From: Paul Schlie <schlie@comcast.net>
To: Daniel Jacobowitz <drow@false.org>,
Richard Sandiford <rsandifo@redhat.com>
Cc: <binutils@sources.redhat.com>
Subject: Re: Bignums and .sleb128
Date: Tue, 01 Feb 2005 00:53:00 -0000 [thread overview]
Message-ID: <BE243D1B.8DB0%schlie@comcast.net> (raw)
> Daniel Jacobowitz <drow@false.org> writes:
> >> You said later that:
> >>
> >> > If we're going to use these semantics, at least the '-' case in
> >> > operand() needs to be fixed.
> >>
> >> but I wasn't sure what you meant by "these semantics". Do you mean
> >> treating bignums as signed, or treating them as unsigned? By my reading,
> >> operand()'s current handling of '-' already assumes they are signed,
> >> just like the sleb128 code does (and did ;).
> > It doesn't work, because sometimes bignums are signed and sometimes
> > they aren't. Consider -0xffffffffffff; the current code will return 1.
> > If you want to treat the input as unsigned, then you need to add a new
> > word with the sign bit. Note that with one less leading 'f', it
> > suddenly works.
Strongly suspect that the proper idiom to is to treat all non-explicitly
negative constants as being unsigned values; where the point of confusion
is that with the exception of decimal numbers; binary, octal, and hex
digits directly correspond to N-bit patters which were likely specified
as such with the implicit intent they be preserved, the only remaining
ambiguity is whether the most-significant specified set-bit is intended
to be sign-extended if the value is stored with greater precision than
than the otherwise required as determined by the most-significant non-0
bit position i.e.:
-0x1 == [1...]1, where [1...] represents the variable precision
sign-extension of the most significant bit explicitly specified, which
would otherwise only require a signed-bit-field:1, but would need to
be sign extended to fill the remaining most-significant bits if stored
with greater precision as may be required.
Thereby all constant values may be treated uniformly:
+1 == +0b01 == +0x1 ...
-1 == -0b01 == -0x1 ...
+2 == +0b10 == +0x2 ...
-2 == -0b10 == -0x2 ...
Which seems quite sensible.
next reply other threads:[~2005-02-01 0:53 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-02-01 0:53 Paul Schlie [this message]
2005-02-01 1:09 ` Paul Schlie
2005-02-01 5:04 ` Paul Schlie
2005-02-01 3:29 ` Daniel Jacobowitz
-- strict thread matches above, loose matches on Subject: below --
2005-01-31 19:54 Daniel Jacobowitz
2005-01-31 21:33 ` Richard Sandiford
2005-01-31 21:57 ` Daniel Jacobowitz
2005-01-31 22:18 ` Richard Sandiford
2005-01-31 22:22 ` Daniel Jacobowitz
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
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=BE243D1B.8DB0%schlie@comcast.net \
--to=schlie@comcast.net \
--cc=binutils@sources.redhat.com \
--cc=drow@false.org \
--cc=rsandifo@redhat.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).