Re: strtold does not set errno when it should

Corinna Vinschen <[email protected]> Mon, 16 Dec 2019 10:11:04 +0100

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

Hi Bruno,

[moving this discussion to the newlib list since that's newlib code]

On Dec 12 07:38, Bruno Haible wrote:
> POSIX [1] makes it clear that when the value to be returned would cause
> underflow, it should set errno to ERANGE.
> 
> [1] <https://pubs.opengroup.org/onlinepubs/9699919799/functions/strtod.html>
> 
> This test case fails with error code 4 on Cygwin 2.9.
> 
> ========================== foo.c ==========================
> #include <stdlib.h>
> #include <errno.h>
> #include <float.h>
> #include <math.h>
> 
> int main ()
> {
>   const char input[] = "1E-100000";
>   char *ptr;
>   long double result;
>   errno = 0;
>   result = strtold (input, &ptr);
>   if (!(ptr == input + 9))
>     return 1;
>   if (!(0.0L <= result && result <= LDBL_MIN))
>     return 2;
>   if (signbit (result))
>     return 3;
>   if (result == 0.0L && errno != ERANGE)
>     return 4;
>   return 0;
> }
> ============================================================
> $ gcc -Wall foo.c
> $ ./a.exe
> $ echo $?
> 4
> 
> The corresponding test case for strtod() / 'double' succeeds.

The code for strtold is almost verbatim taken from

  https://github.com/jwiegley/gdtoa.git

There haven't been any patches upstream.  I, for one, am not overly
fluent with FP math, so I'm glad for any help.

Looking into _strtodg_l (newlib/libc/stdlib/strtodg.c) I tried this
patch:

diff --git a/newlib/libc/stdlib/strtodg.c b/newlib/libc/stdlib/strtodg.c
index 013315946c1b..d6fb26ad3b45 100644
--- a/newlib/libc/stdlib/strtodg.c
+++ b/newlib/libc/stdlib/strtodg.c
@@ -1091,6 +1091,10 @@ _strtodg_l (struct _reent *p, const char *s00, char **se, FPI *fpi, Long *exp,
 				irv |= STRTOG_Underflow;
 			}
 		}
+#ifndef NO_ERRNO
+	if (irv & STRTOG_Underflow)
+		errno = ERANGE;
+#endif
 	if (se)
 		*se = (char *)s;
 	if (sign)

which seems to do the trick.  But, does it make sense?  If not, I'd
really appreciate a patch.


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer

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