache)
        {
          free_region_cache (current_buffer->width_run_cache);
          current_buffer->width_run_cache = 0;
          current_buffer->width_table = Qnil;
        }
    }
  else
    {
      /* It should be on.  */
      if (current_buffer->width_run_cache == 0)
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        {
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          current_buffer->width_run_cache = new_region_cache ();
          recompute_width_table (current_buffer, buffer_display_table ());
        }
    }
}

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/* Skip some invisible characters starting from POS.
   This includes characters invisible because of text properties
   and characters invisible because of overlays.

   If position POS is followed by invisible characters,
   skip some of them and return the position after them.
   Otherwise return POS itself.

   Set *NEXT_BOUNDARY_P to the next position at which
   it will be necessary to call this function again.

   Don't scan past TO, and don't set *NEXT_BOUNDARY_P
   to a value greater than TO.

   If WINDOW is non-nil, and this buffer is displayed in WINDOW,
   take account of overlays that apply only in WINDOW.

   We don't necessarily skip all the invisible characters after POS
   because that could take a long time.  We skip a reasonable number
   which can be skipped quickly.  If there might be more invisible
   characters immediately following, then *NEXT_BOUNDARY_P
   will equal the return value.  */

static int
skip_invisible (pos, next_boundary_p, to, window)
     int pos;
     int *next_boundary_p;
     int to;
     Lisp_Object window;
{
  Lisp_Object prop, position, end, overlay_limit, proplimit;
  Lisp_Object buffer;

  XSETFASTINT (position, pos);
  XSETBUFFER (buffer, current_buffer);

  /* Give faster response for overlay lookup near POS.  */
  recenter_overlay_lists (current_buffer, pos);

  /* We must not advance farther than the next overlay change.
     The overlay change might change the invisible property;
     or there might be overlay strings to be displayed there.  */
  overlay_limit = Fnext_overlay_change (position);
  /* As for text properties, this gives a lower bound
     for where the invisible text property could change.  */
  proplimit = Fnext_property_change (position, buffer, Qt);
  if (XFASTINT (overlay_limit) < XFASTINT (proplimit))
    proplimit = overlay_limit;
  /* PROPLIMIT is now a lower bound for the next change
     in invisible status.  If that is plenty far away,
     use that lower bound.  */
  if (XFASTINT (proplimit) > pos + 100 || XFASTINT (proplimit) >= to)
    *next_boundary_p = XFASTINT (proplimit);
  /* Otherwise, scan for the next `invisible' property change.  */
  else
    {
      /* Don't scan terribly far.  */
      XSETFASTINT (proplimit, min (pos + 100, to));
      /* No matter what. don't go past next overlay change.  */
      if (XFASTINT (overlay_limit) < XFASTINT (proplimit))
	proplimit = overlay_limit;
      end = Fnext_single_property_change (position, Qinvisible,
					  buffer, proplimit);
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      /* Don't put the boundary in the middle of multibyte form if
         there is no actual property change.  */
      if (end == pos + 100
	  && !NILP (current_buffer->enable_multibyte_characters)
	  && end < ZV)
	while (pos < end && !CHAR_HEAD_P (POS_ADDR (end)))
	  end--;
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      *next_boundary_p = XFASTINT (end);
    }
  /* if the `invisible' property is set, we can skip to
     the next property change */
  if (!NILP (window) && EQ (XWINDOW (window)->buffer, buffer))
    prop = Fget_char_property (position, Qinvisible, window);
  else
    prop = Fget_char_property (position, Qinvisible, buffer);
  if (TEXT_PROP_MEANS_INVISIBLE (prop))
    return *next_boundary_p;
  return pos;
}
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DEFUN ("current-column", Fcurrent_column, Scurrent_column, 0, 0, 0,
  "Return the horizontal position of point.  Beginning of line is column 0.\n\
This is calculated by adding together the widths of all the displayed\n\
representations of the character between the start of the previous line\n\
and point.  (eg control characters will have a width of 2 or 4, tabs\n\
will have a variable width)\n\
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Ignores finite width of frame, which means that this function may return\n\
values greater than (frame-width).\n\
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Whether the line is visible (if `selective-display' is t) has no effect;\n\
however, ^M is treated as end of line when `selective-display' is t.")
  ()
{
  Lisp_Object temp;
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  XSETFASTINT (temp, current_column ());
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  return temp;
}

