From: Rob Browning <rlb@defaultvalue.org>
Cc: guile-devel@gnu.org
Subject: Re: GMP code committed -- watch for bugs.
Date: Sun, 06 Apr 2003 13:43:40 -0500 [thread overview]
Message-ID: <87vfxrv543.fsf@raven.i.defaultvalue.org> (raw)
In-Reply-To: <xy7of3kkmtf.fsf@nada.kth.se> (Mikael Djurfeldt's message of "Sun, 06 Apr 2003 11:16:44 +0200")
Mikael Djurfeldt <djurfeldt@nada.kth.se> writes:
> numbits = mpz_sizeinbase (SCM_I_BIG_MPZ (num), 2);
> if (UNSIGNED) numbits++;
> scm_remember_upto_here_1 (num);
> if (numbits > (sizeof (ITYPE) * 8))
> scm_out_of_range (s_caller, num);
>
> Firstly, you probably intended to write "if (!UNSIGNED)" (to make room
> for the sign bit).
Indeed.
> Secondly, that doesn't work either. For example, the absolute value
> of LLONG_MIN requires 64 bits, even though it is a signed number.
> So, regardless if we have "if (UNSIGNED)" or "if (!UNSIGNED)" there
> will always be a case where a valid long_long or ulong_long will
> cause an out_of_range error.
Hmm. Actually it looks like mpz_sizeinbase includes the needed sign
bit in its computation (for some reason I thought it didn't). So I
don't think we need the numbits++ at all.
--
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG starting 2002-11-03 = 14DD 432F AE39 534D B592 F9A0 25C8 D377 8C7E 73A4
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next prev parent reply other threads:[~2003-04-06 18:43 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-04 22:34 GMP code committed -- watch for bugs Rob Browning
2003-04-05 12:24 ` Marius Vollmer
2003-04-05 21:51 ` Mikael Djurfeldt
2003-04-05 22:26 ` Rob Browning
2003-04-06 7:41 ` Mikael Djurfeldt
2003-04-06 9:16 ` Mikael Djurfeldt
2003-04-06 18:43 ` Rob Browning [this message]
2003-04-06 19:12 ` Mikael Djurfeldt
2003-04-06 20:09 ` Rob Browning
2003-04-06 20:25 ` Rob Browning
2003-04-06 9:23 ` Mikael Djurfeldt
2003-04-06 20:15 ` Rob Browning
2003-04-06 22:50 ` Kevin Ryde
2003-05-10 0:22 ` GMP code committed -- watch for bugs ... gcd n 0 Kevin Ryde
2003-04-23 22:40 ` GMP code committed -- watch for bugs Kevin Ryde
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