| 1 | /* signbit() macro: Determine the sign bit of a floating-point number. |
| 2 | Copyright (C) 2007, 2009-2014 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 Lesser 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 Lesser General Public License for more details. |
| 13 | |
| 14 | You should have received a copy of the GNU Lesser 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 "isnanf-nolibm.h" |
| 24 | #include "float+.h" |
| 25 | |
| 26 | #ifdef gl_signbitf_OPTIMIZED_MACRO |
| 27 | # undef gl_signbitf |
| 28 | #endif |
| 29 | |
| 30 | int |
| 31 | gl_signbitf (float arg) |
| 32 | { |
| 33 | #if defined FLT_SIGNBIT_WORD && defined FLT_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 (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int)) |
| 42 | union { float value; unsigned int word[NWORDS]; } m; |
| 43 | m.value = arg; |
| 44 | return (m.word[FLT_SIGNBIT_WORD] >> FLT_SIGNBIT_BIT) & 1; |
| 45 | #elif HAVE_COPYSIGNF_IN_LIBC |
| 46 | return copysignf (1.0f, 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 (isnanf (arg)) |
| 51 | return 0; |
| 52 | if (arg < 0.0f) |
| 53 | return 1; |
| 54 | else if (arg == 0.0f) |
| 55 | { |
| 56 | /* Distinguish 0.0f and -0.0f. */ |
| 57 | static float plus_zero = 0.0f; |
| 58 | float arg_mem = arg; |
| 59 | return (memcmp (&plus_zero, &arg_mem, SIZEOF_FLT) != 0); |
| 60 | } |
| 61 | else |
| 62 | return 0; |
| 63 | #endif |
| 64 | } |