modules.h
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1 /*
2  * Copyright (C) 2014 Freie Universit├Ąt Berlin
3  * 2017 HAW-Hamburg
4  *
5  * This file is subject to the terms and conditions of the GNU Lesser
6  * General Public License v2.1. See the file LICENSE in the top level
7  * directory for more details.
8  */
9 
21 #ifndef MODULES_H
22 #define MODULES_H
23 
24 #ifdef __cplusplus
25 extern "C" {
26 #endif
27 
60 #define IS_ACTIVE(macro) __is_active(macro)
61 
71 #define IS_USED(module) IS_ACTIVE(module)
72 
76 /* Here a prefix "__PREFIX_WHEN_" is added to the macro. So if it was a 1 we
77  * have "__PREFIX_WHEN_1", and if it was not defined we have "__PREFIX_WHEN_".
78  */
79 #define __is_active(val) ___is_active(__PREFIX_WHEN_##val)
80 
81 /* With this placeholder we turn the original value into two arguments when the
82  * original value was defined as 1 (note the comma).
83  */
84 #define __PREFIX_WHEN_1 0,
85 
86 /* Here we add two extra arguments, that way the next macro can accept varargs.
87  *
88  * If the original macro was defined as 1, this will have three arguments
89  * (__take_second_arg(0, 1, 0, 0)), otherwise it will have two
90  * (__take_second_arg(__PREFIX_WHEN_ 1, 0, 0)). The third zero is there just to
91  * be compliant with C99, which states that when a function-like macro ends
92  * with ellipsis (...) it should be called with at least one argument for the
93  * variable list.
94  */
95 #define ___is_active(arg1_or_junk) __take_second_arg(arg1_or_junk 1, 0, 0)
96 
97 /* Finally, we just always take the second argument, which will be either 1
98  * (when three arguments are passed, i.e. macro was defined as 1) or 0 (when
99  * only two arguments are passed).
100  */
101 #define __take_second_arg(__ignored, val, ...) val
106 #ifdef __cplusplus
107 }
108 #endif
109 
110 #endif /* MODULES_H */