diff options
| author | Romain Naour <romain.naour@gmail.com> | 2017-10-16 23:21:56 +0200 |
|---|---|---|
| committer | Gabriel F. T. Gomes <gabriel@inconstante.eti.br> | 2017-10-17 12:06:44 -0200 |
| commit | 386e1c26ac473d6863133ab9cbe3bbda16c15816 (patch) | |
| tree | 7c645ee0d6c11960740cd05edbcd840db4eae6ea /math | |
| parent | 3d265601358974c9be8264e53dadd8f9aea5690c (diff) | |
Let signbit use the builtin in C++ mode with gcc < 6.x (bug 22296)
When using gcc < 6.x, signbit does not use the type-generic
__builtin_signbit builtin, instead it uses __MATH_TG.
However, when library support for float128 is available, __MATH_TG uses
__builtin_types_compatible_p, which is not available in C++ mode.
On the other hand, libstdc++ undefines (in cmath) many macros from
math.h, including signbit, so that it can provide its own functions.
However, during its configure tests, libstdc++ just tests for the
availability of the macros (it does not undefine them, nor does it
provide its own functions).
Finally, libstdc++ configure tests include math.h and get the definition
of signbit that uses __MATH_TG (and __builtin_types_compatible_p).
Since libstdc++ does not undefine the macros during its configure
tests, they fail.
This patch lets signbit use the builtin in C++ mode when gcc < 6.x is
used. This allows the configure test in libstdc++ to work.
Tested for x86_64.
[BZ #22296]
* math/math.h: Let signbit use the builtin in C++ mode with gcc
< 6.x
Cc: Gabriel F. T. Gomes <gftg@linux.vnet.ibm.com>
Cc: Joseph Myers <joseph@codesourcery.com>
Diffstat (limited to 'math')
| -rw-r--r-- | math/math.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/math/math.h b/math/math.h index faa2481731..5ad8156555 100644 --- a/math/math.h +++ b/math/math.h @@ -448,6 +448,15 @@ enum /* Return nonzero value if sign of X is negative. */ # if __GNUC_PREREQ (6,0) # define signbit(x) __builtin_signbit (x) +# elif defined __cplusplus + /* In C++ mode, __MATH_TG cannot be used, because it relies on + __builtin_types_compatible_p, which is a C-only builtin. + The check for __cplusplus allows the use of the builtin instead of + __MATH_TG. This is provided for libstdc++, only to let its configure + test work. No further use of this definition of signbit is expected + in C++ mode, since libstdc++ provides its own version of signbit + in cmath (which undefines signbit). */ +# define signbit(x) __builtin_signbitl (x) # elif __GNUC_PREREQ (4,0) # define signbit(x) __MATH_TG ((x), __builtin_signbit, (x)) # else |