elfcpp/elfcpp_swap.h

   1 // elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
   2
   3 // This header file defines basic template classes to efficiently swap
   4 // numbers between host form and target form.  When the host and
   5 // target have the same endianness, these turn into no-ops.
   6
   7 #ifndef ELFCPP_SWAP_H
   8 #define ELFCPP_SWAP_H
   9
  10 #include <stdint.h>
  11 #include <endian.h>
  12 #include <byteswap.h>
  13
  14 namespace elfcpp
  15 {
  16
  17 // Endian simply indicates whether the host is big endian or not.
  18
  19 struct Endian
  20 {
  21  public:
  22   // Used for template specializations.
  23   static const bool host_big_endian = __BYTE_ORDER == __BIG_ENDIAN;
  24 };
  25
  26 // Valtype_base is a template based on size (8, 16, 32, 64) which
  27 // defines the type Valtype as the unsigned integer of the specified
  28 // size.
  29
  30 template<int size>
  31 struct Valtype_base;
  32
  33 template<>
  34 struct Valtype_base<8>
  35 {
  36   typedef unsigned char Valtype;
  37 };
  38
  39 template<>
  40 struct Valtype_base<16>
  41 {
  42   typedef uint16_t Valtype;
  43 };
  44
  45 template<>
  46 struct Valtype_base<32>
  47 {
  48   typedef uint32_t Valtype;
  49 };
  50
  51 template<>
  52 struct Valtype_base<64>
  53 {
  54   typedef uint64_t Valtype;
  55 };
  56
  57 // Convert_endian is a template based on size and on whether the host
  58 // and target have the same endianness.  It defines the type Valtype
  59 // as Valtype_base does, and also defines a function convert_host
  60 // which takes an argument of type Valtype and returns the same value,
  61 // but swapped if the host and target have different endianness.
  62
  63 template<int size, bool same_endian>
  64 struct Convert_endian;
  65
  66 template<int size>
  67 struct Convert_endian<size, true>
  68 {
  69   typedef typename Valtype_base<size>::Valtype Valtype;
  70
  71   static inline Valtype
  72   convert_host(Valtype v)
  73   { return v; }
  74 };
  75
  76 template<>
  77 struct Convert_endian<8, false>
  78 {
  79   typedef Valtype_base<8>::Valtype Valtype;
  80
  81   static inline Valtype
  82   convert_host(Valtype v)
  83   { return v; }
  84 };
  85
  86 template<>
  87 struct Convert_endian<16, false>
  88 {
  89   typedef Valtype_base<16>::Valtype Valtype;
  90
  91   static inline Valtype
  92   convert_host(Valtype v)
  93   { return bswap_16(v); }
  94 };
  95
  96 template<>
  97 struct Convert_endian<32, false>
  98 {
  99   typedef Valtype_base<32>::Valtype Valtype;
 100
 101   static inline Valtype
 102   convert_host(Valtype v)
 103   { return bswap_32(v); }
 104 };
 105
 106 template<>
 107 struct Convert_endian<64, false>
 108 {
 109   typedef Valtype_base<64>::Valtype Valtype;
 110
 111   static inline Valtype
 112   convert_host(Valtype v)
 113   { return bswap_64(v); }
 114 };
 115
 116 // Convert is a template based on size and on whether the target is
 117 // big endian.  It defines Valtype and convert_host like
 118 // Convert_endian.  That is, it is just like Convert_endian except in
 119 // the meaning of the second template parameter.
 120
 121 template<int size, bool big_endian>
 122 struct Convert
 123 {
 124   typedef typename Valtype_base<size>::Valtype Valtype;
 125
 126   static inline Valtype
 127   convert_host(Valtype v)
 128   {
 129     return Convert_endian<size, big_endian == Endian::host_big_endian>
 130       ::convert_host(v);
 131   }
 132 };
 133
 134 // Swap is a template based on size and on whether the target is big
 135 // endian.  It defines the type Valtype and the functions readval and
 136 // writeval.  The functions read and write values of the appropriate
 137 // size out of buffers, swapping them if necessary.  readval and
 138 // writeval are overloaded to take pointers to the appropriate type or
 139 // pointers to unsigned char.
 140
 141 template<int size, bool big_endian>
 142 struct Swap
 143 {
 144   typedef typename Valtype_base<size>::Valtype Valtype;
 145
 146   static inline Valtype
 147   readval(const Valtype* wv)
 148   { return Convert<size, big_endian>::convert_host(*wv); }
 149
 150   static inline void
 151   writeval(Valtype* wv, Valtype v)
 152   { *wv = Convert<size, big_endian>::convert_host(v); }
 153
 154   static inline Valtype
 155   readval(const unsigned char* wv)
 156   { return readval(reinterpret_cast<const Valtype*>(wv)); }
 157
 158   static inline void
 159   writeval(unsigned char* wv, Valtype v)
 160   { writeval(reinterpret_cast<Valtype*>(wv), v); }
 161 };
 162
 163 // We need to specialize the 8-bit version of Swap to avoid
 164 // conflicting overloads, since both versions of readval and writeval
 165 // will have the same type parameters.
 166
 167 template<bool big_endian>
 168 struct Swap<8, big_endian>
 169 {
 170   typedef typename Valtype_base<8>::Valtype Valtype;
 171
 172   static inline Valtype
 173   readval(const Valtype* wv)
 174   { return *wv; }
 175
 176   static inline void
 177   writeval(Valtype* wv, Valtype v)
 178   { *wv = v; }
 179 };
 180
 181 // Swap_unaligned is a template based on size and on whether the
 182 // target is big endian.  It defines the type Valtype and the
 183 // functions readval and writeval.  The functions read and write
 184 // values of the appropriate size out of buffers which may be
 185 // misaligned.
