Re: [PATCH] bypass broken inline strtod() definition in <stdlib.h> on Mingw

[Eric Blake]

[adding bug-autoconf]

On 06/13/2010 05:43 PM, Bruno Haible wrote:
> Hi Ben,
> 
>> The problem is that AC_FUNC_STRTOD assumes that strtod does not
>> exist when cross-compiling, which in turn makes the strtod module
>> assume that it does not need to handle an existing declaration.
> 
> Ah, so AC_FUNC_STRTOD makes gnulib think that strtod() does not exist,
> although in fact it does exist. Just because of the worst-case guess
> that says "ac_cv_func_strtod=no".
> 
>   - When we are cross-compiling, we should avoid pessimistic guesses
>     such as "ac_cv_func_strtod=no". The reason is that the most frequent
>     use of cross-compiling is done for embedded Linux devices (devices
>     with BusyBox, or everything-on-a-chip systems). In such cases,
>     it is not well seen if gnulib provides a replacement function when
>     in fact it is not needed at all. So, please, when cross-compiling,
>     give a thought to the embedded Linux case (with glibc or uClibc).
> 
>     So: Do current embedded Linuxes have the strtod bugs or not? Take a
>     look at the AC_FUNC_STRTOD macro in autoconf/lib/autoconf/functions.m4:
> 
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1537)# 
> AC_FUNC_STRTOD
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1538)# 
> --------------
> 7134f17d        (Akim Demaille  2002-09-28 14:06:07 +0000       
> 1539)AN_FUNCTION([strtod], [AC_FUNC_STRTOD])
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       
> 1540)AC_DEFUN([AC_FUNC_STRTOD],
> 1492d7c5        (Akim Demaille  2001-11-12 15:47:35 +0000       
> 1541)[AC_SUBST(POW_LIB)dnl
> 1492d7c5        (Akim Demaille  2001-11-12 15:47:35 +0000       
> 1542)AC_CACHE_CHECK(for working strtod, ac_cv_func_strtod,
> 6a2a74c2        (Akim Demaille  2001-07-04 14:37:52 +0000       
> 1543)[AC_RUN_IFELSE([AC_LANG_SOURCE([[
> 11ee0ab5        (Paul Eggert    2004-05-03 20:15:44 +0000       
> 1544)]AC_INCLUDES_DEFAULT[
> 11ee0ab5        (Paul Eggert    2004-05-03 20:15:44 +0000       1545)#ifndef 
> strtod
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1546)double 
> strtod ();
> 11ee0ab5        (Paul Eggert    2004-05-03 20:15:44 +0000       1547)#endif
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1548)int
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1549)main()
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1550){
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1551)  {
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1552)    /* 
> Some versions of Linux strtod mis-parse strings with leading '+'.  */
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1553)    char 
> *string = " +69";
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1554)    char 
> *term;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1555)    
> double value;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1556)    
> value = strtod (string, &term);
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1557)    if 
> (value != 69 || term != (string + 4))
> a71c24a7        (Paul Eggert    2006-04-03 03:18:39 +0000       1558)      
> return 1;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1559)  }
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1560)
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1561)  {
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1562)    /* 
> Under Solaris 2.4, strtod returns the wrong value for the
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1563)       
> terminating character under some conditions.  */
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1564)    char 
> *string = "NaN";
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1565)    char 
> *term;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1566)    
> strtod (string, &term);
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1567)    if 
> (term != string && *(term - 1) == 0)
> a71c24a7        (Paul Eggert    2006-04-03 03:18:39 +0000       1568)      
> return 1;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1569)  }
> a71c24a7        (Paul Eggert    2006-04-03 03:18:39 +0000       1570)  return 
> 0;
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1571)}
> 6a2a74c2        (Akim Demaille  2001-07-04 14:37:52 +0000       1572)]])],
> b44e483c        (Akim Demaille  2003-05-17 10:30:07 +0000       1573)         
>  ac_cv_func_strtod=yes,
> b44e483c        (Akim Demaille  2003-05-17 10:30:07 +0000       1574)         
>  ac_cv_func_strtod=no,
> b44e483c        (Akim Demaille  2003-05-17 10:30:07 +0000       1575)         
>  ac_cv_func_strtod=no)])
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1576)if test 
> $ac_cv_func_strtod = no; then
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1577)  
> _AC_LIBOBJ_STRTOD
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1578)fi
> 7bd04c77        (Akim Demaille  2000-08-01 11:16:33 +0000       1579)])
> 
>     With two old old old tests and no reasonable cross-compiling behaviour I
>     would say that the best thing to do is to move these two blocks of C code
>     into gl_FUNC_STRTOD's test, and stop using AC_FUNC_STRTOD. Then the
>     autoconf documentation can mark this macro obsolescent, and on the gnulib
>     side this test runs one program, not two, and we have full control over
>     the cross-compilation behaviour.

Or even better, why not push those two tests upstream into autoconf,
then have gnulib override AC_FUNC_STRTOD if it detects older autoconf,
so that everyone using upstream AC_FUNC_STRTOD can reliably detect these
same bugs?

> @@ -28,6 +34,24 @@
>  }
>  ]], [[
>    {
> +    /* In some old versions of Linux (2000 or before), strtod mis-parses
> +       strings with leading '+'.  */
> +    const char *string = " +69";
> +    char *term;
> +    double value = strtod (string, &term);
> +    if (value != 69 || term != (string + 4))
> +      return 1;
> +  }
> +  {
> +    /* Under Solaris 2.4, strtod returns the wrong value for the
> +       terminating character under some conditions.  */
> +    const char *string = "NaN";
> +    char *term;
> +    strtod (string, &term);
> +    if (term != string && *(term - 1) == 0)
> +      return 1;
> +  }
> +  {
>      /* Older glibc and Cygwin mis-parse "-0x".  */
>      const char *string = "-0x";
>      char *term;
> 
> 
> 

-- 
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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