diff options
Diffstat (limited to 'lib/signbitf.c')
-rw-r--r-- | lib/signbitf.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/lib/signbitf.c b/lib/signbitf.c index c172b5fbef..d7e0663c7b 100644 --- a/lib/signbitf.c +++ b/lib/signbitf.c @@ -30,11 +30,19 @@ int gl_signbitf (float arg) { #if defined FLT_SIGNBIT_WORD && defined FLT_SIGNBIT_BIT + /* The use of a union to extract the bits of the representation of a + 'long double' is safe in practice, despite of the "aliasing rules" of + C99, because the GCC docs say + "Even with '-fstrict-aliasing', type-punning is allowed, provided the + memory is accessed through the union type." + and similarly for other compilers. */ # define NWORDS \ ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) union { float value; unsigned int word[NWORDS]; } m; m.value = arg; return (m.word[FLT_SIGNBIT_WORD] >> FLT_SIGNBIT_BIT) & 1; +#elif HAVE_COPYSIGNF_IN_LIBC + return copysignf (1.0f, arg) < 0; #else /* This does not do the right thing for NaN, but this is irrelevant for most use cases. */ |