In scientific computing, the most common problem is to have a very large number of structures instead of a single one.
The definition of a structure that represents a single object is not the best abstraction, as it has negative consequences on the memory layout.
Although it can lead to more “surface” complexity, treating a collection of objects as the fundamental entity in the code is a more sensible abstraction, that leads to what is known as Data-Oriented design.
See main.cpp for an example how to use the classes (especially for *The AoSoAElement class).
C++11 is required to compile the code. It is possible to make the code C++03 compliant at the cost of more verbosity.
To compile and run the example, simply:
$g++ -o main main.cpp && ./mainThe AoSoA class takes care only
of abstracting the memory layout
of a collection of homogeneous structures
(that is, where all data members have the same type).
Its constructor takes an already allocated pointer (single responsitiliby principle). The allocated memory is subject to some limitations: see *Limitations.
The data is accessed using two indices,
an index idx to select the structure
and another internal index icomponent to select the component.
For example, if the array needs to contain
complex double precision spinors in a gauge theory with N = 3,
on an machine where the SIMD vector length is 512 bits,
there will be 512/128 = 4 element per SIMD vector,
and we will have 0 <= icomponent < 12.
The indexing inside the structure is left to any other class (single responsibility principle).
The size of the memory allocated needs to be a multiple of the size of the base object times the lenght of the vector.
In the example mentioned above,
the memory allocated needs to be a multiple of (12*64) bytes,
where 12 is the number of components in the object,
and 64 is the size of the vector in bytes.
A convenient lazy class that represents a reference to single object in a container.
This class is not necessary, but it is provided in the hope that it is useful.
It is a wrapper around an index idx
and a reference to an AoSoA array.
Such objects can be created using operator []
from the AoSoA class.
The AoSoAElement class
also overloads operator [],
which returns a reference to a component.
For a copy of/const reference to a component, use operator() instead.
It provides element-by-element operations
like assignment, +=, *= and the like.