| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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_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 | |
| 68 | static inline void __put_unaligned_2_le(__u32 __v, register __u8 *__p) |
| 69 | { |
| 70 | *__p++ = __v; |
| 71 | *__p++ = __v >> 8; |
| 72 | } |
| 73 | |
| 74 | static 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 | |
| 80 | static 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 |