Memory< V, Size, 0u > Class Template Reference

Detailed Description

template<typename V, size_t Size>
class Vc::Memory< V, Size, 0u >

A helper class to simplify usage of correctly aligned and padded memory, allowing both vector and scalar access.

Example:

Vc::Memory<int_v, 11> array;

// scalar access:
for (size_t i = 0; i < array.entriesCount(); ++i) {
    int x = array[i]; // read
    array[i] = x;     // write
}
// more explicit alternative:
for (size_t i = 0; i < array.entriesCount(); ++i) {
    int x = array.scalar(i); // read
    array.scalar(i) = x;     // write
}

// vector access:
for (size_t i = 0; i < array.vectorsCount(); ++i) {
    int_v x = array.vector(i); // read
    array.vector(i) = x;       // write
}

This code allocates a small array and implements three equivalent loops (that do nothing useful). The loops show how scalar and vector read/write access is best implemented.

Since the size of 11 is not a multiple of int_v::Size (unless you use the scalar Vc implementation) the last write access of the vector loop would normally be out of bounds. But the Memory class automatically pads the memory such that the whole array can be accessed with correctly aligned memory addresses.

Parameters

V	The vector type you want to operate on. (e.g. float_v or uint_v)
Size	The number of entries of the scalar base type the memory should hold. This is thus the same number as you would use for a normal C array (e.g. float mem[11] becomes Memory<float_v, 11> mem).

See Also

Memory<V, 0u>

#include <Vc/Memory>

Inherits VectorAlignedBaseT< V >, and MemoryBase< V, Memory< V, Size, 0u >, 1, void >.

Public Member Functions
constexpr size_t	entriesCount () const
constexpr 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.
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, A >	vectorAt (size_t i, A align=Vc::Aligned)
const VectorPointerHelperConst < V, A >	vectorAt (size_t i, A align=Vc::Aligned) 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.

Static Public Member Functions
static Memory< V, Size, 0u > &	fromRawData (EntryType *ptr)
	Wrap existing data with the Memory convenience class.

Member Function Documentation

static Memory<V, Size, 0u>& fromRawData ( EntryType *  ptr )

static

Wrap existing data with the Memory convenience class.

This function returns a reference to a Memory<V, Size, 0> object that you must capture to avoid a copy of the whole data:

Memory<float_v, 16> &m = Memory<float_v, 16>::fromRawData(someAlignedPointerToFloat)

Parameters

ptr	An aligned pointer to memory of type V::EntryType (e.g. float for Vc::float_v).

Returns

A Memory object placed at the given location in memory.

Warning

The pointer ptr passed to this function must be aligned according to the alignment restrictions of V.

The size of the accessible memory must match Size. This includes the required padding at the end to allow the last entries to be accessed via vectors. If you know what you are doing you might violate this constraint.

It is your responsibility to ensure that the memory is released correctly (not too early/not leaked). This function simply adds convenience functions to access the memory.

constexpr size_t entriesCount

(

)

const

Returns

the number of scalar entries in the whole array.

Note

This function can be optimized into a compile-time constant.

Reimplemented from MemoryBase< V, Memory< V, Size, 0u >, 1, void >.

constexpr size_t vectorsCount

(

)

const

Returns

the number of vectors in the whole array.

Note

This function can be optimized into a compile-time constant.

Reimplemented from MemoryBase< V, Memory< V, Size, 0u >, 1, void >.

VectorPointerHelper<V, AlignedFlag> vector ( size_t  i )

inherited

Parameters

i	Selects 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

inherited

Const overload of the above function.

Parameters

i	Selects the offset, where the vector should be read.

Returns

a smart object to wrap the i-th vector in the memory.

VectorPointerHelper<V, UnalignedFlag> vector ( size_t  i, int  shift  )

inherited

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

i	Selects 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]).
shift	Shifts 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, A> vectorAt ( size_t  i, A  align = Vc::Aligned  )

inherited

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

i	Specifies 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.
align	You 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, A  align = Vc::Aligned  ) const

inherited

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

i	Specifies 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.
align	You 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, AlignedFlag> firstVector ( )

inherited

Returns

the first vector in the allocated memory.

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

VectorPointerHelper<V, AlignedFlag> lastVector ( )

inherited

Returns

the last vector in the allocated memory.

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