Commit | Line | Data |
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52414043 | 1 | /* signbit() macro: Determine the sign bit of a floating-point number. |
5e69ceb7 | 2 | Copyright (C) 2007-2014 Free Software Foundation, Inc. |
52414043 MW |
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 "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 | } |