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/* Cancel any recorded value of the horizontal position.  */

invalidate_current_column ()
{
  last_known_column_point = 0;
}

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int
current_column ()
{
  register int col;
  register unsigned char *ptr, *stop;
  register int tab_seen;
  int post_tab;
  register int c;
  register int tab_width = XINT (current_buffer->tab_width);
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  int ctl_arrow = !NILP (current_buffer->ctl_arrow);
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  register struct Lisp_Char_Table *dp = buffer_display_table ();
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  int stopchar;

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  if (PT == last_known_column_point
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      && MODIFF == last_known_column_modified)
    return last_known_column;

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  /* If the buffer has overlays, text properties, or multibyte, 
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     use a more general algorithm.  */
  if (BUF_INTERVALS (current_buffer)
      || !NILP (current_buffer->overlays_before)
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      || !NILP (current_buffer->overlays_after)
      || !NILP (current_buffer->enable_multibyte_characters))
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    return current_column_1 (PT);
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  /* Scan backwards from point to the previous newline,
     counting width.  Tab characters are the only complicated case.  */

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  /* Make a pointer for decrementing through the chars before point.  */
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  ptr = POS_ADDR (PT - 1) + 1;
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  /* Make a pointer to where consecutive chars leave off,
     going backwards from point.  */
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  if (PT == BEGV)
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    stop = ptr;
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  else if (PT <= GPT || BEGV > GPT)
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    stop = BEGV_ADDR;
  else
    stop = GAP_END_ADDR;

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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;
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  col = 0, tab_seen = 0, post_tab = 0;

  while (1)
    {
      if (ptr == stop)
	{
	  /* We stopped either for the beginning of the buffer
	     or for the gap.  */
	  if (ptr == BEGV_ADDR)
	    break;
	  /* It was the gap.  Jump back over it.  */
	  stop = BEGV_ADDR;
	  ptr = GPT_ADDR;
	  /* Check whether that brings us to beginning of buffer.  */
	  if (BEGV >= GPT) break;
	}

      c = *--ptr;
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      if (dp != 0 && VECTORP (DISP_CHAR_VECTOR (dp, c)))
	col += XVECTOR (DISP_CHAR_VECTOR (dp, c))->size;
      else if (c >= 040 && c < 0177)
	col++;
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      else if (c == '\n')
	break;
      else if (c == '\r' && EQ (current_buffer->selective_display, Qt))
	break;
      else if (c == '\t')
	{
	  if (tab_seen)
	    col = ((col + tab_width) / tab_width) * tab_width;

	  post_tab += col;
	  col = 0;
	  tab_seen = 1;
	}
      else
	col += (ctl_arrow && c < 0200) ? 2 : 4;
    }

  if (tab_seen)
    {
      col = ((col + tab_width) / tab_width) * tab_width;
      col += post_tab;
    }

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  if (ptr == BEGV_ADDR)
    current_column_bol_cache = BEGV;
  else
    current_column_bol_cache = PTR_CHAR_POS ((ptr+1));
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  last_known_column = col;
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  last_known_column_point = PT;
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  last_known_column_modified = MODIFF;

  return col;
}

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/* Return the column number of position POS
   by scanning forward from the beginning of the line.
   This function handles characters that are invisible
   due to text properties or overlays.  */

static int
current_column_1 (pos)
     int pos;
{
  register int tab_width = XINT (current_buffer->tab_width);
  register int ctl_arrow = !NILP (current_buffer->ctl_arrow);
  register struct Lisp_Char_Table *dp = buffer_display_table ();

  /* Start the scan at the beginning of this line with column number 0.  */
  register int col = 0;
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  int scan = current_column_bol_cache = find_next_newline (pos, -1);
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  int next_boundary = scan;
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  int multibyte = !NILP (current_buffer->enable_multibyte_characters);
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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;

  /* Scan forward to the target position.  */
  while (scan < pos)
    {
      int c;

      /* Occasionally we may need to skip invisible text.  */
      while (scan == next_boundary)
	{
	  /* This updates NEXT_BOUNDARY to the next place
	     where we might need to skip more invisible text.  */
	  scan = skip_invisible (scan, &next_boundary, pos, Qnil);
	  if (scan >= pos)
	    goto endloop;
	}

