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Diffstat (limited to 'include/asm-arm26/unaligned.h')
| -rw-r--r-- | include/asm-arm26/unaligned.h | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/include/asm-arm26/unaligned.h b/include/asm-arm26/unaligned.h new file mode 100644 index 0000000..d992782 --- /dev/null +++ b/include/asm-arm26/unaligned.h @@ -0,0 +1,118 @@ +#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_le(__p) \ + (__p[0] | __p[1] << 8) + +#define __get_unaligned_4_le(__p) \ + (__p[0] | __p[1] << 8 | __p[2] << 16 | __p[3] << 24) + +#define __get_unaligned_le(ptr) \ + ({ \ + __typeof__(*(ptr)) __v; \ + __u8 *__p = (__u8 *)(ptr); \ + switch (sizeof(*(ptr))) { \ + case 1: __v = *(ptr); break; \ + case 2: __v = __get_unaligned_2_le(__p); break; \ + case 4: __v = __get_unaligned_4_le(__p); break; \ + case 8: { \ + unsigned int __v1, __v2; \ + __v2 = __get_unaligned_4_le((__p+4)); \ + __v1 = __get_unaligned_4_le(__p); \ + __v = ((unsigned long long)__v2 << 32 | __v1); \ + } \ + break; \ + default: __v = __bug_unaligned_x(__p); break; \ + } \ + __v; \ + }) + +static inline void __put_unaligned_2_le(__u32 __v, register __u8 *__p) +{ + *__p++ = __v; + *__p++ = __v >> 8; +} + +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_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); +} + +/* + * Try to store an unaligned value as efficiently as possible. + */ +#define __put_unaligned_le(val,ptr) \ + ({ \ + switch (sizeof(*(ptr))) { \ + case 1: \ + *(ptr) = (val); \ + break; \ + case 2: __put_unaligned_2_le((val),(__u8 *)(ptr)); \ + break; \ + case 4: __put_unaligned_4_le((val),(__u8 *)(ptr)); \ + break; \ + case 8: __put_unaligned_8_le((val),(__u8 *)(ptr)); \ + break; \ + default: __bug_unaligned_x(ptr); \ + break; \ + } \ + (void) 0; \ + }) + +/* + * Select endianness + */ +#define get_unaligned __get_unaligned_le +#define put_unaligned __put_unaligned_le + +#endif |
