UnitDimension.h

/* Distributed under the Apache License, Version 2.0.
   See accompanying NOTICE file for details.*/
 
//----------------------------------------------------------------------------
//----------------------------------------------------------------------------
#pragma once
 
#include "cdm/utils/unitconversion/CompoundUnitElement.h"
 
// The nth element in our array contains the total exponent of the nth fundamental
// quantity type in the transitive closure of the expansion of each unit in 
// a compound unit structure. The purpose of this object is to determine whether
// two CompoundUnits are dimensionally compatible (i.e. whether one can be converted
// to the other and vice-versa).
 
class CUnitDimension
{
public:
  typedef CCompoundUnitElement::ExponentType ExponentType;
  typedef std::vector<ExponentType> ExponentList;
 
  // Default ctor: size the array according to the number of fundamental quantities
  CUnitDimension();
 
  // Copy ctor. 
  CUnitDimension(const CUnitDimension &src)
    :m_EList(src.m_EList)
  {
 
  };
 
  size_t size() const
  {
    return m_EList.size();
  }
 
  // Vectors of ints are probably initialized to zero anyway upon creation,
  // but I'd rather not rely on that.
  void InitElems();
 
  // Operators that allow CCompoundUnit to construct our elements
  // Always a good idea to overload operator= if providing a copy constructor
  CUnitDimension & operator=(const CUnitDimension &rhs)
  {
    m_EList = rhs.m_EList;
    return *this;
  };
 
  // Provide interface to indexing to the underlying vector elements. Alternative
  // is exposing the vector pointer, which would be somewhat ugly.
  CCompoundUnitElement::ExponentType & operator[](size_t pos)
  {
    return m_EList[pos];
  };
 
  // Not sure if we'd ever need to index into a const CCompoundUnitElement, but
  // completeness is always a good thing.
  CCompoundUnitElement::ExponentType const & operator[](size_t pos) const
  {
    return m_EList[pos];
  };
 
  // Test two CUnitDimension objects for equality. Here's where we want behavior
  // that goes above and beyond what a vector does all by itself. It's conceivable,
  // though unlikely, that application code may add new fundamental quantities
  // after CUnitDimension objects have already been created. Thus, two CUnitDimension
  // objects can be "equal" even if they're not the same size, so long as the longer
  // one has zeros in its elements that are beyond the length of the shorter one.
  bool  operator==(const CUnitDimension &rhs) const
  {
    if (m_EList.size() == rhs.m_EList.size())
    {
      return (m_EList == rhs.m_EList);
    }
    else
    {
      size_t shorter = MIN(m_EList.size(), rhs.m_EList.size());
      size_t longer = MAX(m_EList.size(), rhs.m_EList.size());
      // First compare over elements they have in common
      for (size_t i=0; i<shorter; ++i)
      {
        if (m_EList[i] != rhs.m_EList[i])
        {
          return false;
        }
      }
      // Now figure out which vector is the longer one and check its extra 
      // elements to make sure they're all zero
      const ExponentList &longerList = (m_EList.size()==longer ? m_EList : rhs.m_EList);
      for (size_t i=shorter; i<longer; ++i)
      {
        if (longerList[i] != 0.0)
        {
          return false;
        }
      }
      return true;
    }
  };
 
  // Implement operator!= for sake of completeness
  bool  operator!=(const CUnitDimension &rhs) const
  {
    return ! (*this == rhs);
  }
 
  // Adding and subtracting dimension objects allows us to take shortcuts
  // when multiplying and dividing CCompoundUnit objects whose CUnitDimension
  // objects have already been built
  CUnitDimension & operator+=(const CUnitDimension &rhs)
  {
    size_t shorter = MIN(m_EList.size(), rhs.m_EList.size());
    size_t longer = MAX(m_EList.size(), rhs.m_EList.size());
    // First combine over elements they have in common
    for (size_t i=0; i<shorter; ++i)
    {
      m_EList[i] += rhs.m_EList[i];
    }
 
    // If the right hand side is longer than *this, then resize *this and copy
    // the extra elements
    if ((longer>shorter) && (rhs.m_EList.size()==longer))
    {
      m_EList.resize(longer);
      for (size_t i=shorter; i<longer; ++i)
      {
        m_EList[i] = rhs.m_EList[i];
      }
    } // if we need to copy more
    return *this;
  }
 
  CUnitDimension & operator-=(const CUnitDimension &rhs)
  {
    size_t shorter = MIN(m_EList.size(), rhs.m_EList.size());
    size_t longer = MAX(m_EList.size(), rhs.m_EList.size());
    // First combine over elements they have in common
    for (size_t i=0; i<shorter; ++i)
    {
      m_EList[i] -= rhs.m_EList[i];
    }
 
    // If the right hand side is longer than *this, then resize *this and copy
    // the extra elements
    if ((longer>shorter) && (rhs.m_EList.size()==longer))
    {
      m_EList.resize(longer);
      for (size_t i=shorter; i<longer; ++i)
      {
        m_EList[i] = -rhs.m_EList[i];
      }
    } // if we need to copy more
    return *this;
  }
 
  const CUnitDimension operator+(const CUnitDimension &rhs) const
  {
    return CUnitDimension(*this) += rhs;
  }
 
  const CUnitDimension operator-(const CUnitDimension &rhs) const
  {
    return CUnitDimension(*this) -= rhs;
  }
 