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      c = FETCH_BYTE (scan);
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      if (dp != 0 && VECTORP (DISP_CHAR_VECTOR (dp, c)))
	{
	  col += XVECTOR (DISP_CHAR_VECTOR (dp, c))->size;
	  scan++;
	  continue;
	}
      if (c == '\n')
	break;
      if (c == '\r' && EQ (current_buffer->selective_display, Qt))
	break;
      scan++;
      if (c == '\t')
	{
	  int prev_col = col;
	  col += tab_width;
	  col = col / tab_width * tab_width;
	}
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      else if (multibyte && BASE_LEADING_CODE_P (c))
	{
	  scan--;
	  /* Start of multi-byte form.  */
	  if (c == LEADING_CODE_COMPOSITION)
	    {
	      unsigned char *ptr = POS_ADDR (scan);

	      int cmpchar_id = str_cmpchar_id (ptr, next_boundary - scan);
	      if (cmpchar_id >= 0)
		{
		  scan += cmpchar_table[cmpchar_id]->len,
		  col += cmpchar_table[cmpchar_id]->width;
		}
	      else
		{		/* invalid composite character */
		  scan++;
		  col += 4;
		}
	    }
	  else
	    {
	      /* Here, we check that the following bytes are valid
		 constituents of multi-byte form.  */
	      int len = BYTES_BY_CHAR_HEAD (c), i;

	      for (i = 1, scan++; i < len; i++, scan++)
		/* We don't need range checking for PTR because there
		   are anchors (`\0') at GAP and Z.  */
		if (CHAR_HEAD_P (POS_ADDR (scan))) break;
	      if (i < len)
		col += 4, scan -= i - 1;
	      else
		col += WIDTH_BY_CHAR_HEAD (c);
	    }
	}
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      else if (ctl_arrow && (c < 040 || c == 0177))
        col += 2;
      else if (c < 040 || c >= 0177)
        col += 4;
      else
	col++;
    }
 endloop:

  last_known_column = col;
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  last_known_column_point = PT;
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  last_known_column_modified = MODIFF;

  return col;
}

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/* Return the width in columns of the part of STRING from BEG to END.
   If BEG is nil, that stands for the beginning of STRING.
   If END is nil, that stands for the end of STRING.  */

static int
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string_display_width (string, beg, end)
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     Lisp_Object string, beg, end;
{
  register int col;
  register unsigned char *ptr, *stop;
  register int tab_seen;
  int post_tab;
  register int c;
  register int tab_width = XINT (current_buffer->tab_width);
  int ctl_arrow = !NILP (current_buffer->ctl_arrow);
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  register struct Lisp_Char_Table *dp = buffer_display_table ();
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  int b, e;

  if (NILP (end))
    e = XSTRING (string)->size;
  else
    {
      CHECK_NUMBER (end, 0);
      e = XINT (end);
    }

  if (NILP (beg))
    b = 0;
  else
    {
      CHECK_NUMBER (beg, 0);
      b = XINT (beg);
    }

  /* Make a pointer for decrementing through the chars before point.  */
  ptr = XSTRING (string)->data + e;
  /* Make a pointer to where consecutive chars leave off,
     going backwards from point.  */
  stop = XSTRING (string)->data + b;

  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;

  col = 0, tab_seen = 0, post_tab = 0;

  while (1)
    {
      if (ptr == stop)
	break;

      c = *--ptr;
      if (dp != 0 && VECTORP (DISP_CHAR_VECTOR (dp, c)))
	col += XVECTOR (DISP_CHAR_VECTOR (dp, c))->size;
      else if (c >= 040 && c < 0177)
	col++;
      else if (c == '\n')
	break;
      else if (c == '\t')
	{
	  if (tab_seen)
	    col = ((col + tab_width) / tab_width) * tab_width;

	  post_tab += col;
	  col = 0;
	  tab_seen = 1;
	}
      else
	col += (ctl_arrow && c < 0200) ? 2 : 4;
    }

  if (tab_seen)
    {
      col = ((col + tab_width) / tab_width) * tab_width;
      col += post_tab;
    }

  return col;
}

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DEFUN ("indent-to", Findent_to, Sindent_to, 1, 2, "NIndent to column: ",
  "Indent from point with tabs and spaces until COLUMN is reached.\n\
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Optional second argument MININUM says always do at least MININUM spaces\n\
even if that goes past COLUMN; by default, MININUM is zero.")
  (column, minimum)
     Lisp_Object column, minimum;
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{
  int mincol;
  register int fromcol;
  register int tab_width = XINT (current_buffer->tab_width);

