diff mbox

Don't treat rint as setting errno

Message ID 87egg3tbm5.fsf@e105548-lin.cambridge.arm.com
State New
Headers show

Commit Message

Richard Sandiford Nov. 6, 2015, 3:02 p.m. UTC 
builtins.def says that rint sets errno, but it looks like this might
be a mistake.  C99 says that rint doesn't set errno and the builtins.c
expansion code doesn't try to keep errno up to date.

Perhaps this was because earlier versions of POSIX said that
rint sets errno on overflow:

    http://pubs.opengroup.org/onlinepubs/009695399/functions/rintf.html

However, this is another instance of the observation that "rounding
functions could never overflow" (because anything using exponents
that large is already integral).  The page above also says that
differences with C99 are unintentional and the ERANGE clause has
been removed from later versions of POSIX:

    http://pubs.opengroup.org/onlinepubs/9699919799/functions/rint.html

Also, the version of POSIX that lists ERANGE for rint does the same
for nearbyint:

    http://pubs.opengroup.org/onlinepubs/009695399/functions/nearbyintf.html

and we already treat nearbyint as not setting errno.  This too has been
clarified in later versions of POSIX:

    http://pubs.opengroup.org/onlinepubs/9699919799/functions/nearbyint.html

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.
OK to install?

Thanks,
Richard


gcc/
	* builtins.def (BUILTIN_RINT, BUILTIN_RINTF, BUILTIN_RINTL): Use
	ATTR_MATHFN_FPROUNDING rather than ATTR_MATHFN_FPROUNDING_ERRNO.

Comments

Bernd Schmidt Nov. 6, 2015, 3:17 p.m. UTC | #1 
On 11/06/2015 04:02 PM, Richard Sandiford wrote:
> builtins.def says that rint sets errno, but it looks like this might
> be a mistake.  C99 says that rint doesn't set errno and the builtins.c
> expansion code doesn't try to keep errno up to date.

[snip explanation of the history]

FWIW the manpage has this to say:

"SUSv2 and POSIX.1-2001 contain text about overflow (which might set 
errno to ERANGE, or raise an FE_OVERFLOW exception).  In practice, the 
result cannot overflow on any current machine, so this error-handling 
stuff is just  nonsense."

> Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.
> OK to install?

Ok.


Bernd
diff mbox

Patch

diff --git a/gcc/builtins.def b/gcc/builtins.def
index 886b45c..076da40 100644
--- a/gcc/builtins.def
+++ b/gcc/builtins.def
@@ -475,9 +475,9 @@  DEF_C99_BUILTIN        (BUILT_IN_REMAINDERL, "remainderl", BT_FN_LONGDOUBLE_LONG
 DEF_C99_BUILTIN        (BUILT_IN_REMQUO, "remquo", BT_FN_DOUBLE_DOUBLE_DOUBLE_INTPTR, ATTR_MATHFN_FPROUNDING_STORE)
 DEF_C99_BUILTIN        (BUILT_IN_REMQUOF, "remquof", BT_FN_FLOAT_FLOAT_FLOAT_INTPTR, ATTR_MATHFN_FPROUNDING_STORE)
 DEF_C99_BUILTIN        (BUILT_IN_REMQUOL, "remquol", BT_FN_LONGDOUBLE_LONGDOUBLE_LONGDOUBLE_INTPTR, ATTR_MATHFN_FPROUNDING_STORE)
-DEF_C99_BUILTIN        (BUILT_IN_RINT, "rint", BT_FN_DOUBLE_DOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
-DEF_C99_BUILTIN        (BUILT_IN_RINTF, "rintf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING_ERRNO)
-DEF_C99_BUILTIN        (BUILT_IN_RINTL, "rintl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_MATHFN_FPROUNDING_ERRNO)
+DEF_C99_BUILTIN        (BUILT_IN_RINT, "rint", BT_FN_DOUBLE_DOUBLE, ATTR_MATHFN_FPROUNDING)
+DEF_C99_BUILTIN        (BUILT_IN_RINTF, "rintf", BT_FN_FLOAT_FLOAT, ATTR_MATHFN_FPROUNDING)
+DEF_C99_BUILTIN        (BUILT_IN_RINTL, "rintl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_MATHFN_FPROUNDING)
 DEF_C99_BUILTIN        (BUILT_IN_ROUND, "round", BT_FN_DOUBLE_DOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDF, "roundf", BT_FN_FLOAT_FLOAT, ATTR_CONST_NOTHROW_LEAF_LIST)
 DEF_C99_BUILTIN        (BUILT_IN_ROUNDL, "roundl", BT_FN_LONGDOUBLE_LONGDOUBLE, ATTR_CONST_NOTHROW_LEAF_LIST)