tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1#ifndef __ASM_ARM_UNALIGNED_H
2#define __ASM_ARM_UNALIGNED_H
3
4#include <asm/types.h>
5
6extern 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_le(__p) \
43 (__p[0] | __p[1] << 8)
44
45#define __get_unaligned_4_le(__p) \
46 (__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24)
47
48#define __get_unaligned_le(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_le(__p); break; \
55 case 4: __v = __get_unaligned_4_le(__p); break; \
56 case 8: { \
57 unsigned int __v1, __v2; \
58 __v2 = __get_unaligned_4_le((__p+4)); \
59 __v1 = __get_unaligned_4_le(__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
68static inline void __put_unaligned_2_le(__u32 __v, register __u8 *__p)
69{
70 *__p++ = __v;
71 *__p++ = __v >> 8;
72}
73
74static inline void __put_unaligned_4_le(__u32 __v, register __u8 *__p)
75{
76 __put_unaligned_2_le(__v >> 16, __p + 2);
77 __put_unaligned_2_le(__v, __p);
78}
79
80static inline void __put_unaligned_8_le(const unsigned long long __v, register __u8 *__p)
81{
82 /*
83 * tradeoff: 8 bytes of stack for all unaligned puts (2
84 * instructions), or an extra register in the long long
85 * case - go for the extra register.
86 */
87 __put_unaligned_4_le(__v >> 32, __p+4);
88 __put_unaligned_4_le(__v, __p);
89}
90
91/*
92 * Try to store an unaligned value as efficiently as possible.
93 */
94#define __put_unaligned_le(val,ptr) \
95 ({ \
96 switch (sizeof(*(ptr))) { \
97 case 1: \
98 *(ptr) = (val); \
99 break; \
100 case 2: __put_unaligned_2_le((val),(__u8 *)(ptr)); \
101 break; \
102 case 4: __put_unaligned_4_le((val),(__u8 *)(ptr)); \
103 break; \
104 case 8: __put_unaligned_8_le((val),(__u8 *)(ptr)); \
105 break; \
106 default: __bug_unaligned_x(ptr); \
107 break; \
108 } \
109 (void) 0; \
110 })
111
112/*
113 * Select endianness
114 */
115#define get_unaligned __get_unaligned_le
116#define put_unaligned __put_unaligned_le
117
118#endif