特征实例包含另一个持有固定大小特征对象的实例 [英] Eigen instance containing another instance holding a fixed-size eigen object

问题描述

我刚刚阅读了具有静态成员的结构本征页面。后者指出以下内容：

如果定义的结构具有固定大小的可矢量化特征类型成员，则必须重载其 operator new ，以便它生成16字节对齐的指针。幸运的是，Eigen为您提供了一个宏EIGEN_MAKE_ALIGNED_OPERATOR_NEW，可以为您完成此操作。 EIGEN_MAKE_ALIGNED_OPERATOR_NEW 宏用于包含其他类实例的类实例，而其他类实例又持有固定大小的容器？

例如，在后续代码段的A类中，是否需要EIGEN_MAKE_ALIGNED_OPERATOR_NEW？

  #include< Eigen / Core> 
 
 B类
 {
 public：
 EIGEN_MAKE_ALIGNED_OPERATOR_NEW; 
 Eigen :: Vector2d v; 
}; 
 
类别A 
 {
 public：
 B b; 
}; 
 
 
 int main（int argc，char * argv []）
 {
 B * b = new B（）; //这应该没有对齐问题，因为我们使用EIGEN_MAKE_ALIGNED_OPERATOR_NEW 
 A * a = new A（）; // 这个怎么样？ 
 
返回0; 
} 
  

解决方案

在您的情况下在 A 和 B 中。如果 A 将从 B 继承，则它也将继承 new 运算符（因此不必再次编写）。另外，如果 B 本身永远不会直接分配，而只是作为 A 的一部分，则需要 EIGEN_MAKE_ALIGNED_OPERATOR_NEW 仅在 A 中使用。

此外，如果编译为在x86_64体系结构中，您的程序也很有可能会工作，因为大多数编译器将始终对 new 的结果进行16字节对齐，而只需添加 EIGEN_MAKE_ALIGNED_OPERATOR_NEW 到处都几乎不会影响性能（除非您过多地（取消）分配了对象）。

I 've just read the Structures having static members eigen page. The latter states the following:

If you define a structure having members of fixed-size vectorizable Eigen types, you must overload its "operator new" so that it generates 16-bytes-aligned pointers. Fortunately, Eigen provides you with a macro EIGEN_MAKE_ALIGNED_OPERATOR_NEW that does that for you.

However it's not clear to me whether we should also use the EIGEN_MAKE_ALIGNED_OPERATOR_NEW macro for class instances that hold other class instances which in turn hold the fixed-size containers?

For example, in class A of the followin snippet, is the EIGEN_MAKE_ALIGNED_OPERATOR_NEW needed?

#include <Eigen/Core>

class B
{
public:
  EIGEN_MAKE_ALIGNED_OPERATOR_NEW;
  Eigen::Vector2d v;
};

class A
{
public:
  B b;
};


int main(int argc, char *argv[])
{
  B* b = new B(); // this should have no alignement problems as we use EIGEN_MAKE_ALIGNED_OPERATOR_NEW
  A* a = new A(); // how about this one?

  return 0;
}

解决方案

In your case it is needed in both A and B. If A would inherit from B it would also inherit the new operator (thus making it not necessary to write again). Also, if B itself would never be allocated directly, but just as part of A, you would need the EIGEN_MAKE_ALIGNED_OPERATOR_NEW only in A.

Also, if you compile for a x86_64 architecture your program will also very likely work, since most compilers will always 16byte-align the result of new, on the other hand, just adding EIGEN_MAKE_ALIGNED_OPERATOR_NEW everywhere will barely have a performance impact (unless you excessively (de-)allocate objects).

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