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  CHECK_NUMBER (column, 0);
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  if (NILP (minimum))
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    XSETFASTINT (minimum, 0);
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  CHECK_NUMBER (minimum, 1);

  fromcol = current_column ();
  mincol = fromcol + XINT (minimum);
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  if (mincol < XINT (column)) mincol = XINT (column);
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  if (fromcol == mincol)
    return make_number (mincol);

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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;
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  if (indent_tabs_mode)
    {
      Lisp_Object n;
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      XSETFASTINT (n, mincol / tab_width - fromcol / tab_width);
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      if (XFASTINT (n) != 0)
	{
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	  Finsert_char (make_number ('\t'), n, Qt);
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	  fromcol = (mincol / tab_width) * tab_width;
	}
    }

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  XSETFASTINT (column, mincol - fromcol);
  Finsert_char (make_number (' '), column, Qt);
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  last_known_column = mincol;
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  last_known_column_point = PT;
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  last_known_column_modified = MODIFF;

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  XSETINT (column, mincol);
  return column;
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}
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DEFUN ("current-indentation", Fcurrent_indentation, Scurrent_indentation,
  0, 0, 0,
  "Return the indentation of the current line.\n\
This is the horizontal position of the character\n\
following any initial whitespace.")
  ()
{
  Lisp_Object val;

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  XSETFASTINT (val, position_indentation (find_next_newline (PT, -1)));
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  return val;
}

position_indentation (pos)
     register int pos;
{
  register int column = 0;
  register int tab_width = XINT (current_buffer->tab_width);
  register unsigned char *p;
  register unsigned char *stop;
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  unsigned char *start;
  int next_boundary = pos;
  int ceiling = pos;
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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;
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  p = POS_ADDR (pos);
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  /* STOP records the value of P at which we will need
     to think about the gap, or about invisible text,
     or about the end of the buffer.  */
  stop = p;
  /* START records the starting value of P.  */
  start = p;
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  while (1)
    {
      while (p == stop)
	{
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	  int stop_pos;

	  /* If we have updated P, set POS to match.
	     The first time we enter the loop, POS is already right.  */
	  if (p != start)
	    pos = PTR_CHAR_POS (p);
	  /* Consider the various reasons STOP might have been set here.  */
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	  if (pos == ZV)
	    return column;
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	  if (pos == next_boundary)
	    pos = skip_invisible (pos, &next_boundary, ZV, Qnil);
	  if (pos >= ceiling)
	    ceiling = BUFFER_CEILING_OF (pos) + 1;
	  /* Compute the next place we need to stop and think,
	     and set STOP accordingly.  */
	  stop_pos = min (ceiling, next_boundary);
	  /* The -1 and +1 arrange to point at the first byte of gap
	     (if STOP_POS is the position of the gap)
	     rather than at the data after the gap.  */
	     
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	  stop = POS_ADDR (stop_pos - 1) + 1;
	  p = POS_ADDR (pos);
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	}
      switch (*p++)
	{
	case ' ':
	  column++;
	  break;
	case '\t':
	  column += tab_width - column % tab_width;
	  break;
	default:
	  return column;
	}
    }
}
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/* Test whether the line beginning at POS is indented beyond COLUMN.
   Blank lines are treated as if they had the same indentation as the
   preceding line.  */
int
indented_beyond_p (pos, column)
     int pos, column;
{
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  while (pos > BEGV && FETCH_BYTE (pos) == '\n')
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    pos = find_next_newline_no_quit (pos - 1, -1);
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  return (position_indentation (pos) >= column);
}
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DEFUN ("move-to-column", Fmove_to_column, Smove_to_column, 1, 2, "p",
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  "Move point to column COLUMN in the current line.\n\
The column of a character is calculated by adding together the widths\n\
as displayed of the previous characters in the line.\n\
This function ignores line-continuation;\n\
there is no upper limit on the column number a character can have\n\
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and horizontal scrolling has no effect.\n\
\n\
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If specified column is within a character, point goes after that character.\n\
If it's past end of line, point goes to end of line.\n\n\
A non-nil second (optional) argument FORCE means, if the line\n\
is too short to reach column COLUMN then add spaces/tabs to get there,\n\
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and if COLUMN is in the middle of a tab character, change it to spaces.\n\
\n\
The return value is the current column.")
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  (column, force)
     Lisp_Object column, force;
{
  register int pos;
  register int col = current_column ();
  register int goal;
  register int end;
  register int tab_width = XINT (current_buffer->tab_width);
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  register int ctl_arrow = !NILP (current_buffer->ctl_arrow);
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  register struct Lisp_Char_Table *dp = buffer_display_table ();
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  register int multibyte = !NILP (current_buffer->enable_multibyte_characters);
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  Lisp_Object val;
  int prev_col;
  int c;

