From: Greg Troxel <gdt@ir.bbn.com>
Subject: Re: inum/double = on 64-bits
Date: 06 Jan 2005 10:06:11 -0500 [thread overview]
Message-ID: <rmiekgysil8.fsf@fnord.ir.bbn.com> (raw)
In-Reply-To: <87brc3mmcl.fsf@zip.com.au>
On a debian alpha, a comparison like
(= #x111111111111111 (exact->inexact #x111111111111110))
gives #t, where on a 32-bit system it's #f.
Is the language clear on what the right answer is? Are you saying
that the behavior is suboptimal, or a violation of R5RS?
On my system, I get #t. A perhaps related suboptimality is in
printing large inexact values.
On NetBSD/i386 2.0ish, guile 1.6.5:
guile> (= #x111111111111111 (exact->inexact #x111111111111110))
#t
guile> #x111111111111110
76861433640456464
guile> (exact->inexact #x111111111111110)
76861433640456500.0
guile> (inexact->exact (exact->inexact #x111111111111110))
76861433640456464
NetBSD/sparc64 (LP64) 2.0ish, guile 1.6.4:
guile> (= #x111111111111111 (exact->inexact #x111111111111110))
#t
guile> #x111111111111110
76861433640456464
guile> (exact->inexact #x111111111111110)
76861433640456500.0
guile> (inexact->exact (exact->inexact #x111111111111110))
76861433640456464
It seems odd to me (from a user viewpoint, but also from thinking
about the implementation) that inexact->exact can restore information
that had appeared missing.
I wonder if I am seeing the effects of the extra floating point bits
beyond IEEE754 on i386, but I see the same behavior on sparc64.
--
Greg Troxel <gdt@ir.bbn.com>
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next prev parent reply other threads:[~2005-01-06 15:06 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-06 0:29 inum/double = on 64-bits Kevin Ryde
2005-01-06 15:06 ` Greg Troxel [this message]
2005-01-06 23:15 ` Kevin Ryde
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