etl/smallest.h

///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl

Copyright(c) 2014 jwellbelove

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#ifndef __ETL_SMALLEST__
#define __ETL_SMALLEST__

#include <stdint.h>

#include "integral_limits.h"

///\defgroup smallest smallest
///\ingroup utilities

namespace etl
{
  //***************************************************************************
  /// Template to determine the smallest type and size.
  /// Supports up to 16 types.
  /// Defines 'value_type' which is the type of the smallest parameter.
  /// Defines 'size' which is the size of the smallest parameter.
  ///\ingroup smallest
  //***************************************************************************
  template <typename T1,         typename T2  = void, typename T3  = void, typename T4  = void,
            typename T5  = void, typename T6  = void, typename T7  = void, typename T8  = void,
            typename T9  = void, typename T10 = void, typename T11 = void, typename T12 = void,
            typename T13 = void, typename T14 = void, typename T15 = void, typename T16 = void>
  struct smallest_type
  {
  private:

    // Declaration.
    template <const bool Boolean, typename TrueType, typename FalseType>
    struct choose_type;

    // Specialisation for 'true'.
    // Defines 'type' as 'TrueType'.
    template <typename TrueType, typename FalseType>
    struct choose_type<true, TrueType, FalseType>
    {
      typedef TrueType type;
    };

    // Specialisation for 'false'. 
    // Defines 'type' as 'FalseType'.
    template <typename TrueType, typename FalseType>
    struct choose_type<false, TrueType, FalseType>
    {
      typedef FalseType type;
    };

  public:

    // Define 'smallest_other' as 'smallest_type' with all but the first parameter. 
    typedef typename smallest_type<T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16>::type smallest_other;

    // Set 'type' to be the smallest of the first parameter and any of the others.
    // This is recursive.
    typedef typename choose_type<(sizeof(T1) < sizeof(smallest_other)),// Boolean
                                  T1,                                  // TrueType
                                  smallest_other>                      // FalseType
                                  ::type type;                         // The smallest type of the two.

    // The size of the smallest type.
    enum
    {
      size = sizeof(type)
    };
  };

  //***************************************************************************
  // Specialisation for one template parameter.
  //***************************************************************************
  template <typename T1>
  struct smallest_type <T1,   void, void, void,
                        void, void, void, void,
                        void, void, void, void,
                        void, void, void, void>
  {
    typedef T1 type;

    enum
    {
      size = sizeof(type)
    };
  };
  
  namespace __private_smallest__
  {
    //*************************************************************************
    // Determine the type to hold the number of bits based on the index.
    //*************************************************************************
    template <const int index>
    struct best_fit_uint_type;
    
    //*************************************************************************
    // Less than or equal to 8 bits.
    //*************************************************************************
    template <>
    struct best_fit_uint_type<0>
    {
      typedef uint_least8_t type;
    };

    //*************************************************************************
    // 9 to 16 bits.
    //*************************************************************************
    template <>
    struct best_fit_uint_type<1>
    {
      typedef uint_least16_t type;
    };

    //*************************************************************************
    // 17 to 31 bits.
    //*************************************************************************
    template <>
    struct best_fit_uint_type<2>
    {
      typedef uint_least32_t type;
    };

    //*************************************************************************
    // Greater than 32 bits.
    //*************************************************************************
    template <>
    struct best_fit_uint_type<3>
    {
      typedef uint_least64_t type;
    };
  }

  //***************************************************************************
  /// Template to determine the smallest unsigned int type that can contain a 
  /// value with the specified number of bits.
  /// Defines 'type' which is the type of the smallest unsigned integer.
  ///\ingroup smallest
  //***************************************************************************
  template <const size_t N>
  struct smallest_uint_for_bits
  {
  private:
    
    // Determines the index of the best unsigned type for the required number of bits.
    static const int TYPE_INDEX = ((N >  8) ? 1 : 0) + ((N > 16) ? 1 : 0) + ((N > 32) ? 1 : 0);

  public:

    typedef typename __private_smallest__::best_fit_uint_type<TYPE_INDEX>::type type;
  };
}

#endif