Developer Guide and Reference

  • 2022.1
  • 04/11/2022
  • Public Content
Contents

struct dnnl::memory::desc

Overview

A memory descriptor. More…
#include <dnnl.hpp> struct desc { // fields dnnl_memory_desc_t data; // construction desc(); desc( const dims& adims, data_type adata_type, format_tag aformat_tag, bool allow_empty = false ); desc( const dims& adims, data_type adata_type, const dims& strides, bool allow_empty = false ); desc(const dnnl_memory_desc_t& data); // methods desc submemory_desc( const dims& adims, const dims& offsets, bool allow_empty = false ) const; desc reshape(const dims& adims, bool allow_empty = false) const; desc permute_axes(const std::vector<int>& permutation, bool allow_empty = false) const; memory::data_type data_type() const; memory::dims dims() const; size_t get_size() const; bool is_zero() const; bool operator == (const desc& other) const; bool operator != (const desc& other) const; operator bool () const; };

Detailed Documentation

A memory descriptor.
Fields
The underlying C API data structure.
Construction
desc()
Constructs a zero (empty) memory descriptor.
Such a memory descriptor can be used to indicate absence of an argument.
desc( const dims& adims, data_type adata_type, format_tag aformat_tag, bool allow_empty = false )
Constructs a memory descriptor.
The logical order of dimensions corresponds to the
abc...
format tag, and the physical meaning of the dimensions depends both on the primitive that would operate on this memory and the operation context.
Parameters:
adims
Tensor dimensions.
adata_type
Data precision/type.
aformat_tag
Memory format tag.
allow_empty
A flag signifying whether construction is allowed to fail without throwing an exception. In this case a zero memory descriptor will be constructed. This flag is optional and defaults to false.
desc( const dims& adims, data_type adata_type, const dims& strides, bool allow_empty = false )
Constructs a memory descriptor by strides.
The logical order of dimensions corresponds to the
abc...
format tag, and the physical meaning of the dimensions depends both on the primitive that would operate on this memory and the operation context.
Parameters:
adims
Tensor dimensions.
adata_type
Data precision/type.
strides
Strides for each dimension.
allow_empty
A flag signifying whether construction is allowed to fail without throwing an exception. In this case a zero memory descriptor will be constructed. This flag is optional and defaults to false.
desc(const dnnl_memory_desc_t& data)
Constructs a memory descriptor from a C API data structure.
Parameters:
data
A C API dnnl_memory_desc_t structure.
Methods
desc submemory_desc( const dims& adims, const dims& offsets, bool allow_empty = false ) const
Constructs a memory descriptor for a region inside an area described by this memory descriptor.
Parameters:
adims
Sizes of the region.
offsets
Offsets to the region from the encompassing memory object in each dimension.
allow_empty
A flag signifying whether construction is allowed to fail without throwing an exception. In this case a zero memory descriptor will be returned. This flag is optional and defaults to false.
Returns:
A memory descriptor for the region.
desc reshape(const dims& adims, bool allow_empty = false) const
Constructs a memory descriptor by reshaping an existing one.
The new memory descriptor inherits the data type. This operation is valid only for memory descriptors that have format_kind set to dnnl::memory::format_kind::blocked or dnnl::memory::format_kind::any.
The operation ensures that the transformation of the physical memory format corresponds to the transformation of the logical dimensions. If such transformation is impossible, the function either throws an exception (default) or returns a zero memory descriptor depending on the
allow_empty
flag.
The reshape operation can be described as a combination of the following basic operations:
  1. Add a dimension of size
    1
    . This is always possible.
  2. Remove a dimension of size
    1
    . This is possible only if the dimension has no padding (i.e.
    padded_dims[dim] == dims[dim] && dims[dim] == 1
    ).
  3. Split a dimension into multiple ones. This is possible only if the product of all tensor dimensions stays constant and the dimension being split does not have padding (i.e.
    padded_dims[dim] = dims[dim]
    ).
  4. Join multiple consecutive dimensions into a single one. As in the cases above, this requires that the dimensions do not have padding and that the memory format is such that in physical memory these dimensions are dense and have the same order as their logical counterparts. This also assumes that these dimensions are not blocked.
    • Here, ‘dense’ means:
      stride for dim[i] == (stride for dim[i + 1]) * dim[i + 1]
      ;
    • And ‘same order’ means:
      i < j
      if and only if
      stride for dim[j] <= stride for dim[i]
      .
Some combinations of physical memory layout and/or offsets or dimensions may result in a failure to make a reshape.
Parameters:
adims
New dimensions. The product of dimensions must remain constant.
allow_empty
A flag signifying whether construction is allowed to fail without throwing an exception. In this case a zero memory descriptor will be returned. This flag is optional and defaults to false.
Returns:
A new memory descriptor with new dimensions.
desc permute_axes(const std::vector<int>& permutation, bool allow_empty = false) const
Constructs a memory descriptor by permuting axes in an existing one.
The physical memory layout representation is adjusted accordingly to maintain the consistency between the logical and physical parts of the memory descriptor. The new memory descriptor inherits the data type.
The new memory descriptor inherits the data type. This operation is valid only for memory descriptors that have format_kind set to dnnl::memory::format_kind::blocked or dnnl::memory::format_kind::any.
The logical axes will be permuted in the following manner:
for (i = 0; i < ndims(); i++) new_desc.dims()[permutation[i]] = dims()[i];
Example:
std::vector<int> permutation = {1, 0}; // swap the first and // the second axes dnnl::memory::desc in_md( {2, 3}, data_type, memory::format_tag::ab); dnnl::memory::desc expect_out_md( {3, 2}, data_type, memory::format_tag::ba); assert(in_md.permute_axes(permutation) == expect_out_md);
Parameters:
permutation
Axes permutation.
allow_empty
A flag signifying whether construction is allowed to fail without throwing an exception. In this case a zero memory descriptor will be returned. This flag is optional and defaults to false.
Returns:
A new memory descriptor with new dimensions.
memory::data_type data_type() const
Returns the data type of the memory descriptor.
Returns:
The data type.
memory::dims dims() const
Returns dimensions of the memory descriptor.
Potentially expensive due to the data copy involved.
Returns:
A copy of the dimensions vector.
size_t get_size() const
Returns size of the memory descriptor in bytes.
Returns:
The number of bytes required to allocate a memory buffer for the memory object described by this memory descriptor including the padding area.
bool is_zero() const
Checks whether the memory descriptor is zero (empty).
Returns:
true
if the memory descriptor describes an empty memory and
false
otherwise.
bool operator == (const desc& other) const
An equality operator.
Parameters:
other
Another memory descriptor.
Returns:
Whether this and the other memory descriptors have the same format tag, dimensions, strides, blocking, etc.
bool operator != (const desc& other) const
An inequality operator.
Parameters:
other
Another memory descriptor.
Returns:
Whether this and the other memory descriptors describe different memory.
operator bool () const
Checks whether the object is not empty.
Returns:
Whether the object is not empty.

Product and Performance Information

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