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Date: Mon, 19 Apr 2021 22:12:23 +0200
To: cygwin AT cygwin DOT com
Subject: Re: should scanf be getting built supporting hexadecimal float
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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Cc: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
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On Apr 19 19:53, Corinna Vinschen via Cygwin wrote:
> On Apr 19 09:17, Brian Inglis wrote:
> > On 2021-04-19 09:07, Brian Inglis wrote:
> > > On 2021-04-18 22:09, Keith Thompson via Cygwin wrote:
> > > > The *scanf() functions don't handle hexadecimal floating-point input
> > > > (for example "0x1p+0" representing 1.0).
> > > > On Cygwin, the output (compiled with gcc or clang) is:
> > > > sscanf returned 1, x = 0 (expected 1), FAILED
> > > > On Ubuntu, the output is:
> > > > sscanf returned 1, x = 1, PASSED
> > > > Looking through the newlib sources (git://sourceware.org/git/newlib-cygwin.git),
> > > > this might be related to the _WANT_IO_C99_FORMATS macro, but I haven't
> > > > looked into
> > > > the details.
> > > > The test case passes on Cygwin when compiled with i686-w64-mingw32-gcc
> > > > or x86_64-w64-mingw32-gcc.
> > 
> > > This seems like an oversight as gdtoa-gethex.c was added about 2006 and
> > > scanf and strtod support it.
> > > See augmented STC with strtod added attached:
> > > 
> > > $ gcc -o hexfloat-scanf-test{,.c}
> > > $ ./hexfloat-scanf-test
> > > sscanf returned 2, unscanned 'x1p+0', x = 0 (expected 1), FAILED
> > > strtod unscanned '', x = 1, PASSED
> > 
> > Should the Cygwin newlib build be enabling hex float support?
> 
> Unfortunately, newlib's scanf code does not support hex floats at all yet.
> Scanf collects and validates the input stream snippet which is supposed to
> be given to strtod/strtold, and neither x nor p are valid chars in that
> piece of code yet.
> 
> I'll look into adding this code, which shouldn't be too complicated,
> but I wouldn't be offended by patches either.

I pushed a patch which hopefully does the trick

https://sourceware.org/git/?p=newlib-cygwin.git;a=commitdiff;h=9c6c2fb0f697

I also uploaded new developer snapshots to https://cygwin.com/snapshots/

Please give it a try.


Thanks,
Corinna
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