对齐的malloc和标准malloc之间的区别? [英] Difference between aligned malloc and standard malloc?

问题描述

我是malloc和对齐malloc的新手.我知道如何使用它们.但是，我不确切知道在那种情况下我们应该使用对齐的malloc而不是标准的malloc.你能给我解释一下吗?

I'm new to malloc and aligned malloc. I know how to use them. However, I don't know exactly in which case we should use aligned malloc instead of standard malloc. Can you explain it to me please?

推荐答案

glibc文档相当清楚地表明您应该在哪里使用aligned_alloc:

在GNU系统中，由malloc或realloc返回的块的地址始终为8的倍数(在64位系统上为16).如果您需要一个块的地址是其高2的幂的倍数，请使用aligned_alloc或posix_memalign.

The address of a block returned by malloc or realloc in GNU systems is always a multiple of eight (or sixteen on 64-bit systems). If you need a block whose address is a multiple of a higher power of two than that, use aligned_alloc or posix_memalign.

C标准已经保证malloc将为任何标准类型返回适当对齐的内存块，但是在某些情况下，您可能需要或需要更严格的对齐方式.

The C standard already guarantees that malloc will return a suitably aligned memory block for any of the standard types but there may be situations in which you want or need stricter alignment.

作为一个例子，我似乎想起了SSE2(SIMD)指令需要将其数据对齐在16个字节的边界上，因此即使在malloc仅保证与8对齐的系统上，您也可以使用aligned_alloc为您提供数据字节边界.

As one example, I seem to recall that SSE2 (SIMD) instructions need their data aligned on 16-byte boundaries so you could use aligned_alloc to give you that even on systems where malloc only guarantees alignment to an 8-byte boundary.

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