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112 lines
3.7 KiB
C
112 lines
3.7 KiB
C
/*
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* Copyright (C) 2014 Freie Universität Berlin
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* 2017 HAW-Hamburg
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*
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* This file is subject to the terms and conditions of the GNU Lesser
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* General Public License v2.1. See the file LICENSE in the top level
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* directory for more details.
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*/
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/**
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* @ingroup core_internal
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* @{
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*
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* @file
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* @brief Common macros and compiler attributes/pragmas configuration
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*
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* @author René Kijewski <rene.kijewski@fu-berlin.de>
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* @author Michel Rottleuthner <michel.rottleuthner@haw-hamburg.de>
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*/
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#ifndef MODULES_H
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#define MODULES_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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/**
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* @def IS_ACTIVE(macro)
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* @brief Allows to verify a macro definition outside the preprocessor.
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*
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* @details This macro is based on Linux's clever 'IS_BUILTIN'
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* (https://github.com/torvalds/linux/blob/master/include/linux/kconfig.h).
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* It takes a @p macro value that may be defined to 1 or not even
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* defined (e.g. FEATURE_FOO) and then expands it to an expression
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* that can be used in C code, either 1 or 0.
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*
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* The advantage of using this is that the compiler sees all the
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* code, so checks can be performed, sections that would not be
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* executed are removed during optimization. For example:
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* ```
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* if (IS_ACTIVE(FEATURE_FOO)) {
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* do_something();
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* }
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* ```
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* @param[in] macro Macro to evaluate
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* @returns 1 if the macro is defined to 1
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* @returns 0 if the macro is not defined, of if it is defined to something
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* else than 1.
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*
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* @note This should only be used when macros are defined as 1, it will
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* not work if the macro value is, for example, (1) or 1U.
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*
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* @note Although this may seem to work similarly to the preprocessor's
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* 'defined', it is not entirely equal. If the given macro has
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* been defined with no value, this will expand to 0. Also note
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* that this is intended to be used with 'boolean' macros that act
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* as switches, and usually will be defined as 1 or not defined.
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*/
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#define IS_ACTIVE(macro) __is_active(macro)
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/**
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* @def IS_USED(module)
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* @brief Checks whether a module is being used or not. Can be used in C
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* conditionals.
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*
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* @param[in] module Module to check
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* @returns 1 if the module is being used
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* @returns 0 if the module is not being used
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*/
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#define IS_USED(module) IS_ACTIVE(module)
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/**
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* @cond INTERNAL
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*/
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/* Here a prefix "__PREFIX_WHEN_" is added to the macro. So if it was a 1 we
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* have "__PREFIX_WHEN_1", and if it was not defined we have "__PREFIX_WHEN_".
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*/
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#define __is_active(val) ___is_active(__PREFIX_WHEN_##val)
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/* With this placeholder we turn the original value into two arguments when the
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* original value was defined as 1 (note the comma).
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*/
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#define __PREFIX_WHEN_1 0,
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/* Here we add two extra arguments, that way the next macro can accept varargs.
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*
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* If the original macro was defined as 1, this will have three arguments
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* (__take_second_arg(0, 1, 0, 0)), otherwise it will have two
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* (__take_second_arg(__PREFIX_WHEN_ 1, 0, 0)). The third zero is there just to
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* be compliant with C99, which states that when a function-like macro ends
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* with ellipsis (...) it should be called with at least one argument for the
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* variable list.
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*/
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#define ___is_active(arg1_or_junk) __take_second_arg(arg1_or_junk 1, 0, 0)
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/* Finally, we just always take the second argument, which will be either 1
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* (when three arguments are passed, i.e. macro was defined as 1) or 0 (when
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* only two arguments are passed).
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*/
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#define __take_second_arg(__ignored, val, ...) val
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/**
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* @endcond
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*/
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#ifdef __cplusplus
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}
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#endif
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#endif /* MODULES_H */
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/** @} */
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