modules.h

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/*
 * Copyright (C) 2014 Freie Universität Berlin
 *               2017 HAW-Hamburg
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */
 
#ifndef MODULES_H
#define MODULES_H
 
#ifdef __cplusplus
extern "C" {
#endif
 
#define IS_ACTIVE(macro) __is_active(macro)
 
#define IS_USED(module) IS_ACTIVE(module)
 
/* Here a prefix "__PREFIX_WHEN_" is added to the macro. So if it was a 1 we
 * have "__PREFIX_WHEN_1", and if it was not defined we have "__PREFIX_WHEN_".
 */
#define __is_active(val)              ___is_active(__PREFIX_WHEN_##val)
 
/* With this placeholder we turn the original value into two arguments when the
 * original value was defined as 1 (note the comma).
 */
#define __PREFIX_WHEN_1 0,
 
/* Here we add two extra arguments, that way the next macro can accept varargs.
 *
 * If the original macro was defined as 1, this will have three arguments
 * (__take_second_arg(0, 1, 0, 0)), otherwise it will have two
 * (__take_second_arg(__PREFIX_WHEN_ 1, 0, 0)). The third zero is there just to
 * be compliant with C99, which states that when a function-like macro ends
 * with ellipsis (...) it should be called with at least one argument for the
 * variable list.
 */
#define ___is_active(arg1_or_junk)    __take_second_arg(arg1_or_junk 1, 0, 0)
 
/* Finally, we just always take the second argument, which will be either 1
 * (when three arguments are passed, i.e. macro was defined as 1) or 0 (when
 * only two arguments are passed).
 */
#define __take_second_arg(__ignored, val, ...) val
#ifdef __cplusplus
}
#endif
 
#endif /* MODULES_H */