endianness.h

//----------------------------------------------------------------------------//
//                                                                            //
// ozz-animation is hosted at http://github.com/guillaumeblanc/ozz-animation  //
// and distributed under the MIT License (MIT).                               //
//                                                                            //
// Copyright (c) Guillaume Blanc                                              //
//                                                                            //
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//----------------------------------------------------------------------------//
 
#ifndef OZZ_OZZ_BASE_ENDIANNESS_H_
#define OZZ_OZZ_BASE_ENDIANNESS_H_
 
// Declares endianness modes and functions to swap data from a mode to another.
 
#include <cstddef>
 
#include "ozz/base/platform.h"
 
namespace ozz {
 
// Declares supported endianness.
enum Endianness {
  kBigEndian,
  kLittleEndian,
};
 
// Get the native endianness of the targeted processor.
// This function does not rely on a pre-processor definition as no standard
// definition exists. It is rather implemented as a portable runtime function.
inline Endianness GetNativeEndianness() {
  const union {
    uint16_t s;
    uint8_t c[2];
  } u = {1};  // Initializes u.s -> then read u.c.
  return Endianness(u.c[0]);
}
 
// Declare the endian swapper struct that is aimed to be specialized (template
// meaning) for every type sizes.
// The swapper provides two functions:
// - void Swap(_Ty* _ty, size_t _count) swaps the array _ty of _count
// elements in-place.
// - _Ty Swap(_Ty _ty) returns a swapped copy of _ty.
// It can be used directly if _Ty is known or through EndianSwap function.
// The default value of template attribute _size enables automatic
// specialization selection.
template <typename _Ty, size_t _size = sizeof(_Ty)>
struct EndianSwapper;
 
// Internal macro used to swap two bytes.
#define OZZ_BYTE_SWAP(_a, _b)    \
  do {                           \
    const ozz::byte temp = (_a); \
    (_a) = (_b);                 \
    (_b) = temp;                 \
  } while (0)
 
// EndianSwapper specialization for 1 byte types.
template <typename _Ty>
struct EndianSwapper<_Ty, 1> {
  OZZ_INLINE static void Swap(_Ty*, size_t) {}
  OZZ_INLINE static _Ty Swap(_Ty _ty) { return _ty; }
};
 
// EndianSwapper specialization for 2 bytes types.
template <typename _Ty>
struct EndianSwapper<_Ty, 2> {
  OZZ_INLINE static void Swap(_Ty* _ty, size_t _count) {
    byte* alias = reinterpret_cast<byte*>(_ty);
    for (size_t i = 0; i < _count * 2; i += 2) {
      OZZ_BYTE_SWAP(alias[i + 0], alias[i + 1]);
    }
  }
  OZZ_INLINE static _Ty Swap(_Ty _ty) {  // Pass by copy to swap _ty in-place.
    byte* alias = reinterpret_cast<byte*>(&_ty);
    OZZ_BYTE_SWAP(alias[0], alias[1]);
    return _ty;
  }
};
 
// EndianSwapper specialization for 4 bytes types.
template <typename _Ty>
struct EndianSwapper<_Ty, 4> {
  OZZ_INLINE static void Swap(_Ty* _ty, size_t _count) {
    byte* alias = reinterpret_cast<byte*>(_ty);
    for (size_t i = 0; i < _count * 4; i += 4) {
      OZZ_BYTE_SWAP(alias[i + 0], alias[i + 3]);
      OZZ_BYTE_SWAP(alias[i + 1], alias[i + 2]);
    }
  }
  OZZ_INLINE static _Ty Swap(_Ty _ty) {  // Pass by copy to swap _ty in-place.
    byte* alias = reinterpret_cast<byte*>(&_ty);
    OZZ_BYTE_SWAP(alias[0], alias[3]);
    OZZ_BYTE_SWAP(alias[1], alias[2]);
    return _ty;
  }
};
 
// EndianSwapper specialization for 8 bytes types.
template <typename _Ty>
struct EndianSwapper<_Ty, 8> {
  OZZ_INLINE static void Swap(_Ty* _ty, size_t _count) {
    byte* alias = reinterpret_cast<byte*>(_ty);
    for (size_t i = 0; i < _count * 8; i += 8) {
      OZZ_BYTE_SWAP(alias[i + 0], alias[i + 7]);
      OZZ_BYTE_SWAP(alias[i + 1], alias[i + 6]);
      OZZ_BYTE_SWAP(alias[i + 2], alias[i + 5]);
      OZZ_BYTE_SWAP(alias[i + 3], alias[i + 4]);
    }
  }
  OZZ_INLINE static _Ty Swap(_Ty _ty) {  // Pass by copy to swap _ty in-place.
    byte* alias = reinterpret_cast<byte*>(&_ty);
    OZZ_BYTE_SWAP(alias[0], alias[7]);
    OZZ_BYTE_SWAP(alias[1], alias[6]);
    OZZ_BYTE_SWAP(alias[2], alias[5]);
    OZZ_BYTE_SWAP(alias[3], alias[4]);
    return _ty;
  }
};
 
// OZZ_BYTE_SWAP is not useful anymore.
#undef OZZ_BYTE_SWAP
 
// Helper function that swaps _count elements of the array _ty in place.
template <typename _Ty>
OZZ_INLINE void EndianSwap(_Ty* _ty, size_t _count) {
  EndianSwapper<_Ty>::Swap(_ty, _count);
}
 
// Helper function that swaps _ty in place.
template <typename _Ty>
OZZ_INLINE _Ty EndianSwap(_Ty _ty) {
  return EndianSwapper<_Ty>::Swap(_ty);
}
}  // namespace ozz
#endif  // OZZ_OZZ_BASE_ENDIANNESS_H_