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