 186
 187 template<int size, bool big_endian>
 188 struct Swap_unaligned;
 189
 190 template<bool big_endian>
 191 struct Swap_unaligned<8, big_endian>
 192 {
 193   typedef typename Valtype_base<8>::Valtype Valtype;
 194
 195   static inline Valtype
 196   readval(const unsigned char* wv)
 197   { return *wv; }
 198
 199   static inline void
 200   writeval(unsigned char* wv, Valtype v)
 201   { *wv = v; }
 202 };
 203
 204 template<>
 205 struct Swap_unaligned<16, false>
 206 {
 207   typedef Valtype_base<16>::Valtype Valtype;
 208
 209   static inline Valtype
 210   readval(const unsigned char* wv)
 211   {
 212     return (wv[1] << 8) | wv[0];
 213   }
 214
 215   static inline void
 216   writeval(unsigned char* wv, Valtype v)
 217   {
 218     wv[1] = v >> 8;
 219     wv[0] = v;
 220   }
 221 };
 222
 223 template<>
 224 struct Swap_unaligned<16, true>
 225 {
 226   typedef Valtype_base<16>::Valtype Valtype;
 227
 228   static inline Valtype
 229   readval(const unsigned char* wv)
 230   {
 231     return (wv[0] << 8) | wv[1];
 232   }
 233
 234   static inline void
 235   writeval(unsigned char* wv, Valtype v)
 236   {
 237     wv[0] = v >> 8;
 238     wv[1] = v;
 239   }
 240 };
 241
 242 template<>
 243 struct Swap_unaligned<32, false>
 244 {
 245   typedef Valtype_base<32>::Valtype Valtype;
 246
 247   static inline Valtype
 248   readval(const unsigned char* wv)
 249   {
 250     return (wv[3] << 24) | (wv[2] << 16) | (wv[1] << 8) | wv[0];
 251   }
 252
 253   static inline void
 254   writeval(unsigned char* wv, Valtype v)
 255   {
 256     wv[3] = v >> 24;
 257     wv[2] = v >> 16;
 258     wv[1] = v >> 8;
 259     wv[0] = v;
 260   }
 261 };
 262
 263 template<>
 264 struct Swap_unaligned<32, true>
 265 {
 266   typedef Valtype_base<32>::Valtype Valtype;
 267
 268   static inline Valtype
 269   readval(const unsigned char* wv)
 270   {
 271     return (wv[0] << 24) | (wv[1] << 16) | (wv[2] << 8) | wv[3];
 272   }
 273
 274   static inline void
 275   writeval(unsigned char* wv, Valtype v)
 276   {
 277     wv[0] = v >> 24;
 278     wv[1] = v >> 16;
 279     wv[2] = v >> 8;
 280     wv[3] = v;
 281   }
 282 };
 283
 284 template<>
 285 struct Swap_unaligned<64, false>
 286 {
 287   typedef Valtype_base<64>::Valtype Valtype;
 288
 289   static inline Valtype
 290   readval(const unsigned char* wv)
 291   {
 292     return ((static_cast<Valtype>(wv[7]) << 56)
 293             | (static_cast<Valtype>(wv[6]) << 48)
 294             | (static_cast<Valtype>(wv[5]) << 40)
 295             | (static_cast<Valtype>(wv[4]) << 32)
 296             | (static_cast<Valtype>(wv[3]) << 24)
 297             | (static_cast<Valtype>(wv[2]) << 16)
 298             | (static_cast<Valtype>(wv[1]) << 8)
 299             | static_cast<Valtype>(wv[0]));
 300   }
 301
 302   static inline void
 303   writeval(unsigned char* wv, Valtype v)
 304   {
 305     wv[7] = v >> 56;
 306     wv[6] = v >> 48;
 307     wv[5] = v >> 40;
 308     wv[4] = v >> 32;
 309     wv[3] = v >> 24;
 310     wv[2] = v >> 16;
 311     wv[1] = v >> 8;
 312     wv[0] = v;
 313   }
 314 };
 315
 316 template<>
 317 struct Swap_unaligned<64, true>
 318 {
 319   typedef Valtype_base<64>::Valtype Valtype;
 320
 321   static inline Valtype
 322   readval(const unsigned char* wv)
 323   {
 324     return ((static_cast<Valtype>(wv[0]) << 56)
 325             | (static_cast<Valtype>(wv[1]) << 48)
 326             | (static_cast<Valtype>(wv[2]) << 40)
 327             | (static_cast<Valtype>(wv[3]) << 32)
 328             | (static_cast<Valtype>(wv[4]) << 24)
 329             | (static_cast<Valtype>(wv[5]) << 16)
 330             | (static_cast<Valtype>(wv[6]) << 8)
 331             | static_cast<Valtype>(wv[7]));
 332   }
 333
 334   static inline void
 335   writeval(unsigned char* wv, Valtype v)
 336   {
 337     wv[7] = v >> 56;
 338     wv[6] = v >> 48;
 339     wv[5] = v >> 40;
 340     wv[4] = v >> 32;
 341     wv[3] = v >> 24;
 342     wv[2] = v >> 16;
 343     wv[1] = v >> 8;
 344     wv[0] = v;
 345   }
 346 };
 347
 348 } // End namespace elfcpp.
 349
 350 #endif // !defined(ELFCPP_SWAP_H)