C语言常用工具函数

整数

/* atf/include/lib/utils_def.h */
/*
 * This variant of div_round_up can be used in macro definition but should not
 * be used in C code as the `div` parameter is evaluated twice.
 */
#define DIV_ROUND_UP_2EVAL(n, d)	(((n) + (d) - 1) / (d))

#define div_round_up(val, div) __extension__ ({	\
	__typeof__(div) _div = (div);		\
	((val) + _div - (__typeof__(div)) 1) / _div;		\
})

#define MIN(x, y) __extension__ ({	\
	__typeof__(x) _x = (x);		\
	__typeof__(y) _y = (y);		\
	(void)(&_x == &_y);		\
	_x < _y ? _x : _y;		\
})

#define MAX(x, y) __extension__ ({	\
	__typeof__(x) _x = (x);		\
	__typeof__(y) _y = (y);		\
	(void)(&_x == &_y);		\
	_x > _y ? _x : _y;		\
})

#define CLAMP(x, min, max) __extension__ ({ \
	__typeof__(x) _x = (x); \
	__typeof__(min) _min = (min); \
	__typeof__(max) _max = (max); \
	(void)(&_x == &_min); \
	(void)(&_x == &_max); \
	(_x > _max ? _max : (_x < _min ? _min : _x)); \
})

bit操作

/* u-boot/include/linux/bitops.h */

#ifndef BITOPS_H
#define BITOPS_H

#define BITS_PER_BYTE     8
#define BITS_PER_LONG     32

#define BIT(nr)			(1UL << (nr))
#define BIT_ULL(nr)		(1ULL << (nr))
#define BIT_MASK(nr)		(1UL << ((nr) % BITS_PER_LONG))
#define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
#define BIT_ULL_MASK(nr)	(1ULL << ((nr) % BITS_PER_LONG_LONG))
#define BIT_ULL_WORD(nr)	((nr) / BITS_PER_LONG_LONG)
#define BITS_TO_LONGS(nr)	DIV_ROUND_UP(nr, BITS_PER_BYTE * sizeof(long))

/*
 * Create a contiguous bitmask starting at bit position @l and ending at
 * position @h. For example
 * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
 */
#define GENMASK(h, l) \
	(((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))

#define GENMASK_ULL(h, l) \
	(((~0ULL) << (l)) & (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))

#endif

数组

/* Compute the number of elements in the given array */
#define ARRAY_SIZE(a)				\
	(sizeof(a) / sizeof((a)[0]))

#define IS_POWER_OF_TWO(x)			\
	(((x) & ((x) - 1)) == 0)

汇编 -> C语音

/*
 * Import an assembly or linker symbol as a C expression with the specified
 * type
 */
#define IMPORT_SYM(type, sym, name) \
	extern char sym[];\
	static const __attribute__((unused)) type name = (type) sym;

Ref

• Linux

include/linux/bits.h

• Uboot

include/linux/bitops.h

• ATF

include/lib/utils_def.h
include/lib/mmio.h