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  int next_boundary;

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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;
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  CHECK_NATNUM (column, 0);
  goal = XINT (column);

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  pos = PT;
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  end = ZV;
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  next_boundary = pos;
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  /* If we're starting past the desired column,
     back up to beginning of line and scan from there.  */
  if (col > goal)
    {
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      end = pos;
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      pos = current_column_bol_cache;
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      col = 0;
    }

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  while (pos < end)
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    {
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      while (pos == next_boundary)
	{
	  pos = skip_invisible (pos, &next_boundary, end, Qnil);
	  if (pos >= end)
	    goto endloop;
	}

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      /* Test reaching the goal column.  We do this after skipping
	 invisible characters, so that we put point before the
	 character on which the cursor will appear.  */
      if (col >= goal)
	break;

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      c = FETCH_BYTE (pos);
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      if (dp != 0 && VECTORP (DISP_CHAR_VECTOR (dp, c)))
	{
	  col += XVECTOR (DISP_CHAR_VECTOR (dp, c))->size;
	  pos++;
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	  continue;
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	}
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      if (c == '\n')
	break;
      if (c == '\r' && EQ (current_buffer->selective_display, Qt))
	break;
      pos++;
      if (c == '\t')
	{
	  prev_col = col;
	  col += tab_width;
	  col = col / tab_width * tab_width;
	}
      else if (ctl_arrow && (c < 040 || c == 0177))
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        col += 2;
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      else if (c < 040 || c == 0177)
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        col += 4;
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      else if (c < 0177)
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	col++;
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      else if (multibyte && BASE_LEADING_CODE_P (c))
	{
	  /* Start of multi-byte form.  */
	  unsigned char *ptr;

	  pos--;		/* rewind to the character head */
	  ptr = POS_ADDR (pos);
	  if (c == LEADING_CODE_COMPOSITION)
	    {
	      int cmpchar_id = str_cmpchar_id (ptr, end - pos);

	      if (cmpchar_id >= 0)
		{
		  col += cmpchar_table[cmpchar_id]->width;
		  pos += cmpchar_table[cmpchar_id]->len;
		}
	      else
		{		/* invalid composite character */
		  col += 4;
		  pos++;
		}
	    }
	  else
	    {
	      /* Here, we check that the following bytes are valid
		 constituents of multi-byte form.  */
	      int len = BYTES_BY_CHAR_HEAD (c), i;

	      for (i = 1, ptr++; i < len; i++, ptr++)
		/* We don't need range checking for PTR because there
		   are anchors (`\0') both at GPT and Z.  */
		if (CHAR_HEAD_P (ptr)) break;
	      if (i < len)
		col += 4, pos++;
	      else
		col += WIDTH_BY_CHAR_HEAD (c), pos += i;
	    }
	}
      else
	col += 4;
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    }
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 endloop:
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  SET_PT (pos);

  /* If a tab char made us overshoot, change it to spaces
     and scan through it again.  */
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  if (!NILP (force) && col > goal && c == '\t' && prev_col < goal)
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    {
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      int old_point;

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      del_range (PT - 1, PT);
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      Findent_to (make_number (goal), Qnil);
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      old_point = PT;
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      Findent_to (make_number (col), Qnil);
      SET_PT (old_point);
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      /* Set the last_known... vars consistently.  */
      col = goal;
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    }

  /* If line ends prematurely, add space to the end.  */
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  if (col < goal && !NILP (force))
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    Findent_to (make_number (col = goal), Qnil);
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  last_known_column = col;
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  last_known_column_point = PT;
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  last_known_column_modified = MODIFF;

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  XSETFASTINT (val, col);
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  return val;
}

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/* compute_motion: compute buffer posn given screen posn and vice versa */

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struct position val_compute_motion;

