From 386e1c26ac473d6863133ab9cbe3bbda16c15816 Mon Sep 17 00:00:00 2001 From: Romain Naour Date: Mon, 16 Oct 2017 23:21:56 +0200 Subject: 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 Cc: Joseph Myers --- math/math.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'math') 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 -- cgit v1.2.3