elfcpp/elfcpp_swap.h

   1 // elfcpp_swap.h -- Handle swapping for elfcpp   -*- C++ -*-
   2
   3 // Copyright 2006, 2007, Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of elfcpp.
   7
   8 // This program is free software; you can redistribute it and/or
   9 // modify it under the terms of the GNU Library General Public License
  10 // as published by the Free Software Foundation; either version 2, or
  11 // (at your option) any later version.
  12
  13 // In addition to the permissions in the GNU Library General Public
  14 // License, the Free Software Foundation gives you unlimited
  15 // permission to link the compiled version of this file into
  16 // combinations with other programs, and to distribute those
  17 // combinations without any restriction coming from the use of this
  18 // file.  (The Library Public License restrictions do apply in other
  19 // respects; for example, they cover modification of the file, and
  20 /// distribution when not linked into a combined executable.)
  21
  22 // This program is distributed in the hope that it will be useful, but
  23 // WITHOUT ANY WARRANTY; without even the implied warranty of
  24 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  25 // Library General Public License for more details.
  26
  27 // You should have received a copy of the GNU Library General Public
  28 // License along with this program; if not, write to the Free Software
  29 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA
  30 // 02110-1301, USA.
  31
  32 // This header file defines basic template classes to efficiently swap
  33 // numbers between host form and target form.  When the host and
  34 // target have the same endianness, these turn into no-ops.
  35
  36 #ifndef ELFCPP_SWAP_H
  37 #define ELFCPP_SWAP_H
  38
  39 #include <stdint.h>
  40 #include <endian.h>
  41 #include <byteswap.h>
  42
  43 namespace elfcpp
  44 {
  45
  46 // Endian simply indicates whether the host is big endian or not.
  47
  48 struct Endian
  49 {
  50  public:
  51   // Used for template specializations.
  52   static const bool host_big_endian = __BYTE_ORDER == __BIG_ENDIAN;
  53 };
  54
  55 // Valtype_base is a template based on size (8, 16, 32, 64) which
  56 // defines the type Valtype as the unsigned integer, and
  57 // Signed_valtype as the signed integer, of the specified size.
  58
  59 template<int size>
  60 struct Valtype_base;
  61
  62 template<>
  63 struct Valtype_base<8>
  64 {
  65   typedef uint8_t Valtype;
  66   typedef int8_t Signed_valtype;
  67 };
  68
  69 template<>
  70 struct Valtype_base<16>
  71 {
  72   typedef uint16_t Valtype;
  73   typedef int16_t Signed_valtype;
  74 };
  75
  76 template<>
  77 struct Valtype_base<32>
  78 {
  79   typedef uint32_t Valtype;
  80   typedef int32_t Signed_valtype;
  81 };
  82
  83 template<>
  84 struct Valtype_base<64>
  85 {
  86   typedef uint64_t Valtype;
  87   typedef int64_t Signed_valtype;
  88 };
  89
  90 // Convert_endian is a template based on size and on whether the host
  91 // and target have the same endianness.  It defines the type Valtype
  92 // as Valtype_base does, and also defines a function convert_host
  93 // which takes an argument of type Valtype and returns the same value,
  94 // but swapped if the host and target have different endianness.
  95
  96 template<int size, bool same_endian>
  97 struct Convert_endian;
  98
  99 template<int size>
 100 struct Convert_endian<size, true>
 101 {
 102   typedef typename Valtype_base<size>::Valtype Valtype;
 103
 104   static inline Valtype
 105   convert_host(Valtype v)
 106   { return v; }
 107 };
 108
 109 template<>
 110 struct Convert_endian<8, false>
 111 {
 112   typedef Valtype_base<8>::Valtype Valtype;
 113
 114   static inline Valtype
 115   convert_host(Valtype v)
 116   { return v; }
 117 };
 118
 119 template<>
 120 struct Convert_endian<16, false>
 121 {
 122   typedef Valtype_base<16>::Valtype Valtype;
 123
 124   static inline Valtype
 125   convert_host(Valtype v)
 126   { return bswap_16(v); }
 127 };
 128
 129 template<>
 130 struct Convert_endian<32, false>
 131 {
 132   typedef Valtype_base<32>::Valtype Valtype;
 133
 134   static inline Valtype
 135   convert_host(Valtype v)
 136   { return bswap_32(v); }
 137 };
 138
 139 template<>
 140 struct Convert_endian<64, false>
 141 {
 142   typedef Valtype_base<64>::Valtype Valtype;
 143
 144   static inline Valtype
 145   convert_host(Valtype v)
 146   { return bswap_64(v); }
 147 };
 148
 149 // Convert is a template based on size and on whether the target is
 150 // big endian.  It defines Valtype and convert_host like
 151 // Convert_endian.  That is, it is just like Convert_endian except in
 152 // the meaning of the second template parameter.
