Re: capslock changes control characters?

[Kenichi Handa <handa@m17n.org>]

In article <E1JTPMO-0000WA-5C@fencepost.gnu.org>, Richard Stallman <rms@gnu.org> writes:

> [I sent this message a week ago but did not get a response.]
> Would someone please DTRT and ack?
[...]
> From: "Chris Moore" <christopher.ian.moore@gmail.com>
> To: emacs-pretest-bug@gnu.org
> Subject: capslock changes control characters?

> I tried to insert a TAB into a C++ mode buffer by typing:

>   C-q C-i

> I got an error:

> Debugger entered--Lisp error: (wrong-type-argument char-or-string-p 33554441)

I've just installed a fix.  It required changes to several
places, and among them I'm not sure the following changes
are ok.

2008-03-05  Kenichi Handa  <handa@ni.aist.go.jp>

	* lread.c (Fread_char): Resolve modifiers.
	(Fread_char_exclusive): Likewise.

Previously (read-char) returned 33554441 when you type C-I
(i.e. C-S-i).  I changed it to return 9 (i.e. C-i).  It is
also changed to return 233 upon M-i instead of 134217833.
They still return a code containing unresolvable modifiers.

The algorithm of resolving modifiers is implemented in
char_resolve_modifier_mask as below:

int
char_resolve_modifier_mask (c)
     int c;
{
  /* A non-ASCII character can't reflect modifier bits to the code.  */
  if (! ASCII_CHAR_P ((c & ~CHAR_MODIFIER_MASK)))
    return c;

  /* For Meta, Shift, and Control modifiers, we need special care.  */
  if (c & CHAR_SHIFT)
    {
      /* Shift modifier is valid only with [A-Za-z].  */
      if ((c & 0377) >= 'A' && (c & 0377) <= 'Z')
	c &= ~CHAR_SHIFT;
      else if ((c & 0377) >= 'a' && (c & 0377) <= 'z')
	c = (c & ~CHAR_SHIFT) - ('a' - 'A');
      /* Shift modifier for control characters and SPC is ignored.  */
      else if ((c & ~CHAR_MODIFIER_MASK) <= 0x20)
	c &= ~CHAR_SHIFT;
    }
  if (c & CHAR_CTL)
    {
      /* Simulate the code in lread.c.  */
      /* Allow `\C- ' and `\C-?'.  */
      if ((c & 0377) == ' ')
	c &= ~0177 & ~ CHAR_CTL;
      else if ((c & 0377) == '?')
	c = 0177 | (c & ~0177 & ~CHAR_CTL);
      /* ASCII control chars are made from letters (both cases),
	 as well as the non-letters within 0100...0137.  */
      else if ((c & 0137) >= 0101 && (c & 0137) <= 0132)
	c &= (037 | (~0177 & ~CHAR_CTL));
      else if ((c & 0177) >= 0100 && (c & 0177) <= 0137)
	c &= (037 | (~0177 & ~CHAR_CTL));
    }
  if (c & CHAR_META)
    {
      /* Move the meta bit to the right place for a string.  */
      c = (c & ~CHAR_META) | 0x80;
    }

  return c;
}

---
Kenichi Handa
handa@ni.aist.go.jp