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   1 /*
   2  * unaligned.h
   3  *
   4  * Inline functions for unaligned memory accesses.
   5  *
   6  * Author:      Eric Biggers
   7  * Year:        2014, 2015
   8  *
   9  * The author dedicates this file to the public domain.
  10  * You can do whatever you want with this file.
  11  */
  12
  13 #ifndef _WIMLIB_UNALIGNED_H
  14 #define _WIMLIB_UNALIGNED_H
  15
  16 #include "wimlib/compiler.h"
  17 #include "wimlib/endianness.h"
  18 #include "wimlib/types.h"
  19
  20 #define DEFINE_UNALIGNED_TYPE(type)                             \
  21 struct type##_unaligned {                                       \
  22         type v;                                                 \
  23 } _packed_attribute;                                            \
  24                                                                 \
  25 static inline type                                              \
  26 load_##type##_unaligned(const void *p)                          \
  27 {                                                               \
  28         return ((const struct type##_unaligned *)p)->v;         \
  29 }                                                               \
  30                                                                 \
  31 static inline void                                              \
  32 store_##type##_unaligned(type val, void *p)                     \
  33 {                                                               \
  34         ((struct type##_unaligned *)p)->v = val;                \
  35 }
  36
  37 DEFINE_UNALIGNED_TYPE(u16);
  38 DEFINE_UNALIGNED_TYPE(u32);
  39 DEFINE_UNALIGNED_TYPE(u64);
  40 DEFINE_UNALIGNED_TYPE(le16);
  41 DEFINE_UNALIGNED_TYPE(le32);
  42 DEFINE_UNALIGNED_TYPE(le64);
  43 DEFINE_UNALIGNED_TYPE(be16);
  44 DEFINE_UNALIGNED_TYPE(be32);
  45 DEFINE_UNALIGNED_TYPE(be64);
  46 DEFINE_UNALIGNED_TYPE(size_t);
  47 DEFINE_UNALIGNED_TYPE(machine_word_t);
  48
  49 #define load_word_unaligned     load_machine_word_t_unaligned
  50 #define store_word_unaligned    store_machine_word_t_unaligned
  51
  52 static inline u16
  53 get_unaligned_le16(const u8 *p)
  54 {
  55         if (UNALIGNED_ACCESS_IS_FAST)
  56                 return le16_to_cpu(load_le16_unaligned(p));
  57         else
  58                 return ((u16)p[1] << 8) | p[0];
  59 }
  60
  61 static inline u32
  62 get_unaligned_le32(const u8 *p)
  63 {
  64         if (UNALIGNED_ACCESS_IS_FAST)
  65                 return le32_to_cpu(load_le32_unaligned(p));
  66         else
  67                 return ((u32)p[3] << 24) | ((u32)p[2] << 16) |
  68                         ((u32)p[1] << 8) | p[0];
  69 }
  70
  71 static inline void
  72 put_unaligned_le16(u16 v, u8 *p)
  73 {
  74         if (UNALIGNED_ACCESS_IS_FAST) {
  75                 store_le16_unaligned(cpu_to_le16(v), p);
  76         } else {
  77                 p[0] = (u8)(v >> 0);
  78                 p[1] = (u8)(v >> 8);
  79         }
  80 }
  81
  82 static inline void
  83 put_unaligned_le32(u32 v, u8 *p)
  84 {
  85         if (UNALIGNED_ACCESS_IS_FAST) {
  86                 store_le32_unaligned(cpu_to_le32(v), p);
  87         } else {
  88                 p[0] = (u8)(v >> 0);
  89                 p[1] = (u8)(v >> 8);
  90                 p[2] = (u8)(v >> 16);
  91                 p[3] = (u8)(v >> 24);
  92         }
  93 }
  94
  95 /*
  96  * Given a 32-bit value that was loaded with the platform's native endianness,
  97  * return a 32-bit value whose high-order 8 bits are 0 and whose low-order 24
  98  * bits contain the first 3 bytes, arranged in octets in a platform-dependent
  99  * order, at the memory location from which the input 32-bit value was loaded.
 100  */
 101 static inline u32
 102 loaded_u32_to_u24(u32 v)
 103 {
 104         if (CPU_IS_LITTLE_ENDIAN)
 105                 return v & 0xFFFFFF;
 106         else
 107                 return v >> 8;
 108 }
 109
 110 /*
 111  * Load the next 3 bytes from the memory location @p into the 24 low-order bits
 112  * of a 32-bit value.  The order in which the 3 bytes will be arranged as octets
 113  * in the 24 bits is platform-dependent.  At least LOAD_U24_REQUIRED_NBYTES
 114  * bytes must be available at @p; note that this may be more than 3.
 115  */
 116 static inline u32
 117 load_u24_unaligned(const u8 *p)
 118 {
 119 #if UNALIGNED_ACCESS_IS_FAST
 120 #  define LOAD_U24_REQUIRED_NBYTES 4
 121         return loaded_u32_to_u24(load_u32_unaligned(p));
 122 #else
 123 #  define LOAD_U24_REQUIRED_NBYTES 3
 124 #  if CPU_IS_BIG_ENDIAN
 125         return ((u32)p[2] << 0) | ((u32)p[1] << 8) | ((u32)p[0] << 16);
 126 #  else
 127         return ((u32)p[0] << 0) | ((u32)p[1] << 8) | ((u32)p[2] << 16);
 128 #  endif
 129 #endif
 130 }
 131
 132
 133 #endif /* _WIMLIB_UNALIGNED_H */