/* Scan the current buffer forward from offset FROM, pretending that
   this is at line FROMVPOS, column FROMHPOS, until reaching buffer
   offset TO or line TOVPOS, column TOHPOS (whichever comes first),
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   and return the ending buffer position and screen location.  If we
   can't hit the requested column exactly (because of a tab or other
   multi-column character), overshoot.
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   DID_MOTION is 1 if FROMHPOS has already accounted for overlay strings
   at FROM.  This is the case if FROMVPOS and FROMVPOS came from an
   earlier call to compute_motion.  The other common case is that FROMHPOS
   is zero and FROM is a position that "belongs" at column zero, but might
   be shifted by overlay strings; in this case DID_MOTION should be 0.

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   WIDTH is the number of columns available to display text;
   compute_motion uses this to handle continuation lines and such.
   HSCROLL is the number of columns not being displayed at the left
   margin; this is usually taken from a window's hscroll member.
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   TAB_OFFSET is the number of columns of the first tab that aren't
   being displayed, perhaps because of a continuation line or
   something.
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   compute_motion returns a pointer to a struct position.  The bufpos
   member gives the buffer position at the end of the scan, and hpos
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   and vpos give its cartesian location.  prevhpos is the column at
   which the character before bufpos started, and contin is non-zero
   if we reached the current line by continuing the previous.

   Note that FROMHPOS and TOHPOS should be expressed in real screen
   columns, taking HSCROLL and the truncation glyph at the left margin
   into account.  That is, beginning-of-line moves you to the hpos
   -HSCROLL + (HSCROLL > 0).
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   For example, to find the buffer position of column COL of line LINE
   of a certain window, pass the window's starting location as FROM
   and the window's upper-left coordinates as FROMVPOS and FROMHPOS.
   Pass the buffer's ZV as TO, to limit the scan to the end of the
   visible section of the buffer, and pass LINE and COL as TOVPOS and
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   TOHPOS.
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   When displaying in window w, a typical formula for WIDTH is:

	window_width - 1
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	 - (has_vertical_scroll_bars
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	    ? FRAME_SCROLL_BAR_COLS (XFRAME (window->frame))
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	    : (window_width + window_left != frame_width))
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	where
	  window_width is XFASTINT (w->width),
	  window_left is XFASTINT (w->left),
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	  has_vertical_scroll_bars is
	    FRAME_HAS_VERTICAL_SCROLL_BARS (XFRAME (WINDOW_FRAME (window)))
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	  and frame_width = FRAME_WIDTH (XFRAME (window->frame))
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   Or you can let window_internal_width do this all for you, and write:
	window_internal_width (w) - 1
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   The `-1' accounts for the continuation-line backslashes; the rest
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   accounts for window borders if the window is split horizontally, and
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   the scroll bars if they are turned on.  */
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struct position *
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compute_motion (from, fromvpos, fromhpos, did_motion, to, tovpos, tohpos, width, hscroll, tab_offset, win)
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     int from, fromvpos, fromhpos, to, tovpos, tohpos;
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     int did_motion;
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     register int width;
     int hscroll, tab_offset;
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     struct window *win;
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{
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  register int hpos = fromhpos;
  register int vpos = fromvpos;

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  register int pos;
  register int c;
  register int tab_width = XFASTINT (current_buffer->tab_width);
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  register int ctl_arrow = !NILP (current_buffer->ctl_arrow);
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  register struct Lisp_Char_Table *dp = window_display_table (win);
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  int selective
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    = (INTEGERP (current_buffer->selective_display)
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       ? XINT (current_buffer->selective_display)
       : !NILP (current_buffer->selective_display) ? -1 : 0);
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  int prev_hpos = 0;
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  int selective_rlen
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    = (selective && dp && VECTORP (DISP_INVIS_VECTOR (dp))
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       ? XVECTOR (DISP_INVIS_VECTOR (dp))->size : 0);
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  /* The next location where the `invisible' property changes, or an
     overlay starts or ends.  */
  int next_boundary = from;
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  /* For computing runs of characters with similar widths.
     Invariant: width_run_width is zero, or all the characters
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     from width_run_start to width_run_end have a fixed width of
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     width_run_width.  */
  int width_run_start = from;
  int width_run_end   = from;
  int width_run_width = 0;
  Lisp_Object *width_table;
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  Lisp_Object buffer;
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  /* The next buffer pos where we should consult the width run cache. */
  int next_width_run = from;
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  Lisp_Object window;
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  int multibyte = !NILP (current_buffer->enable_multibyte_characters);
  int wide_column = 0;		/* Set to 1 when a previous character
				   is wide-colomn.  */
  int prev_pos;			/* Previous buffer position.  */
  int contin_hpos;		/* HPOS of last column of continued line.  */
  int prev_tab_offset;		/* Previous tab offset.  */

