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Message-ID: <427225A7.5050208@byu.net>
Date: Fri, 29 Apr 2005 06:16:39 -0600
From: Eric Blake <ebb9 AT byu DOT net>
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To: Dave Korn <dave DOT korn AT artimi DOT com>
CC: "'Jeff Johnston'" <jjohnstn AT redhat DOT com>,
   "'Jean-Christophe Kablitz'" <jckablitz AT infonie DOT fr>, cygwin AT cygwin DOT com,
   newlib AT sources DOT redhat DOT com
Subject: Re: [PATCH] Fix newly exposed bug [was RE: RFC: Fix partial NaN-parsing problem [was RE: sscanf problem]]
References: <SERRANOwr2UAaTzvb5Y0000017b AT SERRANO DOT CAM DOT ARTIMI DOT COM>
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According to Dave Korn on 4/28/2005 12:41 PM:
>   Heh, actually we probably have to talk about that.  The k should IIUIC be
> swallowed by the %lf and the %c should fail; this is the production
> described as NAN(n-char-sequence opt) in the C language spec, strtod
> documentation (that's 7.20.1.3.3 in WG14/N843 draft, I don't have the final
> version).  And we haven't even mentioned the lack of INF support yet :)

Per POSIX,
http://www.opengroup.org/onlinepubs/009695399/functions/sscanf.html,
NAN{n-char-sequence} is implementation defined - sscanf should only accept
n-char-sequences that are also generated by the same implementation's
printf and parsed by strtod.  And since newlib printf does not output any
n-char-sequence versions of NaN, sscanf should not parse them.  IIUC,
n-char-sequence exists to allow implementations the ability to specify
signalling NaNs or exact bit patterns within the NaN.

All this means that I think Jeff is right that
 i = sscanf ("nank", "%lf%c%n", &x, &m, &n)
should succeed on newlib, but you should also remember that it is not
portable and that on non-newlib systems it might fail.

- --
Life is short - so eat dessert first!

Eric Blake             ebb9 AT byu DOT net
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