UT_LabeledCapacity.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 * NAME:        UT_LabeledCapacity.h (UT Library, C++)
 *
 * COMMENTS: 
 *     UT_LabeledCapacity has utilities to efficiently store the capacity of
 *     a data buffer along with a label that indicates whether the capacity is 
 *     owned or external.
 *
 *     This code is used in the implementation of UT_Array.h.
 *     It has been put in its own header to prevent the
 *     UT_Array.h header from getting too cluttered.
 */

#ifndef __UT_LABELED_CAPACITY_H_INCLUDED__
#define __UT_LABELED_CAPACITY_H_INCLUDED__

#include <type_traits>

using UT_LabeledCapacityRep = std::make_unsigned_t< exint >;

constexpr UT_LabeledCapacityRep LABELED_CAPACITY_FLAG_EXTERNAL = UT_LabeledCapacityRep( 1 ) << ( ( sizeof( UT_LabeledCapacityRep ) * 8 ) - 1 );
constexpr UT_LabeledCapacityRep LABELED_CAPACITY_MASK_VALUE    = LABELED_CAPACITY_FLAG_EXTERNAL - 1;

class UT_LabeledCapacity
{
public:

private:
    UT_LabeledCapacityRep myRep;
    
    constexpr explicit UT_LabeledCapacity( const UT_LabeledCapacityRep rep ) noexcept :
        myRep( rep )
    {
    }
    
    friend constexpr UT_LabeledCapacity ownedLabeledCapacity( const exint capacity ) noexcept;
    friend constexpr UT_LabeledCapacity externalLabeledCapacity( const exint capacity ) noexcept;
    friend constexpr exint capacityValue( const UT_LabeledCapacity& a ) noexcept;
};

constexpr UT_LabeledCapacity ownedLabeledCapacity( const exint capacity ) noexcept
{        
    UT_ASSERT_P( capacity >= 0 );
    UT_ASSERT_P( ( capacity & LABELED_CAPACITY_MASK_VALUE ) == capacity );
   
    // Don't set the external bit:
    return UT_LabeledCapacity( capacity );
}

constexpr UT_LabeledCapacity externalLabeledCapacity( const exint capacity ) noexcept
{
    UT_ASSERT_P( capacity >= 0 );
    UT_ASSERT_P( ( capacity & LABELED_CAPACITY_MASK_VALUE ) == capacity );

    // Set the external bit:
    return UT_LabeledCapacity( capacity | LABELED_CAPACITY_FLAG_EXTERNAL );
};
    
constexpr exint capacityValue( const UT_LabeledCapacity& a ) noexcept
{
    return a.myRep & LABELED_CAPACITY_MASK_VALUE;
}

#endif