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 /*  This file is part of the Vc library. {{{
 Copyright © 2014-2015 Matthias Kretz <kretz@kde.org>
 
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     * 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
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       documentation and/or other materials provided with the distribution.
     * Neither the names of contributing organizations nor the
       names of its 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 HOLDER BE LIABLE FOR ANY
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 }}}*/
 
 #ifndef Vc_CURRENT_CLASS_NAME
 #error "incorrect use of common/gatherinterface.h: Vc_CURRENT_CLASS_NAME must be defined to the current class name for declaring constructors."
 #endif
 
 ///////////////////////////////////////////////////////////////////////////////////////////
 // gathers
 // A gather takes the following arguments:
 // 1. A const pointer to memory of any type that can convert to EntryType
 // 2. An indexes “vector”. The requirement is that the type implements the subscript operator,
 //    stores «Size» valid index values, and each offset to the pointer above yields a valid
 //    memory location for reading.
 // 3. Optionally the third argument may be a mask. The mask disables several memory reads and
 //    thus removes the requirements in (2.) for the disabled entries.
 
 private:
     /**\internal
      * This function implements a gather given a pointer to memory \p mem and some
      * container object storing the gather \p indexes.
      *
      * \param mem This pointer must be aligned correctly for the type \p MT. This is the
      * natural behavior of C++, so this is typically the case.
      * \param indexes This object contains at least \VSize{T} indexes that denote the
      * offset in \p mem where the components for the current vector should be copied from.
      * The offset is not in Bytes, but in multiples of `sizeof(MT)`.
      */
     // enable_if<std::can_convert<MT, EntryType>::value &&
     // has_subscript_operator<IT>::value>
     template <class MT, class IT, int Scale = 1>
     inline void gatherImplementation(const Common::GatherArguments<MT, IT, Scale> &);
 
     /**\internal
      * This overload of the above function adds a \p mask argument to disable memory
      * accesses at the \p indexes offsets where \p mask is \c false.
      */
     template <class MT, class IT, int Scale = 1>
     inline void gatherImplementation(const Common::GatherArguments<MT, IT, Scale> &,
                                      MaskArgument mask);
 
 public:
 #define Vc_ASSERT_GATHER_PARAMETER_TYPES_                                                \
     static_assert(                                                                       \
         std::is_convertible<MT, EntryType>::value,                                       \
         "The memory pointer needs to point to a type that can be converted to the "      \
         "EntryType of this SIMD vector type.");                                          \
     static_assert(                                                                       \
         Vc::Traits::has_subscript_operator<IT>::value,                                   \
         "The indexes argument must be a type that implements the subscript operator.");  \
     static_assert(                                                                       \
         !Traits::is_simd_vector<IT>::value ||                                            \
             Traits::simd_vector_size<IT>::value >= Size,                                 \
         "If you use a SIMD vector for the indexes parameter, the index vector must "     \
         "have at least as many entries as this SIMD vector.");                           \
     static_assert(                                                                       \
         !std::is_array<T>::value ||                                                      \
             (std::rank<T>::value == 1 &&                                                 \
              (std::extent<T>::value == 0 || std::extent<T>::value >= Size)),             \
         "If you use a simple array for the indexes parameter, the array must have "      \
         "at least as many entries as this SIMD vector.")
 