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  XSETBUFFER (buffer, current_buffer);
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  XSETWINDOW (window, win);
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  width_run_cache_on_off ();
  if (dp == buffer_display_table ())
    width_table = (VECTORP (current_buffer->width_table)
                   ? XVECTOR (current_buffer->width_table)->contents
                   : 0);
  else
    /* If the window has its own display table, we can't use the width
       run cache, because that's based on the buffer's display table.  */
    width_table = 0;

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  if (tab_width <= 0 || tab_width > 1000) tab_width = 8;
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  pos = prev_pos = from;
  contin_hpos = 0;
  prev_tab_offset = tab_offset;
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  while (1)
    {
      while (pos == next_boundary)
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	{
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	  int newpos;

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	  /* If the caller says that the screen position came from an earlier
	     call to compute_motion, then we've already accounted for the
	     overlay strings at point.  This is only true the first time
	     through, so clear the flag after testing it.  */
	  if (!did_motion)
	    /* We need to skip past the overlay strings.  Currently those
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	       strings must not contain TAB;
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	       if we want to relax that restriction, something will have
	       to be changed here.  */
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	    {
	      unsigned char *ovstr;
	      int ovlen = overlay_strings (pos, win, &ovstr);
	      hpos += (multibyte ? strwidth (ovstr, ovlen) : ovlen);
	    }
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	  did_motion = 0;

	  if (pos >= to)
	    break;
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	  /* Advance POS past invisible characters
	     (but not necessarily all that there are here),
	     and store in next_boundary the next position where
	     we need to call skip_invisible.  */
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	  newpos = skip_invisible (pos, &next_boundary, to, window);

	  if (newpos >= to)
	    goto after_loop;

	  pos = newpos;
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	}
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      /* Handle right margin.  */
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      /* Note on a wide-column character.

	 Characters are classified into the following three categories
	 according to the width (columns occupied on screen).

	 (1) single-column character: ex. `a'
	 (2) multi-column character: ex. `^A', TAB, `\033'
	 (3) wide-column character: ex. Japanese character, Chinese character
	     (In the following example, `W_' stands for them.)

	 Multi-column characters can be divided around the right margin,
	 but wide-column characters cannot.

	 NOTE:

	 (*) The cursor is placed on the next character after the point.

	     ----------
	     abcdefghi\
	     j        ^---- next after the point
	     ^---  next char. after the point.
	     ----------
	              In case of sigle-column character

	     ----------
	     abcdefgh\\
	     033     ^----  next after the point, next char. after the point.
	     ----------
	              In case of multi-column character

	     ----------
	     abcdefgh\\
	     W_      ^---- next after the point
	     ^----  next char. after the point.
	     ----------
	              In case of wide-column character 

	 The problem here is continuation at a wide-column character.
	 In this case, the line may shorter less than WIDTH.
	 And we find the continuation AFTER it occurs.

       */

      if (hpos > width)
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	{
	  if (hscroll
	      || (truncate_partial_width_windows
		  && width + 1 < FRAME_WIDTH (XFRAME (WINDOW_FRAME (win))))
	      || !NILP (current_buffer->truncate_lines))
	    {
	      /* Truncating: skip to newline.  */
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	      if (pos <= to)  /* This IF is needed because we may past TO */
		pos = find_before_next_newline (pos, to, 1);
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	      hpos = width;
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	      /* If we just skipped next_boundary,
		 loop around in the main while
		 and handle it.  */
	      if (pos >= next_boundary)
		next_boundary = pos + 1;
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	      prev_hpos = width;
	      prev_tab_offset = tab_offset;
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	    }
	  else
	    {
	      /* Continuing.  */
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	      /* Remember the previous value.  */
	      prev_tab_offset = tab_offset;

	      if (wide_column)
		{
		  hpos -= prev_hpos;
		  tab_offset += prev_hpos;
		}
	      else
		{
		  tab_offset += width;
		  hpos -= width;
		}
	      vpos++;
	      contin_hpos = prev_hpos;
	      prev_hpos = 0;
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	    }
	}

      /* Stop if past the target buffer position or screen position.  */
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      if (pos > to)
	{
	  /* Go back to the previous position.  */
	  pos = prev_pos;
	  hpos = prev_hpos;
	  tab_offset = prev_tab_offset;

	  /* NOTE on contin_hpos, hpos, and prev_hpos.