  // Multiplying CUnitDimension by a scalar allows us to take shortcuts when 
  // raising to a power a CCompoundUnit object whose CUnitDimension object 
  // has already been computed
  CUnitDimension & operator*= (const double &rhs)
  {
    size_t len = m_EList.size();
    for (size_t i=0; i<len; ++i)
    {
      m_EList[i] *= rhs;
    }
    return *this;
  }
 
  const CUnitDimension operator* (const double &rhs) const
  {
    return CUnitDimension(*this) *= rhs;
  }
 
 
  // Determine if this UnitDimension object corresponds to a single 
  // specified fundamental quantity
  bool IsFundamentalQuantity(size_t fundIdx) const
  {
    size_t len = m_EList.size();
 
    // Rule out invalid params
    if (fundIdx >= len)
    {
      return false;
    }
 
    int requiredVal;
    for (size_t i=0; i<len; ++i)
    {
      //Must be 1 at the fundamental quantity index location, and zero everywhere else
      requiredVal = ((i == fundIdx) ? 1 : 0);
      if (m_EList[i] != requiredVal)
      {
        return false;
      }
    }
    return true;
  }
 
  // Determine if this UnitDimension object is dimensionless
  bool IsDimensionless() const
  {
    size_t len = m_EList.size();
    for (size_t i=0; i<len; ++i)
    {
      if (m_EList[i] != 0)
      {
        return false;
      }
    }
    return true;
  }
 
  // Since we use CUnitDimension objects as the basis for a hashmap key in 
  // CQuantityConversionKey, we need to implement a couple of methods for 
  // use by the CQuantityConversionKey object to help it implement the 
  // methods it needs in order for the default hash_map templated hash_compare 
  // object to work properly. Specifically, we need "operator<" to be defined 
  // properly, and we need a hash_value function.
 
  bool operator<(const CUnitDimension &rhs) const
  {
    size_t shorter = MIN(m_EList.size(), rhs.m_EList.size());
    size_t longer = MAX(m_EList.size(), rhs.m_EList.size());
    // First compare over elements they have in common
    for (size_t i=0; i<shorter; ++i)
    {
      if (m_EList[i] > rhs.m_EList[i])
      {
        return false;
      }
      else if (m_EList[i] < rhs.m_EList[i])
      {
        return true;
      }
    }
 
    // If we got through the above loop without exiting, then all the
    // elements in common are equal. If the vector lengths are the same,
    // then *all* the elements are equal, and the less-than relationship
    // is false
    if (shorter == longer)
    {
      return false;
    }
 
    // The shorter vector is considered to be padded with zeros.
    // Thus, compare the longer vector's elements to the imaginary
    // zeros on the shorter
    if (m_EList.size() > rhs.m_EList.size())
    {
      // ok, the left side is longer. Compare the excess left-side elements
      // to the imaginary padded zeros
      for (size_t i=shorter; i<longer; ++i)
      {
        if (m_EList[i] > 0.0)
        {
          return false;
        }
        else if (m_EList[i] < 0.0)
        {
          return true;
        }
      }
    } // left side is longer
    else
    {
      // ok, the right side is longer. Compare the excess right-side elements
      // to the imaginary padded zeros
      for (size_t i=shorter; i<longer; ++i)
      {
        if (rhs.m_EList[i] > 0.0)
        {
          return true;
        }
        else if (rhs.m_EList[i] < 0.0)
        {
          return false;
        }
      }
    } // right side is longer
 
    // If we get to this point, then the excess elements are all zeros,
    // which means that the two CUnitDimension objects are equal, which
    // means the less-than relationship is false.
    return false;
  }
 
  // For the sake of completeness only, implement the other relational operators
  bool operator>(const CUnitDimension &rhs) const
  {
    return rhs < *this;
  }
 
  bool operator <=(const CUnitDimension &rhs) const
  {
    return !(*this > rhs);
  }
 
  bool operator >=(const CUnitDimension &rhs) const
  {
    return !(*this < rhs);
  }
 
  // This hash value must be invariant with respect to trailing zeros
  // at the end of the vector. See comment above operator==.
  size_t hash_value() const
  {
    ExponentList::const_iterator iend = m_EList.end();
    ExponentList::const_iterator ibgn = m_EList.begin();
    // Find first trailing zero as new "end"
    while ((iend != ibgn) && *--iend == 0);
    iend++;
 
    // Now invoke the collection hash routine provided in <xhash>
    return _Hash_value(ibgn, iend);
  }
 
private:
  ExponentList m_EList;
 
};
 
// The member function operators work when the right operand is a double, but not
// when the left operand is a double. So write a non-member operator* that
// computes the result by invoking the member operator* with operands in the
// reverse order. This is fine because multiplication of a CUnitDimension and
// a scalar double val is an abelian operation.
inline const CUnitDimension operator* (const double &lhs, const CUnitDimension &rhs)
{
  return rhs * lhs;
}
 
// Overload non_member hash_value on CUnitDimension so that the
// templated hash_compare used by hash_map can call it. 
inline size_t hash_value(const CUnitDimension &ref)
{
  return ref.hash_value();
}
 
namespace std
{
  template<>
  struct hash<CUnitDimension>
  {
    size_t operator()(const CUnitDimension& ref) const
    {
      return ref.hash_value();
    }
  };
}