File: /usr/src/linux/include/asm-arm/unaligned.h
1 #ifndef __ASM_ARM_UNALIGNED_H
2 #define __ASM_ARM_UNALIGNED_H
3
4 #include <asm/types.h>
5
6 extern int __bug_unaligned_x(void *ptr);
7
8 /*
9 * What is the most efficient way of loading/storing an unaligned value?
10 *
11 * That is the subject of this file. Efficiency here is defined as
12 * minimum code size with minimum register usage for the common cases.
13 * It is currently not believed that long longs are common, so we
14 * trade efficiency for the chars, shorts and longs against the long
15 * longs.
16 *
17 * Current stats with gcc 2.7.2.2 for these functions:
18 *
19 * ptrsize get: code regs put: code regs
20 * 1 1 1 1 2
21 * 2 3 2 3 2
22 * 4 7 3 7 3
23 * 8 20 6 16 6
24 *
25 * gcc 2.95.1 seems to code differently:
26 *
27 * ptrsize get: code regs put: code regs
28 * 1 1 1 1 2
29 * 2 3 2 3 2
30 * 4 7 4 7 4
31 * 8 19 8 15 6
32 *
33 * which may or may not be more efficient (depending upon whether
34 * you can afford the extra registers). Hopefully the gcc 2.95
35 * is inteligent enough to decide if it is better to use the
36 * extra register, but evidence so far seems to suggest otherwise.
37 *
38 * Unfortunately, gcc is not able to optimise the high word
39 * out of long long >> 32, or the low word from long long << 32
40 */
41
42 #define __get_unaligned_2(__p) \
43 (__p[0] | __p[1] << 8)
44
45 #define __get_unaligned_4(__p) \
46 (__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24)
47
48 #define get_unaligned(ptr) \
49 ({ \
50 __typeof__(*(ptr)) __v; \
51 __u8 *__p = (__u8 *)(ptr); \
52 switch (sizeof(*(ptr))) { \
53 case 1: __v = *(ptr); break; \
54 case 2: __v = __get_unaligned_2(__p); break; \
55 case 4: __v = __get_unaligned_4(__p); break; \
56 case 8: { \
57 unsigned int __v1, __v2; \
58 __v2 = __get_unaligned_4((__p+4)); \
59 __v1 = __get_unaligned_4(__p); \
60 __v = ((unsigned long long)__v2 << 32 | __v1); \
61 } \
62 break; \
63 default: __v = __bug_unaligned_x(__p); break; \
64 } \
65 __v; \
66 })
67
68
69 static inline void __put_unaligned_2(__u32 __v, register __u8 *__p)
70 {
71 *__p++ = __v;
72 *__p++ = __v >> 8;
73 }
74
75 static inline void __put_unaligned_4(__u32 __v, register __u8 *__p)
76 {
77 __put_unaligned_2(__v >> 16, __p + 2);
78 __put_unaligned_2(__v, __p);
79 }
80
81 static inline void __put_unaligned_8(const unsigned long long __v, register __u8 *__p)
82 {
83 /*
84 * tradeoff: 8 bytes of stack for all unaligned puts (2
85 * instructions), or an extra register in the long long
86 * case - go for the extra register.
87 */
88 __put_unaligned_4(__v >> 32, __p+4);
89 __put_unaligned_4(__v, __p);
90 }
91
92 /*
93 * Try to store an unaligned value as efficiently as possible.
94 */
95 #define put_unaligned(val,ptr) \
96 ({ \
97 switch (sizeof(*(ptr))) { \
98 case 1: \
99 *(ptr) = (val); \
100 break; \
101 case 2: __put_unaligned_2((val),(__u8 *)(ptr)); \
102 break; \
103 case 4: __put_unaligned_4((val),(__u8 *)(ptr)); \
104 break; \
105 case 8: __put_unaligned_8((val),(__u8 *)(ptr)); \
106 break; \
107 default: __bug_unaligned_x(ptr); \
108 break; \
109 } \
110 (void) 0; \
111 })
112
113
114 #endif
115