wimlib.net Git - wimlib/blob - include/wimlib/unaligned.h

   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_u16_le(const void *p)
  54 {
  55         u16 v;
  56
  57         if (UNALIGNED_ACCESS_IS_FAST) {
  58                 v = le16_to_cpu(load_le16_unaligned(p));
  59         } else {
  60                 const u8 *p8 = p;
  61                 v = 0;
  62                 v |= (u16)p8[0] << 0;
  63                 v |= (u16)p8[1] << 8;
  64         }
  65         return v;
  66 }
  67
  68 static inline u32
  69 get_unaligned_u32_le(const void *p)
  70 {
  71         u32 v;
  72
  73         if (UNALIGNED_ACCESS_IS_FAST) {
  74                 v = le32_to_cpu(load_le32_unaligned(p));
  75         } else {
  76                 const u8 *p8 = p;
  77                 v = 0;
  78                 v |= (u32)p8[0] << 0;
  79                 v |= (u32)p8[1] << 8;
  80                 v |= (u32)p8[2] << 16;
  81                 v |= (u32)p8[3] << 24;
  82         }
  83         return v;
  84 }
  85
  86 static inline void
  87 put_unaligned_u16_le(u16 v, void *p)
  88 {
  89         if (UNALIGNED_ACCESS_IS_FAST) {
  90                 store_le16_unaligned(cpu_to_le16(v), p);
  91         } else {
  92                 u8 *p8 = p;
  93                 p8[0] = (v >> 0) & 0xFF;
  94                 p8[1] = (v >> 8) & 0xFF;
  95         }
  96 }
  97
  98 static inline void
  99 put_unaligned_u32_le(u32 v, void *p)
 100 {
 101         if (UNALIGNED_ACCESS_IS_FAST) {
 102                 store_le32_unaligned(cpu_to_le32(v), p);
 103         } else {
 104                 u8 *p8 = p;
 105                 p8[0] = (v >> 0) & 0xFF;
 106                 p8[1] = (v >> 8) & 0xFF;
 107                 p8[2] = (v >> 16) & 0xFF;
 108                 p8[3] = (v >> 24) & 0xFF;
 109         }
 110 }
 111
 112 /*
 113  * Given a 32-bit value that was loaded with the platform's native endianness,
 114  * return a 32-bit value whose high-order 8 bits are 0 and whose low-order 24
 115  * bits contain the first 3 bytes, arranged in octets in a platform-dependent
 116  * order, at the memory location from which the input 32-bit value was loaded.
 117  */
 118 static inline u32
 119 loaded_u32_to_u24(u32 v)
 120 {
 121         if (CPU_IS_LITTLE_ENDIAN)
 122                 return v & 0xFFFFFF;
 123         else
 124                 return v >> 8;
 125 }
 126
 127 /*
 128  * Load the next 3 bytes from the memory location @p into the 24 low-order bits
 129  * of a 32-bit value.  The order in which the 3 bytes will be arranged as octets
 130  * in the 24 bits is platform-dependent.  At least LOAD_U24_REQUIRED_NBYTES
 131  * bytes must be available at @p; note that this may be more than 3.
 132  */
 133 static inline u32
 134 load_u24_unaligned(const u8 *p)
 135 {
 136 #if UNALIGNED_ACCESS_IS_FAST
 137 #  define LOAD_U24_REQUIRED_NBYTES 4
 138         return loaded_u32_to_u24(load_u32_unaligned(p));
 139 #else
 140 #  define LOAD_U24_REQUIRED_NBYTES 3
 141         return ((u32)p[0] << 0) | ((u32)p[1] << 8) | ((u32)p[2] << 16);
 142 #endif
 143 }
 144
 145
 146 #endif /* _WIMLIB_UNALIGNED_H */