Vc  0.7.5-dev
SIMD Vector Classes for C++
MemoryBase< V, Parent, Dimension, RowMemory > Class Template Reference

Detailed Description

template<typename V, typename Parent, int Dimension, typename RowMemory>
class Vc::MemoryBase< V, Parent, Dimension, RowMemory >

Common interface to all Memory classes, independent of allocation on the stack or heap.

Parameters
VThe vector type you want to operate on. (e.g. float_v or uint_v)
ParentThis type is the complete type of the class that derives from MemoryBase.
DimensionThe number of dimensions the implementation provides.
RowMemoryClass to be used to work on a single row.

#include <Vc/Memory>

Inherits MemoryDimensionBase< V, Parent, Dimension, RowMemory >.

Public Types

typedef V::EntryType EntryType
 The type of the scalar entries in the array.

Public Member Functions

size_t entriesCount () const
size_t vectorsCount () const
VectorPointerHelper< V,
AlignedFlag > 
vector (size_t i)
const VectorPointerHelperConst
< V, AlignedFlag > 
vector (size_t i) const
 Const overload of the above function.
template<typename A >
VectorPointerHelper< V, A > vectorAt (size_t i, A align=Vc::Aligned)
template<typename A >
const VectorPointerHelperConst
< V, A > 
vectorAt (size_t i, A align=Vc::Aligned) const
 Const overload of the above function.
VectorPointerHelper< V,
UnalignedFlag > 
vector (size_t i, int shift)
const VectorPointerHelperConst
< V, UnalignedFlag > 
vector (size_t i, int shift) const
 Const overload of the above function.
VectorPointerHelper< V,
AlignedFlag > 
firstVector ()
const VectorPointerHelperConst
< V, AlignedFlag > 
firstVector () const
 Const overload of the above function.
VectorPointerHelper< V,
AlignedFlag > 
lastVector ()
const VectorPointerHelperConst
< V, AlignedFlag > 
lastVector () const
 Const overload of the above function.

Member Function Documentation

size_t entriesCount ( ) const
Returns
the number of scalar entries in the array. This function is optimized away if a constant size array is used.

Reimplemented in Memory< V, 0u, 0u >, Memory< V, Size, 0u >, and Memory< V, Size1, Size2 >.

size_t vectorsCount ( ) const
Returns
the number of vector entries that span the array. This function is optimized away if a constant size array is used.

Reimplemented in Memory< V, 0u, 0u >, Memory< V, Size, 0u >, and Memory< V, Size1, Size2 >.

VectorPointerHelper<V, AlignedFlag> vector ( size_t  i)
Parameters
iSelects the offset, where the vector should be read.
Returns
a smart object to wrap the i-th vector in the memory.

The return value can be used as any other vector object. I.e. you can substitute something like

float_v a = ..., b = ...;
a += b;

with

mem.vector(i) += b;

This function ensures that only aligned loads and stores are used. Thus it only allows to access memory at fixed strides. If access to known offsets from the aligned vectors is needed the vector(size_t, int) function can be used.

const VectorPointerHelperConst<V, AlignedFlag> vector ( size_t  i) const

Const overload of the above function.

Parameters
iSelects the offset, where the vector should be read.
Returns
a smart object to wrap the i-th vector in the memory.
VectorPointerHelper<V, A> vectorAt ( size_t  i,
align = Vc::Aligned 
)
Returns
a smart object to wrap the vector starting from the i-th scalar entry in the memory.

Example:

Memory<float_v, N> mem;
mem.setZero();
for (int i = 0; i < mem.entriesCount(); i += float_v::Size) {
mem.vectorAt(i) += b;
}
Parameters
iSpecifies the scalar entry from where the vector will be loaded/stored. I.e. the values scalar(i), scalar(i + 1), ..., scalar(i + V::Size - 1) will be read/overwritten.
alignYou must take care to determine whether an unaligned load/store is required. Per default an aligned load/store is used. If i is not a multiple of V::Size you must pass Vc::Unaligned here.
const VectorPointerHelperConst<V, A> vectorAt ( size_t  i,
align = Vc::Aligned 
) const

Const overload of the above function.

Returns
a smart object to wrap the vector starting from the i-th scalar entry in the memory.
Parameters
iSpecifies the scalar entry from where the vector will be loaded/stored. I.e. the values scalar(i), scalar(i + 1), ..., scalar(i + V::Size - 1) will be read/overwritten.
alignYou must take care to determine whether an unaligned load/store is required. Per default an aligned load/store is used. If i is not a multiple of V::Size you must pass Vc::Unaligned here.
VectorPointerHelper<V, UnalignedFlag> vector ( size_t  i,
int  shift 
)
Returns
a smart object to wrap the i-th vector + shift in the memory.

This function ensures that only unaligned loads and stores are used. It allows to access memory at any location aligned to the entry type.

Parameters
iSelects the memory location of the i-th vector. Thus if V::Size == 4 and i is set to 3 the base address for the load/store will be the 12th entry (same as &mem[12]).
shiftShifts the base address determined by parameter i by shift many entries. Thus vector(3, 1) for V::Size == 4 will load/store the 13th - 16th entries (same as &mem[13]).
Note
Any shift value is allowed as long as you make sure it stays within bounds of the allocated memory. Shift values that are a multiple of V::Size will not result in aligned loads. You have to use the above vector(size_t) function for aligned loads instead.
Thus a simple way to access vectors randomly is to set i to 0 and use shift as the parameter to select the memory address:
// don't use:
mem.vector(i / V::Size, i % V::Size) += 1;
// instead use:
mem.vector(0, i) += 1;
VectorPointerHelper<V, AlignedFlag> firstVector ( )
Returns
the first vector in the allocated memory.

This function is simply a shorthand for vector(0).

VectorPointerHelper<V, AlignedFlag> lastVector ( )
Returns
the last vector in the allocated memory.

This function is simply a shorthand for vector(vectorsCount() - 1).