git.oblomov.eu Git - linux-2.6/blob - include/asm-arm26/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_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