From: Hongyi Zhao <hongyi.zhao@gmail.com>
To: Omar Polo <op@omarpolo.com>
Cc: help-gnu-emacs <help-gnu-emacs@gnu.org>
Subject: Re: The correspondence of the command-name and its key-sequence.
Date: Mon, 11 Jan 2021 16:04:19 +0800 [thread overview]
Message-ID: <CAGP6POKpYD5zccXu07yPQwazYHj10U37c2YLeWK+TVQp1FYsXw@mail.gmail.com> (raw)
In-Reply-To: <87h7nqe8gb.fsf@omarpolo.com>
On Sat, Jan 9, 2021 at 6:00 PM Omar Polo <op@omarpolo.com> wrote:
>
>
> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>
> > On Sat, Jan 9, 2021 at 4:23 PM Omar Polo <op@omarpolo.com> wrote:
> >[..]
> >>
> >> You shouldn't mix the hexadecimal and decimal representation of the
> >> characters. The ASCII characters 0x01-0x1a (inclusive), i.e. the
> >> characters in the range 1-26 (decimal), are the ctrl- variant of the A-Z
> >> ASCII characters (0x41-0x5a).
> >
> > Why is the ASCII table designed into this strange layout?
>
> I have no clue. I wasn't there when they designed it :)
>
> >> I don't remember if the following is right, so please correct me if I'm
> >> wrong, but the keyboards (the old ones I mean) when pressing the ctrl-
> >> key along with a letter would apply a bitmask on that key. If you look
> >> at this wikipedia page[0], you'll see that the ASCII character 0x01
> >> "Start of Heading" is mapped to C-a. Now, if you look at the byte
> >> representation of the 'A' character in ASCII it is
> >>
> >> 4 1 (decimal)
> >> 0010 0001 (hexadecimal)
> >>
> >> and that SOH is
> >>
> >> 0 1 (decimal)
> >> 0000 0001 (hexadecimal)
> >>
> >>
> >> and so on, B is mapped to to STX, C to ETX, ... G to the BELL character,
> >> ... I to the hard tab.
> >
> > The `man acsii' says the following:
> >
> > HT '\t' (horizontal tab)
> >
> > Why you describe it as the hard tab?
>
> A Freudian slip. I intended to write horizontal tab :)
>
>
> >> So it seems that CTRL(key) is (key & 0xDF).
> >
> > I still don’t quite understand how this is derived.
>
> it clears the 3rd bit (counting from left to right). For instance, for
> I <-> tab you get
>
> 4 9 (decimal)
> 0010 1001 (binary)
>
> which becomes
>
> 0 9 (decimal)
> 0000 1001 (binary)
> ^
> this one
>
> As you can see, that bit get cleared. 0xDF is 1101 1111, so it should
> "select" every bit but that one.
>
> Note that this works even after the Z. [ (that's right after the Z)
> gets mapped to C-[, which is ESC. \ gets mapped to "field separator" etc
Why the \ has two forms in the ascii document as shown below:
$ man ascii | grep -F '\\'
034 28 1C FS (file separator) 134 92 5C \ '\\'
As you can see, the document gives two forms of it:
\ '\\'
>
> ( [ is 0011 1010, ESC is 0001 1010 )
>
> >> (Again, correct me if I'm
> >> wrong. I recall reading something like this time ago, but I couldn't
> >> find the source now)
> >>
> >> Now, exactly why C-g was chosen for to the keyboard-quit, is something I
> >> don't know, but the fact that by default it produces a BELL character
> >> (on ttys at least) may be a hint.
> >>
> >> [0]:https://en.wikipedia.org/wiki/C0_and_C1_control_codes#Basic_ASCII_control_codes
> >
> > Thanks a lot for this interesting and presumably feasible analysis.
> >
> > Best,
>
--
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Polytechnic University of Science and Technology engineering
NO. 552 North Gangtie Road, Xingtai, China
next prev parent reply other threads:[~2021-01-11 8:04 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-09 6:05 The correspondence of the command-name and its key-sequence Hongyi Zhao
2021-01-09 6:32 ` Drew Adams
2021-01-09 7:16 ` Hongyi Zhao
2021-01-09 8:23 ` Omar Polo
2021-01-09 9:33 ` Hongyi Zhao
2021-01-09 10:00 ` Omar Polo
2021-01-11 8:04 ` Hongyi Zhao [this message]
2021-01-11 8:20 ` Omar Polo
2021-01-11 9:51 ` tomas
2021-01-09 17:20 ` Francis Belliveau
2021-01-14 22:21 ` ASCII - Why...? -- as promised Francis Belliveau
2021-01-09 21:21 ` The correspondence of the command-name and its key-sequence Drew Adams
2021-01-09 17:39 ` Kévin Le Gouguec
2021-01-09 18:47 ` Eduardo Ochs
2021-01-09 22:29 ` Kévin Le Gouguec
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAGP6POKpYD5zccXu07yPQwazYHj10U37c2YLeWK+TVQp1FYsXw@mail.gmail.com \
--to=hongyi.zhao@gmail.com \
--cc=help-gnu-emacs@gnu.org \
--cc=op@omarpolo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).