1 /* signbit() macro: Determine the sign bit of a floating-point number. 2 Copyright (C) 2007-2012 Free Software Foundation, Inc. 3 4 This program is free software: you can redistribute it and/or modify 5 it under the terms of the GNU General Public License as published by 6 the Free Software Foundation; either version 3 of the License, or 7 (at your option) any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU General Public License for more details. 13 14 You should have received a copy of the GNU General Public License 15 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 16 17 #include <config.h> 18 19 /* Specification. */ 20 #include <math.h> 21 22 #include <string.h> 23 #include "isnand-nolibm.h" 24 #include "float+.h" 25 26 #ifdef gl_signbitd_OPTIMIZED_MACRO 27 # undef gl_signbitd 28 #endif 29 30 int 31 gl_signbitd (double arg) 32 { 33 #if defined DBL_SIGNBIT_WORD && defined DBL_SIGNBIT_BIT 34 /* The use of a union to extract the bits of the representation of a 35 'long double' is safe in practice, despite of the "aliasing rules" of 36 C99, because the GCC docs say 37 "Even with '-fstrict-aliasing', type-punning is allowed, provided the 38 memory is accessed through the union type." 39 and similarly for other compilers. */ 40 # define NWORDS \ 41 ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) 42 union { double value; unsigned int word[NWORDS]; } m; 43 m.value = arg; 44 return (m.word[DBL_SIGNBIT_WORD] >> DBL_SIGNBIT_BIT) & 1; 45 #elif HAVE_COPYSIGN_IN_LIBC 46 return copysign (1.0, arg) < 0; 47 #else 48 /* This does not do the right thing for NaN, but this is irrelevant for 49 most use cases. */ 50 if (isnand (arg)) 51 return 0; 52 if (arg < 0.0) 53 return 1; 54 else if (arg == 0.0) 55 { 56 /* Distinguish 0.0 and -0.0. */ 57 static double plus_zero = 0.0; 58 double arg_mem = arg; 59 return (memcmp (&plus_zero, &arg_mem, SIZEOF_DBL) != 0); 60 } 61 else 62 return 0; 63 #endif 64 } 65
