From: Richard Sandiford <rsandifo@redhat.com>
To: binutils@sources.redhat.com
Subject: Re: Bignums and .sleb128
Date: Mon, 31 Jan 2005 21:33:00 -0000 [thread overview]
Message-ID: <87brb5p9mp.fsf@firetop.home> (raw)
In-Reply-To: <20050131195417.GA6254@nevyn.them.org> (Daniel Jacobowitz's message of "Mon, 31 Jan 2005 14:54:17 -0500")
Daniel Jacobowitz <drow@false.org> writes:
> I spent most of this morning chasing a bug in .sleb128 support. After
> I finished running around in circles and discovered that Richard Sandiford
> had fixed it two weeks ago (thanks!) I compared the testcases I'd written
> with the ones that he committed. There were a couple of differences,
> basically related to this comment from bignum.h:
>
> * Bignums are >= 0. *
Ugh, didn't notice that, sorry. But I think that comment fell by the
wayside the moment we tried to handle '-' for O_bigs. After all, the
precision of bignums is completely arbitrary, so if the result of
-bignum is supposed to be unsigned, there's no obvious cut-off
point for the sign extension.
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 ;).
> So generating a sleb128 from one is pretty strange - the sign bit is
> ambiguously handled.
Perhaps, but the problem isn't limited to sleb128. E.g.:
.quad -0xffffffffffff
acts in the same way as ".quad 1", not ".quad 0xffff000000000001".
The direction of recent changes suggests there really is a need
for negative bignums, so IMO we should try to support them.
Richard
next prev parent reply other threads:[~2005-01-31 21:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-31 19:54 Daniel Jacobowitz
2005-01-31 21:33 ` Richard Sandiford [this message]
2005-01-31 21:57 ` Daniel Jacobowitz
2005-01-31 22:18 ` Richard Sandiford
2005-01-31 22:22 ` Daniel Jacobowitz
2005-02-01 0:53 Paul Schlie
2005-02-01 1:09 ` Paul Schlie
2005-02-01 5:04 ` Paul Schlie
2005-02-01 3:29 ` Daniel Jacobowitz
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