     /**
      * \name Gather constructors and member functions
      *
      * Constructs or loads a vector from the objects at `mem[indexes[0]]`,
      * `mem[indexes[1]]`, `mem[indexes[2]]`, ...
      *
      * All gather functions optionally take a mask as last argument. In that case only the
      * entries that are selected in the mask are accessed in memory and copied to the
      * vector. This enables invalid indexes in the \p indexes vector if those are masked
      * off in \p mask.
      *
      * Gathers from structured data (AoS: arrays of struct) are possible via a special
      * subscript operator of the container (array). You can use \ref Vc::array and \ref
      * Vc::vector as drop-in replacements for \c std::array and \c std::vector. These
      * container classes contain the necessary subscript operator overload. Example:
      * \code
      * Vc::vector<float> data(100);
      * std::iota(data.begin(), data.end(), 0.f);  // fill with values 0, 1, 2, ...
      * auto indexes = float_v::IndexType::IndexesFromZero();
      * float_v gathered = data[indexes];  // gathered == [0, 1, 2, ...]
      * \endcode
      *
      * This also works for gathers into arrays of structures:
      * \code
      * struct Point { float x, y, z; };
      * Vc::array<Point, 100> points;
      * // fill points ...
      * auto indexes = float_v::IndexType::IndexesFromZero();
      * float_v xs = data[indexes][&Point::x];  // [points[0].x, points[1].x, points[2].x, ...]
      * float_v ys = data[indexes][&Point::y];  // [points[0].y, points[1].y, points[2].y, ...]
      * float_v zs = data[indexes][&Point::z];  // [points[0].z, points[1].z, points[2].z, ...]
      * \endcode
      *
      * Alternatively, you can use Vc::Common::AdaptSubscriptOperator to extend a given
      * container class with the necessary subscript operator. Example:
      * \code
      * template <typename T, typename Allocator = std::allocator<T>>
      * using my_vector = Vc::Common::AdaptSubscriptOperator<std::vector<T, Allocator>>;
      * \endcode
      *
      * \param mem A pointer to memory which contains objects of type \p MT at the offsets
      *            given by \p indexes.
      * \param indexes A container/vector of offsets into \p mem.
      *                The type of \p indexes (\p IT) may either be a pointer to integers
      *                (C-array) or a vector of integers (preferrably IndexType).
      * \param mask If a mask is given, only the active entries will be copied from memory.
      *
      * \note If you use a masked gather constructor the masked-off entries of the vector
      * are zero-initilized.
      */
     ///@{
 
     /// Gather constructor
     template <typename MT, typename IT,
               typename = enable_if<Traits::has_subscript_operator<IT>::value>>
     Vc_INTRINSIC Vc_CURRENT_CLASS_NAME(const MT *mem, const IT &indexes)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(
             Common::make_gather<1>(mem, Common::convertIndexVector(indexes)));
     }
 
     template <class MT, class IT, int Scale>
     Vc_INTRINSIC Vc_CURRENT_CLASS_NAME(const Common::GatherArguments<MT, IT, Scale> &args)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(args);
     }
 
     /// Masked gather constructor
     template <typename MT, typename IT,
               typename = enable_if<Vc::Traits::has_subscript_operator<IT>::value>>
     Vc_INTRINSIC Vc_CURRENT_CLASS_NAME(const MT *mem, const IT &indexes,
                                        MaskArgument mask)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(
             Common::make_gather<1>(mem, Common::convertIndexVector(indexes)), mask);
     }
 
     template <class MT, class IT, int Scale>
     Vc_INTRINSIC Vc_CURRENT_CLASS_NAME(const Common::GatherArguments<MT, IT, Scale> &args,
                                        MaskArgument mask)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(args, mask);
     }
 
     /// Gather function
     template <typename MT, typename IT,
               typename = enable_if<Vc::Traits::has_subscript_operator<IT>::value>>
     Vc_INTRINSIC void gather(const MT *mem, const IT &indexes)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(
             Common::make_gather<1>(mem, Common::convertIndexVector(indexes)));
     }
 
     /// Masked gather function
     template <typename MT, typename IT,
               typename = enable_if<Vc::Traits::has_subscript_operator<IT>::value>>
     Vc_INTRINSIC void gather(const MT *mem, const IT &indexes, MaskArgument mask)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(
             Common::make_gather<1>(mem, Common::convertIndexVector(indexes)), mask);
     }
     ///@}
 
 #include "gatherinterface_deprecated.h"
 
     /**\internal
      * \name Gather function to use from Vc::Common::subscript_operator
      *
      * \param args
      * \param mask
      */
     ///@{
     template <class MT, class IT, int Scale>
     Vc_INTRINSIC void gather(const Common::GatherArguments<MT, IT, Scale> &args)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(args);
     }
 
     template <class MT, class IT, int Scale>
     Vc_INTRINSIC void gather(const Common::GatherArguments<MT, IT, Scale> &args,
                              MaskArgument mask)
     {
         Vc_ASSERT_GATHER_PARAMETER_TYPES_;
         gatherImplementation(args, mask);
     }
     ///@}
 
 #undef Vc_ASSERT_GATHER_PARAMETER_TYPES_

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