 153
 154 template<int size, bool big_endian>
 155 struct Convert
 156 {
 157   typedef typename Valtype_base<size>::Valtype Valtype;
 158
 159   static inline Valtype
 160   convert_host(Valtype v)
 161   {
 162     return Convert_endian<size, big_endian == Endian::host_big_endian>
 163       ::convert_host(v);
 164   }
 165 };
 166
 167 // Swap is a template based on size and on whether the target is big
 168 // endian.  It defines the type Valtype and the functions readval and
 169 // writeval.  The functions read and write values of the appropriate
 170 // size out of buffers, swapping them if necessary.  readval and
 171 // writeval are overloaded to take pointers to the appropriate type or
 172 // pointers to unsigned char.
 173
 174 template<int size, bool big_endian>
 175 struct Swap
 176 {
 177   typedef typename Valtype_base<size>::Valtype Valtype;
 178
 179   static inline Valtype
 180   readval(const Valtype* wv)
 181   { return Convert<size, big_endian>::convert_host(*wv); }
 182
 183   static inline void
 184   writeval(Valtype* wv, Valtype v)
 185   { *wv = Convert<size, big_endian>::convert_host(v); }
 186
 187   static inline Valtype
 188   readval(const unsigned char* wv)
 189   { return readval(reinterpret_cast<const Valtype*>(wv)); }
 190
 191   static inline void
 192   writeval(unsigned char* wv, Valtype v)
 193   { writeval(reinterpret_cast<Valtype*>(wv), v); }
 194 };
 195
 196 // We need to specialize the 8-bit version of Swap to avoid
 197 // conflicting overloads, since both versions of readval and writeval
 198 // will have the same type parameters.
 199
 200 template<bool big_endian>
 201 struct Swap<8, big_endian>
 202 {
 203   typedef typename Valtype_base<8>::Valtype Valtype;
 204
 205   static inline Valtype
 206   readval(const Valtype* wv)
 207   { return *wv; }
 208
 209   static inline void
 210   writeval(Valtype* wv, Valtype v)
 211   { *wv = v; }
 212 };
 213
 214 // Swap_unaligned is a template based on size and on whether the
 215 // target is big endian.  It defines the type Valtype and the
 216 // functions readval and writeval.  The functions read and write
 217 // values of the appropriate size out of buffers which may be
 218 // misaligned.
