什么是对齐的内存分配? [英] What is aligned memory allocation?

问题描述

我还想知道glibc malloc()是否这样做.

I also want to know whether glibc malloc() does this.

推荐答案

对齐要求指定了什么地址偏移量可以分配给什么类型.这完全取决于实现，但通常基于字长.例如，某些32位体系结构要求所有int变量均以4的倍数开头.在某些架构上，对齐要求是绝对的.对于其他对象(例如x86)，轻视它们只会导致性能下降.

Alignment requirements specify what address offsets can be assigned to what types. This is completely implementation-dependent, but is generally based on word size. For instance, some 32-bit architectures require all int variables start on a multiple of four. On some architectures, alignment requirements are absolute. On others (e.g. x86) flouting them only comes with a performance penalty.

malloc返回适合任何对齐要求的地址.换句话说，可以将返回的地址分配给任何类型的指针.根据C99§7.20.3(内存管理功能):

malloc is required to return an address suitable for any alignment requirement. In other words, the returned address can be assigned to a pointer of any type. From C99 §7.20.3 (Memory management functions):

如果分配则返回指针 成功地进行适当调整，以便 它可以分配给任何指针 对象的类型，然后用于访问 这样的对象或这样的数组 分配空间中的对象(直到 该空间已明确释放).

The pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to a pointer to any type of object and then used to access such an object or an array of such objects in the space allocated (until the space is explicitly deallocated).

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