	     ----------
	     abcdefgh\\
	     W_      ^----  contin_hpos
	     | ^-----  hpos
	     \---- prev_hpos
	     ----------
	   */

	  if (contin_hpos && prev_hpos == 0
	      && contin_hpos < width && !wide_column)
	    {
	      /* Line breaking occurs in the middle of multi-column
		 character.  Go back to previous line.  */
	      hpos = contin_hpos;
	      vpos = vpos - 1;
	    }
	  else if (c == '\n')
	    /* If previous character is NEWLINE,
	       set VPOS back to previous line */
	    vpos = vpos - 1;
	  break;
	}

      if (vpos > tovpos || vpos == tovpos && hpos >= tohpos)
	{
	  if (contin_hpos && prev_hpos == 0
	      && (contin_hpos == width || wide_column))
	    { /* Line breaks because we can't put the character at the
		 previous line any more.  It is not the multi-column
		 character continued in middle.  Go back to previous
		 buffer position, screen position, and set tab offset
		 to previous value.  It's the beginning of the
		 line.  */
	      pos = prev_pos;
	      hpos = prev_hpos;
	      tab_offset = prev_tab_offset;
	    }
	  break;
	}
      if (pos == ZV) /* We cannot go beyond ZV.  Stop here. */
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	break;

      prev_hpos = hpos;
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      prev_pos = pos;
      wide_column = 0;
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      /* Consult the width run cache to see if we can avoid inspecting
         the text character-by-character.  */
      if (current_buffer->width_run_cache && pos >= next_width_run)
        {
          int run_end;
          int common_width
            = region_cache_forward (current_buffer,
                                    current_buffer->width_run_cache,
                                    pos, &run_end);

          /* A width of zero means the character's width varies (like
             a tab), is meaningless (like a newline), or we just don't
             want to skip over it for some other reason.  */
          if (common_width != 0)
            {
              int run_end_hpos;

              /* Don't go past the final buffer posn the user
                 requested.  */
              if (run_end > to)
                run_end = to;

              run_end_hpos = hpos + (run_end - pos) * common_width;

              /* Don't go past the final horizontal position the user
                 requested.  */
              if (vpos == tovpos && run_end_hpos > tohpos)
                {
                  run_end      = pos + (tohpos - hpos) / common_width;
                  run_end_hpos = hpos + (run_end - pos) * common_width;
                }
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              /* Don't go past the margin.  */
              if (run_end_hpos >= width)
                {
                  run_end      = pos + (width  - hpos) / common_width;
                  run_end_hpos = hpos + (run_end - pos) * common_width;
                }

              hpos = run_end_hpos;
              if (run_end > pos)
                prev_hpos = hpos - common_width;
              pos = run_end;
            }

          next_width_run = run_end + 1;
        }

      /* We have to scan the text character-by-character.  */
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      else
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	{
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	  c = FETCH_BYTE (pos);
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	  pos++;
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	  /* Perhaps add some info to the width_run_cache.  */
	  if (current_buffer->width_run_cache)
	    {
	      /* Is this character part of the current run?  If so, extend
		 the run.  */
	      if (pos - 1 == width_run_end
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		  && XFASTINT (width_table[c]) == width_run_width)
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		width_run_end = pos;

	      /* The previous run is over, since this is a character at a
		 different position, or a different width.  */
	      else
		{
		  /* Have we accumulated a run to put in the cache?
		     (Currently, we only cache runs of width == 1).  */
		  if (width_run_start < width_run_end
		      && width_run_width == 1)
		    know_region_cache (current_buffer,
				       current_buffer->width_run_cache,
				       width_run_start, width_run_end);

		  /* Start recording a new width run.  */
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		  width_run_width = XFASTINT (width_table[c]);
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		  width_run_start = pos - 1;
		  width_run_end = pos;
		}
	    }
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	  if (dp != 0 && VECTORP (DISP_CHAR_VECTOR (dp, c)))