InterleavedMemoryWrapper< S, V > Class Template Reference

Detailed Description

template<typename S, typename V>
class Vc::Common::InterleavedMemoryWrapper< S, V >

Wraps a pointer to memory with convenience functions to access it via vectors.

Parameters

S	The type of the struct.
V	The type of the vector to be returned when read. This should reflect the type of the members inside the struct.

See also

operator[]

Definition at line 177 of file interleavedmemory.h.

#include <Vc/Memory>

Public Member Functions
	InterleavedMemoryWrapper (S *s)
	Constructs the wrapper object. More...
template<typename IT >
enable_if< std::is_convertible< IT, IndexType >::value &&!std::is_const< S >::value, Access >	operator[] (IT indexes)
	Interleaved scatter/gather access. More...
ReadAccess	operator[] (IndexType indexes) const
	const overload (gathers only) of the above function
ReadAccess	gather (IndexType indexes) const
	alias of the above function
ReadSuccessiveEntries	operator[] (size_t first) const
	Interleaved access. More...

Constructor & Destructor Documentation

InterleavedMemoryWrapper ( S *  s )

inline

Constructs the wrapper object.

Parameters

s	A pointer to a C-array.

Definition at line 202 of file interleavedmemory.h.

Member Function Documentation

enable_if< std::is_convertible<IT, IndexType>::value && !std::is_const<S>::value, Access> operator[] ( IT  indexes )

inline

Interleaved scatter/gather access.

Assuming you have a struct of floats and a vector of indexes into the array, this function can be used to access the struct entries as vectors using the minimal number of store or load instructions.

Parameters

indexes

Vector of indexes that determine the gather locations.

Returns

A special (magic) object that executes the loads and deinterleave on assignment to a vector tuple.

Example:

struct Foo {
  float x, y, z;
};

void fillWithBar(Foo *_data, uint_v indexes)
{
  Vc::InterleavedMemoryWrapper<Foo, float_v> data(_data);
  const float_v x = bar(1);
  const float_v y = bar(2);
  const float_v z = bar(3);
  data[indexes] = (x, y, z);
  // it's also possible to just store a subset at the front of the struct:
  data[indexes] = (x, y);
  // if you want to store a single entry, use scatter:
  z.scatter(_data, &Foo::x, indexes);
}

float_v normalizeStuff(Foo *_data, uint_v indexes)
{
  Vc::InterleavedMemoryWrapper<Foo, float_v> data(_data);
  float_v x, y, z;
  (x, y, z) = data[indexes];
  // it is also possible to just load a subset from the front of the struct:
  // (x, y) = data[indexes];
  return Vc::sqrt(x * x + y * y + z * z);
}

You may think of the gather operation (or scatter as the inverse) like this:

             Memory: {x0 y0 z0 x1 y1 z1 x2 y2 z2 x3 y3 z3 x4 y4 z4 x5 y5 z5 x6 y6 z6 x7 y7 z7 x8 y8 z8}
            indexes: [5, 0, 1, 7]
Result in (x, y, z): ({x5 x0 x1 x7}, {y5 y0 y1 y7}, {z5 z0 z1 z7})

   \warning If \p indexes contains non-unique entries on scatter, the result is undefined. If
   \c NDEBUG is not defined the implementation will assert that the \p indexes entries are unique.

Definition at line 262 of file interleavedmemory.h.

ReadSuccessiveEntries operator[] ( size_t  first ) const

inline

Interleaved access.

This function is an optimization of the function above, for cases where the index vector contains consecutive values. It will load V::Size consecutive entries from memory and deinterleave them into Vc vectors.

Parameters

first

The first of V::Size indizes to be accessed.

Returns

A special (magic) object that executes the loads and deinterleave on assignment to a vector tuple.

Example:

struct Foo {
  float x, y, z;
};

void foo(Foo *_data)
{
  Vc::InterleavedMemoryWrapper<Foo, float_v> data(_data);
  for (size_t i = 0; i < 32U; i += float_v::Size) {
    float_v x, y, z;
    (x, y, z) = data[i];
    // now:
    // x = { _data[i].x, _data[i + 1].x, _data[i + 2].x, ... }
    // y = { _data[i].y, _data[i + 1].y, _data[i + 2].y, ... }
    // z = { _data[i].z, _data[i + 1].z, _data[i + 2].z, ... }
    ...
  }
}

Definition at line 309 of file interleavedmemory.h.

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The documentation for this class was generated from the following file:

• /u/mkretz/src/.Vc-dox/common/interleavedmemory.h