include/linux/kconfig.h

#ifndef __LINUX_KCONFIG_H
#define __LINUX_KCONFIG_H

#include <generated/autoconf.h>

#define __ARG_PLACEHOLDER_1 0,
#define __take_second_arg(__ignored, val, ...) val

/*
 * The use of "&&" / "||" is limited in certain expressions.
 * The followings enable to calculate "and" / "or" with macro expansion only.
 */
#define __and(x, y)			___and(x, y)
#define ___and(x, y)			____and(__ARG_PLACEHOLDER_##x, y)
#define ____and(arg1_or_junk, y)	__take_second_arg(arg1_or_junk y, 0)

#define __or(x, y)			___or(x, y)
#define ___or(x, y)			____or(__ARG_PLACEHOLDER_##x, y)
#define ____or(arg1_or_junk, y)		__take_second_arg(arg1_or_junk 1, y)

/*
 * Helper macros to use CONFIG_ options in C/CPP expressions. Note that
 * these only work with boolean and tristate options.
 */

/*
 * Getting something that works in C and CPP for an arg that may or may
 * not be defined is tricky.  Here, if we have "#define CONFIG_BOOGER 1"
 * we match on the placeholder define, insert the "0," for arg1 and generate
 * the triplet (0, 1, 0).  Then the last step cherry picks the 2nd arg (a one).
 * When CONFIG_BOOGER is not defined, we generate a (... 1, 0) pair, and when
 * the last step cherry picks the 2nd arg, we get a zero.
 */
#define config_enabled(cfg)		___is_defined(cfg)
#define __is_defined(x)			___is_defined(x)
#define ___is_defined(val)		____is_defined(__ARG_PLACEHOLDER_##val)
#define ____is_defined(arg1_or_junk)	__take_second_arg(arg1_or_junk 1, 0)

/*
 * IS_BUILTIN(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y', 0
 * otherwise. For boolean options, this is equivalent to
 * IS_ENABLED(CONFIG_FOO).
 */
#define IS_BUILTIN(option) config_enabled(option)

/*
 * IS_MODULE(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'm', 0
 * otherwise.
 */
#define IS_MODULE(option) config_enabled(option##_MODULE)

/*
 * IS_REACHABLE(CONFIG_FOO) evaluates to 1 if the currently compiled
 * code can call a function defined in code compiled based on CONFIG_FOO.
 * This is similar to IS_ENABLED(), but returns false when invoked from
 * built-in code when CONFIG_FOO is set to 'm'.
 */
#define IS_REACHABLE(option) __or(IS_BUILTIN(option), \
				__and(IS_MODULE(option), __is_defined(MODULE)))

/*
 * IS_ENABLED(CONFIG_FOO) evaluates to 1 if CONFIG_FOO is set to 'y' or 'm',
 * 0 otherwise.
 */
#define IS_ENABLED(option) __or(IS_BUILTIN(option), IS_MODULE(option))

#endif /* __LINUX_KCONFIG_H */