endianness.h

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/******************************************************************************
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Embedded Template Library.
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https://www.etlcpp.com
 
Copyright(c) 2014 John Wellbelove
 
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#ifndef ETL_ENDIAN_INCLUDED
#define ETL_ENDIAN_INCLUDED
 
#include "platform.h"
#include "binary.h"
#include "enum_type.h"
 
#include <stdint.h>
 
#if ETL_USING_CPP20 && ETL_USING_STL
  #include <bit>
#endif

 
// Have we not already defined ETL_ENDIAN_NATIVE?
#if !defined(ETL_ENDIAN_NATIVE)
  // Can we use the C++20 definitions?
  #if ETL_USING_CPP20 && ETL_USING_STL
    #define ETL_ENDIAN_LITTLE static_cast<int>(std::endian::little)
    #define ETL_ENDIAN_BIG    static_cast<int>(std::endian::big)
    #define ETL_ENDIAN_NATIVE static_cast<int>(std::endian::native)
  // Is this the IAR compiler?
  #elif defined(ETL_COMPILER_IAR) && defined(__LITTLE_ENDIAN__)
    #define ETL_ENDIAN_LITTLE 0
    #define ETL_ENDIAN_BIG    1
    #if __LITTLE_ENDIAN__ == 1
      #define ETL_ENDIAN_NATIVE ETL_ENDIAN_LITTLE
    #elif __LITTLE_ENDIAN__ == 0
      #define ETL_ENDIAN_NATIVE ETL_ENDIAN_BIG
    #endif
  // If not can we use the compiler macros?
  #elif defined(__BYTE_ORDER__)
    // Test the two versions of the macro we are likely to see.
    #if defined(__ORDER_LITTLE_ENDIAN__)
      #define ETL_ENDIAN_LITTLE __ORDER_LITTLE_ENDIAN__
      #define ETL_ENDIAN_BIG    __ORDER_BIG_ENDIAN__
      #define ETL_ENDIAN_NATIVE __BYTE_ORDER__
    #elif defined(__LITTLE_ENDIAN__)
      #define ETL_ENDIAN_LITTLE __LITTLE_ENDIAN__
      #define ETL_ENDIAN_BIG    __BIG_ENDIAN__
      #define ETL_ENDIAN_NATIVE __BYTE_ORDER__
    #endif
  #else
    // The user needs to define ETL_ENDIAN_NATIVE.
    #error Unable to determine native endianness at compile time. ETL_ENDIAN_NATIVE must be defined either as 0 for 'little endian' or 1 for 'big endian'.
  #endif
#else
  // Default values for little and big endianness.
  #define ETL_ENDIAN_LITTLE 0
  #define ETL_ENDIAN_BIG    1
#endif
 
// If true, then the endianness of the platform can be constexpr.
#if (ETL_USING_CPP11 && defined(ETL_ENDIAN_NATIVE))
  #define ETL_HAS_CONSTEXPR_ENDIANNESS 1
#else
  #define ETL_HAS_CONSTEXPR_ENDIANNESS 0
#endif
 
namespace etl
{
  //***************************************************************************
  //***************************************************************************
  struct endian
  {
    enum enum_type
    {
      little = ETL_ENDIAN_LITTLE,
      big    = ETL_ENDIAN_BIG,
      native = ETL_ENDIAN_NATIVE
    };
 
    ETL_DECLARE_ENUM_TYPE(endian, int)
    ETL_ENUM_TYPE(little, "little")
    ETL_ENUM_TYPE(big,    "big")
    ETL_END_ENUM_TYPE
  };
 
  //***************************************************************************
  //***************************************************************************
  struct endianness
  {
    etl::endian operator()() const
    {
      return etl::endian(*this);
    }
 
#if ETL_HAS_CONSTEXPR_ENDIANNESS
    ETL_CONSTEXPR
#endif
      operator etl::endian() const
    {
      return get();
    }
 
#if ETL_HAS_CONSTEXPR_ENDIANNESS
    static ETL_CONSTEXPR etl::endian value()
#else
    static etl::endian value()
#endif
    {
      return get();
    }
 
  private:
 
#if ETL_HAS_CONSTEXPR_ENDIANNESS
    static ETL_CONSTEXPR etl::endian get()
    {
      return etl::endian::native;
    }
#else
    static etl::endian get()
    {
      static const uint32_t i = 0xFFFF0000;
 
      return (*reinterpret_cast<const unsigned char*>(&i) == 0) ? etl::endian::little : etl::endian::big;
    }
#endif
  };
 
  //***************************************************************************
  template <typename T>
  ETL_CONSTEXPR14 typename etl::enable_if<etl::is_integral<T>::value, T>::type ntoh(T value)
  {
    if (endianness::value() == endian::little)
    {
      return etl::reverse_bytes(value);
    }
    else
    {
      return value;
    }
  }
 
  //***************************************************************************
  template <typename T>
  ETL_CONSTEXPR14 typename etl::enable_if<etl::is_integral<T>::value, T>::type hton(T value)
  {
    if (endianness::value() == endian::little)
    {
      return etl::reverse_bytes(value);
    }
    else
    {
      return value;
    }
  }
} // namespace etl
 
#endif