Viewing file:  unaligned.h (2.92 KB) -rw-r--r--
Select action/file-type:
 (+) |  (+) |  (+) | Code (+) | Session (+) |  (+) | SDB (+) |  (+) |  (+) |  (+) |  (+) |  (+) |
#ifndef __ASM_ARM_UNALIGNED_H
#define __ASM_ARM_UNALIGNED_H
#include <asm/types.h>
extern int __bug_unaligned_x(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(__p) \
(__p[0] | __p[1] << 8)
#define __get_unaligned_4(__p) \
(__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24)
#define get_unaligned(ptr) \
({ \
__typeof__(*(ptr)) __v; \
__u8 *__p = (__u8 *)(ptr); \
switch (sizeof(*(ptr))) { \
case 1: __v = *(ptr); break; \
case 2: __v = __get_unaligned_2(__p); break; \
case 4: __v = __get_unaligned_4(__p); break; \
case 8: { \
unsigned int __v1, __v2; \
__v2 = __get_unaligned_4((__p+4)); \
__v1 = __get_unaligned_4(__p); \
__v = ((unsigned long long)__v2 << 32 | __v1); \
} \
break; \
default: __v = __bug_unaligned_x(__p); break; \
} \
__v; \
})
static inline void __put_unaligned_2(__u32 __v, register __u8 *__p)
{
*__p++ = __v;
*__p++ = __v >> 8;
}
static inline void __put_unaligned_4(__u32 __v, register __u8 *__p)
{
__put_unaligned_2(__v >> 16, __p + 2);
__put_unaligned_2(__v, __p);
}
static inline void __put_unaligned_8(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(__v >> 32, __p+4);
__put_unaligned_4(__v, __p);
}
/*
* Try to store an unaligned value as efficiently as possible.
*/
#define put_unaligned(val,ptr) \
({ \
switch (sizeof(*(ptr))) { \
case 1: \
*(ptr) = (val); \
break; \
case 2: __put_unaligned_2((val),(__u8 *)(ptr)); \
break; \
case 4: __put_unaligned_4((val),(__u8 *)(ptr)); \
break; \
case 8: __put_unaligned_8((val),(__u8 *)(ptr)); \
break; \
default: __bug_unaligned_x(ptr); \
break; \
} \
(void) 0; \
})
#endif
|