mirror/autoconf
2
0
Fork 0
mirror of git://git.sv.gnu.org/autoconf synced 2025-03-13 14:36:50 +08:00
Code Issues Packages Projects Releases Wiki Activity

(Function Portability): Document isinf and

Browse Source 
and isnan.  From a suggestion by Kevin Ryde.
This commit is contained in:
Paul Eggert 2004-08-12 21:51:48 +00:00
parent 7a8ea3e87f
commit 70d0937ae4
1 changed files with 52 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
doc/autoconf.texi
View File

@ -3670,6 +3670,58 @@ tradition of it returning @code{int}.
The ISO C99 standard says a call @code{free(NULL)} does nothing, but
some old systems don't support this (eg.@: NextStep).
@item @code{isinf}
@itemx @code{isnan}
@c @fuindex isinf
@c @fuindex isnan
@prindex @code{isinf}
@prindex @code{isnan}
The ISO C99 standard specifies that @code{isinf} and @code{isnan} are
macros. On some systems just macros are available (e.g., HP-UX), on
some systems both macros and functions (e.g., glibc 2.3.2), and on some
systems only functions (e.g., IRIX 6 and Solaris 9). In some cases
these functions are declared in nonstandard headers like
@code{<sunmath.h>} and defined in non-default libraries like
@option{-lm} or @option{-lsunmath}.
The C99 @code{isinf} and @code{isnan} macros work correctly with
@code{long double} arguments, but pre-C99 systems that use functions
typically assume @code{double} arguments. On such a system,
@code{isinf} incorrectly returns true for a finite @code{long double}
argument that is outside the range of @code{double}.
To work around this porting mess, you can use code like the following.
@example
#include <math.h>
#ifndef isnan
# define isnan(x) \
(sizeof (x) == sizeof (long double) ? isnan_ld (x) \
: sizeof (x) == sizeof (double) ? isnan_d (x) \
: isnan_f (x))
static inline int isnan_f (float x) @{ return x != x; @}
static inline int isnan_d (double x) @{ return x != x; @}
static inline int isnan_ld (long double x) @{ return x != x; @}
#endif
#ifndef isinf
# define isinf(x) \
(sizeof (x) == sizeof (long double) ? isinf_ld (x) \
: sizeof (x) == sizeof (double) ? isinf_d (x) \
: isinf_f (x))
static inline int isinf_f (float x) @{ return isnan (x - x); @}
static inline int isinf_d (double x) @{ return isnan (x - x); @}
static inline int isinf_ld (long double x) @{ return isnan (x - x); @}
#endif
@end example
Use @code{AC_C_INLINE} (@pxref{C Compiler}) so that this code works on
compilers that lack the @code{inline} keyword. Some optimizing
compilers mishandle these definitions, but systems with that bug
typically have missing or broken @code{isnan} functions anyway, so it's
probably not worth worrying about.
@item @code{malloc}
@c @fuindex malloc
@prindex @code{malloc}