RFC: Fix partial NaN-parsing problem [was RE: sscanf problem]

[Jean-Christophe Kablitz]

Hello,

I have noticed, that, while parsing {a float_value immediately followed by 
'n' or 'N'} with the "%f%c" format, the sscanf function of cygwin-1.5.16-1 
behaves differently from the scanf function of cygwin-1.5.14-1.
Until cygwin-1.5.14-1 (included), 'n' matches %c, while with cygwin-1.5.15-1 
and cygwin-1.5-16-1, 'n' is no more assigned to %c.

In the following test case, I would expect the progran to output
i=2 x=1 m=a
i=2 x=1 m=n

that was the case until cygwin-1.5.14-1 (included).

With cygwin-1.5.15-1 and cygwin-1.5-16-1, the program outputs instead
i=2 x=1 m=a
i=1 x=1 m=_

Maybe I have been misusing sscanf. Or there is a relationship with the 
NaN-parsing problem of the "newlib".

Best regards.
Jean-Christophe K.

--- beginning of test case ---
jck:/sscanf> cat ssn.c
#include <stdio.h>

int main()
{
    double x;
    char   m;
    int    i;

    x = 0.0;
    m = '_';
    i = sscanf("1.0a", "%lf%c", &x, &m);
    printf("i=%d x=%g m=%c\n", i, x, m);
    x = 0.0;
    m = '_';
    i = sscanf("1.0n", "%lf%c", &x, &m);
    printf("i=%d x=%g m=%c\n", i, x, m);
    return 0;
}

jck:/sscanf> gcc -O0 ssn.c -o ssn.exe
jck:/sscanf> ./ssn.exe
i=2 x=1 m=a
i=1 x=1 m=_
--- end of test case ---

----- Original Message ----- 
From: "Jeff Johnston" <jjohnstn at redhat dot com>
To: "Dave Korn" <dave dot korn at artimi dot com>
Cc: <cygwin at cygwin dot com>; <newlib at sources dot redhat dot com>
Sent: Tuesday, April 05, 2005 8:47 PM
Subject: Re: RFC: Fix partial NaN-parsing problem [was RE: sscanf problem]


> Patch checked in.  Thanks.
>
> -- Jeff J.
>
> Dave Korn wrote:
>> ----Original Message----
>>
>>>From: Dave Korn
>>>Sent: 04 April 2005 19:07
>>
>>
>>>----Original Message----
>>>
>>>>From: Dave Korn
>>>>Sent: 04 April 2005 18:51
>>>
>>>>----Original Message----
>>>>
>>>>>From: Michael Hines
>>>>>Sent: 04 April 2005 19:43
>>>>
>>>>>The following program prints
>>>>>i=1 x=0
>>>>>instead of
>>>>>i=0 x=10
>>>>>when using the latest version of cygwin1.dll.
>>
>>
>>>  No, hang on, on checking the newlib-l archive that seems to have been
>>>something to do with a zero exponent.  This is a separate bug: it accepts
>>>the first one or two characters of 'nan' and says "ok, everything's still
>>>good", and then because it's reached the end of the string it treats that
>>>as a successful parse; it forgets to verify that it doesn't have an
>>>outstanding half-formed NaN.  I'll post a (provisional) patch shortly.
>>
>>
>>   Ok, this is only provisional, because as I point out I'm not quite sure
>> about the corner case where we've refilled the buffer.  It also has minor
>> formatting issues (slightly long lines in the comment, IMO).  However, it
>> fixes the testcase, and I've got to go home for the evening, so here's my
>> work-in-progress; comments welcomed.
>>
>> ---------------------------<snip!>---------------------------
>> dk@mace /test/sscanf> cat ss.c
>>
>> #include <stdio.h>
>> int main() {
>>          int i;
>>          double x;
>>          x = 10;
>>          i = sscanf("n", "%lf", &x);
>>          printf("i=%d x=%g\n", i, x);
>>          i = sscanf("nan", "%lf", &x);
>>          printf("i=%d x=%g\n", i, x);
>>          return 0;
>> }
>>
>>
>>
>> dk@mace /test/sscanf> gcc -O0 -g ss.c -o ss.exe
>> dk@mace /test/sscanf> ./ss.exe
>> i=0 x=10
>> i=1 x=NaN
>> dk@mace /test/sscanf>
>> ---------------------------<snip!>---------------------------
>>
>>
>>
>>
>>
>>     cheers,
>>       DaveK
>
>
> --
> Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
> Problem reports:       http://cygwin.com/problems.html
> Documentation:         http://cygwin.com/docs.html
> FAQ:                   http://cygwin.com/faq/
> 


--
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
Problem reports:       http://cygwin.com/problems.html
Documentation:         http://cygwin.com/docs.html
FAQ:                   http://cygwin.com/faq/