 219
 220 template<int size, bool big_endian>
 221 struct Swap_unaligned;
 222
 223 template<bool big_endian>
 224 struct Swap_unaligned<8, big_endian>
 225 {
 226   typedef typename Valtype_base<8>::Valtype Valtype;
 227
 228   static inline Valtype
 229   readval(const unsigned char* wv)
 230   { return *wv; }
 231
 232   static inline void
 233   writeval(unsigned char* wv, Valtype v)
 234   { *wv = v; }
 235 };
 236
 237 template<>
 238 struct Swap_unaligned<16, false>
 239 {
 240   typedef Valtype_base<16>::Valtype Valtype;
 241
 242   static inline Valtype
 243   readval(const unsigned char* wv)
 244   {
 245     return (wv[1] << 8) | wv[0];
 246   }
 247
 248   static inline void
 249   writeval(unsigned char* wv, Valtype v)
 250   {
 251     wv[1] = v >> 8;
 252     wv[0] = v;
 253   }
 254 };
 255
 256 template<>
 257 struct Swap_unaligned<16, true>
 258 {
 259   typedef Valtype_base<16>::Valtype Valtype;
 260
 261   static inline Valtype
 262   readval(const unsigned char* wv)
 263   {
 264     return (wv[0] << 8) | wv[1];
 265   }
 266
 267   static inline void
 268   writeval(unsigned char* wv, Valtype v)
 269   {
 270     wv[0] = v >> 8;
 271     wv[1] = v;
 272   }
 273 };
 274
 275 template<>
 276 struct Swap_unaligned<32, false>
 277 {
 278   typedef Valtype_base<32>::Valtype Valtype;
 279
 280   static inline Valtype
 281   readval(const unsigned char* wv)
 282   {
 283     return (wv[3] << 24) | (wv[2] << 16) | (wv[1] << 8) | wv[0];
 284   }
 285
 286   static inline void
 287   writeval(unsigned char* wv, Valtype v)
 288   {
 289     wv[3] = v >> 24;
 290     wv[2] = v >> 16;
 291     wv[1] = v >> 8;
 292     wv[0] = v;
 293   }
 294 };
 295
 296 template<>
 297 struct Swap_unaligned<32, true>
 298 {
 299   typedef Valtype_base<32>::Valtype Valtype;
 300
 301   static inline Valtype
 302   readval(const unsigned char* wv)
 303   {
 304     return (wv[0] << 24) | (wv[1] << 16) | (wv[2] << 8) | wv[3];
 305   }
 306
 307   static inline void
 308   writeval(unsigned char* wv, Valtype v)
 309   {
 310     wv[0] = v >> 24;
 311     wv[1] = v >> 16;
 312     wv[2] = v >> 8;
 313     wv[3] = v;
 314   }
 315 };
 316
 317 template<>
 318 struct Swap_unaligned<64, false>
 319 {
 320   typedef Valtype_base<64>::Valtype Valtype;
 321
 322   static inline Valtype
 323   readval(const unsigned char* wv)
 324   {
 325     return ((static_cast<Valtype>(wv[7]) << 56)
 326             | (static_cast<Valtype>(wv[6]) << 48)
 327             | (static_cast<Valtype>(wv[5]) << 40)
 328             | (static_cast<Valtype>(wv[4]) << 32)
 329             | (static_cast<Valtype>(wv[3]) << 24)
 330             | (static_cast<Valtype>(wv[2]) << 16)
 331             | (static_cast<Valtype>(wv[1]) << 8)
 332             | static_cast<Valtype>(wv[0]));
 333   }
 334
 335   static inline void
 336   writeval(unsigned char* wv, Valtype v)
 337   {
 338     wv[7] = v >> 56;
 339     wv[6] = v >> 48;
 340     wv[5] = v >> 40;
 341     wv[4] = v >> 32;
 342     wv[3] = v >> 24;
 343     wv[2] = v >> 16;
 344     wv[1] = v >> 8;
 345     wv[0] = v;
 346   }
 347 };
 348
 349 template<>
 350 struct Swap_unaligned<64, true>
 351 {
 352   typedef Valtype_base<64>::Valtype Valtype;
 353
 354   static inline Valtype
 355   readval(const unsigned char* wv)
 356   {
 357     return ((static_cast<Valtype>(wv[0]) << 56)
 358             | (static_cast<Valtype>(wv[1]) << 48)
 359             | (static_cast<Valtype>(wv[2]) << 40)
 360             | (static_cast<Valtype>(wv[3]) << 32)
 361             | (static_cast<Valtype>(wv[4]) << 24)
 362             | (static_cast<Valtype>(wv[5]) << 16)
 363             | (static_cast<Valtype>(wv[6]) << 8)
 364             | static_cast<Valtype>(wv[7]));
 365   }
 366
 367   static inline void
 368   writeval(unsigned char* wv, Valtype v)
 369   {
 370     wv[0] = v >> 56;
 371     wv[1] = v >> 48;
 372     wv[2] = v >> 40;
 373     wv[3] = v >> 32;
 374     wv[4] = v >> 24;
 375     wv[5] = v >> 16;
 376     wv[6] = v >> 8;
 377     wv[7] = v;
 378   }
 379 };
 380
 381 } // End namespace elfcpp.
 382
 383 #endif // !defined(ELFCPP_SWAP_H)