unaligned.h

来自「linux 内核源代码」· C头文件 代码 · 共 182 行

#ifndef __ASM_ARM_UNALIGNED_H
#define __ASM_ARM_UNALIGNED_H

#include <asm/types.h>

extern int __bug_unaligned_x(const void *ptr);

/*
 * What is the most efficient way of loading/storing an unaligned value?
 *
 * That is the subject of this file.  Efficiency here is defined as
 * minimum code size with minimum register usage for the common cases.
 * It is currently not believed that long longs are common, so we
 * trade efficiency for the chars, shorts and longs against the long
 * longs.
 *
 * Current stats with gcc 2.7.2.2 for these functions:
 *
 *	ptrsize	get:	code	regs	put:	code	regs
 *	1		1	1		1	2
 *	2		3	2		3	2
 *	4		7	3		7	3
 *	8		20	6		16	6
 *
 * gcc 2.95.1 seems to code differently:
 *
 *	ptrsize	get:	code	regs	put:	code	regs
 *	1		1	1		1	2
 *	2		3	2		3	2
 *	4		7	4		7	4
 *	8		19	8		15	6
 *
 * which may or may not be more efficient (depending upon whether
 * you can afford the extra registers).  Hopefully the gcc 2.95
 * is inteligent enough to decide if it is better to use the
 * extra register, but evidence so far seems to suggest otherwise.
 *
 * Unfortunately, gcc is not able to optimise the high word
 * out of long long >> 32, or the low word from long long << 32
 */

#define __get_unaligned_2_le(__p)					\
	(__p[0] | __p[1] << 8)

#define __get_unaligned_2_be(__p)					\
	(__p[0] << 8 | __p[1])

#define __get_unaligned_4_le(__p)					\
	(__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24)

#define __get_unaligned_4_be(__p)					\
	(__p[0] << 24 | __p[1] << 16 | __p[2] << 8 | __p[3])

#define __get_unaligned_8_le(__p)					\
	((unsigned long long)__get_unaligned_4_le((__p+4)) << 32 |	\
		__get_unaligned_4_le(__p))

#define __get_unaligned_8_be(__p)					\
	((unsigned long long)__get_unaligned_4_be(__p) << 32 |		\
		__get_unaligned_4_be((__p+4)))

#define __get_unaligned_le(ptr)						\
	((__force typeof(*(ptr)))({					\
		const __u8 *__p = (const __u8 *)(ptr);			\
		__builtin_choose_expr(sizeof(*(ptr)) == 1, *__p,	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 2, __get_unaligned_2_le(__p),	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 4, __get_unaligned_4_le(__p),	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 8, __get_unaligned_8_le(__p),	\
		    (void)__bug_unaligned_x(__p)))));			\
	}))

#define __get_unaligned_be(ptr)						\
	((__force typeof(*(ptr)))({					\
		const __u8 *__p = (const __u8 *)(ptr);			\
		__builtin_choose_expr(sizeof(*(ptr)) == 1, *__p,	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 2, __get_unaligned_2_be(__p),	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 4, __get_unaligned_4_be(__p),	\
		  __builtin_choose_expr(sizeof(*(ptr)) == 8, __get_unaligned_8_be(__p),	\
		    (void)__bug_unaligned_x(__p)))));			\
	}))


static inline void __put_unaligned_2_le(__u32 __v, register __u8 *__p)
{
	*__p++ = __v;
	*__p++ = __v >> 8;
}

static inline void __put_unaligned_2_be(__u32 __v, register __u8 *__p)
{
	*__p++ = __v >> 8;
	*__p++ = __v;
}

static inline void __put_unaligned_4_le(__u32 __v, register __u8 *__p)
{
	__put_unaligned_2_le(__v >> 16, __p + 2);
	__put_unaligned_2_le(__v, __p);
}

static inline void __put_unaligned_4_be(__u32 __v, register __u8 *__p)
{
	__put_unaligned_2_be(__v >> 16, __p);
	__put_unaligned_2_be(__v, __p + 2);
}

static inline void __put_unaligned_8_le(const unsigned long long __v, register __u8 *__p)
{
	/*
	 * tradeoff: 8 bytes of stack for all unaligned puts (2
	 * instructions), or an extra register in the long long
	 * case - go for the extra register.
	 */
	__put_unaligned_4_le(__v >> 32, __p+4);
	__put_unaligned_4_le(__v, __p);
}

static inline void __put_unaligned_8_be(const unsigned long long __v, register __u8 *__p)
{
	/*
	 * tradeoff: 8 bytes of stack for all unaligned puts (2
	 * instructions), or an extra register in the long long
	 * case - go for the extra register.
	 */
	__put_unaligned_4_be(__v >> 32, __p);
	__put_unaligned_4_be(__v, __p+4);
}

/*
 * Try to store an unaligned value as efficiently as possible.
 */
#define __put_unaligned_le(val,ptr)					\
	({							\
		(void)sizeof(*(ptr) = (val));			\
		switch (sizeof(*(ptr))) {			\
		case 1:						\
			*(ptr) = (val);				\
			break;					\
		case 2: __put_unaligned_2_le((__force u16)(val),(__u8 *)(ptr));	\
			break;					\
		case 4:	__put_unaligned_4_le((__force u32)(val),(__u8 *)(ptr));	\
			break;					\
		case 8:	__put_unaligned_8_le((__force u64)(val),(__u8 *)(ptr)); \
			break;					\
		default: __bug_unaligned_x(ptr);		\
			break;					\
		}						\
		(void) 0;					\
	})

#define __put_unaligned_be(val,ptr)					\
	({							\
		(void)sizeof(*(ptr) = (val));			\
		switch (sizeof(*(ptr))) {			\
		case 1:						\
			*(ptr) = (val);				\
			break;					\
		case 2: __put_unaligned_2_be((__force u16)(val),(__u8 *)(ptr));	\
			break;					\
		case 4:	__put_unaligned_4_be((__force u32)(val),(__u8 *)(ptr));	\
			break;					\
		case 8:	__put_unaligned_8_be((__force u64)(val),(__u8 *)(ptr)); \
			break;					\
		default: __bug_unaligned_x(ptr);		\
			break;					\
		}						\
		(void) 0;					\
	})

/*
 * Select endianness
 */
#ifndef __ARMEB__
#define get_unaligned	__get_unaligned_le
#define put_unaligned	__put_unaligned_le
#else
#define get_unaligned	__get_unaligned_be
#define put_unaligned	__put_unaligned_be
#endif

#endif