CaseSelector.h

Go to the documentation of this file.

/*******************************************************************************
 *
 * Copyright (c) 2008-2010 Michael Schulze <mschulze@ivs.cs.uni-magdeburg.de>
 *                    2010 Marcus Foerster <MarcusFoerster1@gmx.de>
 * All rights reserved.
 *
 *    Redistribution and use in source and binary forms, with or without
 *    modification, are permitted provided that the following conditions
 *    are met:
 *
 *    * Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer.
 *
 *    * Redistributions in binary form must reproduce the above copyright
 *      notice, this list of conditions and the following disclaimer in
 *      the documentation and/or other materials provided with the
 *      distribution.
 *
 *    * Neither the name of the copyright holders nor the names of
 *      contributors may be used to endorse or promote products derived
 *      from this software without specific prior written permission.
 *
 *
 *    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 *    IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 *    TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 *    PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 *    OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *    DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *    (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 *    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * $Id$
 *
 ******************************************************************************/

#ifndef _Case_Selector_
#define _Case_Selector_

#include <stdint.h>

#include "config/type_traits/ByteCount.h"

#include "mw/attributes/detail/AttributeElementHeader.h"
#include "mw/attributes/detail/HighDensityIDs.h"

namespace famouso {
    namespace mw {
        namespace attributes {
            namespace detail {

                template <typename ResultType, ResultType res1, ResultType res2,
                          ResultType res3, ResultType res4, ResultType res5, ResultType res6>
                struct CaseSelector {
                        typedef CaseSelector type;

                        // TODO: This could be a static method, the static constants which are
                        //  calculated below could be members of an inner struct very similar to
                        //  this one and the method only needs to access these; The interface is
                        //  a lot simpler to explain if this is a method
                        template <typename Attr>
                        struct select_ct {
                            private:
                                // The number of bits used by the attribute's value
                                static const uint16_t bitCount = BitCount<typename Attr::value_type,
                                                                          Attr::value>::value;

                                // The whole bytes used by the attribute's value
                                static const uint16_t byteCount = ByteCount<typename Attr::value_type,
                                                                            Attr::value>::value;

                            public:
                                static const ResultType value =
                                    (Attr::highDensity) ?
                                        ( // For high density attributes
                                            (bitCount < 3) ?
                                                // If the value fits the header byte unextended, this is
                                                //  the first case
                                                res1 :

                                                // Check if the value can be written directly (without
                                                //  a length)
                                                (bitCount < 11) ?

                                                    // If the value fits 10 bits (2 bits of the header
                                                    //  byte and 8 bits of the extension) this is the
                                                    //  second case
                                                    res2 :

                                                    // If the length fits the header byte unextended,
                                                    //  we would write the header byte + "length-many"
                                                    //  bytes (Length-values up to 3 fit into two bits,
                                                    //  which would be remaining)
                                                    (byteCount < 4) ?

                                                        // So this is the third case
                                                        res3 :

                                                        // Otherwise we would extend the header byte
                                                        //  and so need one more byte which is the fourth
                                                        //  case
                                                        res4) :

                                        ( // For low density attributes

                                            // The last part of the header byte is always the length, we
                                            //  now must find out, if the header must be extended for the
                                            //  length
                                            (byteCount < 8) ?

                                                // The length fits unextended, so we need 1 byte for the
                                                //  header itself, one byte for the type and "length-many"
                                                //  bytes for the value so this is the fifth case
                                                res5 :

                                                // We must extend the header byte, that is one more byte
                                                //  compared to the first case is needed which is the sixth
                                                //  and last case
                                                res6
                                        );
                        };

                        static const ResultType select_rt(const AttributeElementHeader* const header) {
                            // We have to use the element header struct here instead of the
                            //  attribute header struct since we would create circular include
                            //  dependencies otherwise

                            if (header->isHighDensity()) {
                                // High density attributes
                                if (header->lengthValueSwitch) {
                                    // Length is contained
                                    if (header->extension) {
                                        // Length fits extended
                                        return (res4);
                                    } else {
                                        // Length fits unextended
                                        return (res3);
                                    }
                                } else {
                                    // Value is contained
                                    if (header->extension) {
                                        // Value fits extended
                                        return (res2);
                                    } else {
                                        // Value fits unextended
                                        return (res1);
                                    }
                                }
                            } else {
                                // Low density attributes
                                if (header->extension) {
                                    // Length fits extended
                                    return (res6);
                                } else {
                                    // Length fits unextended
                                    return (res5);
                                }
                            }
                        }
                };

            } // end namespace detail
        } // end namespace attributes
    } // end namespace mw
} // end namespace famouso

#endif // _Case_Selector_