Re: [boost] [align] Review - Impl Evaluation Part 1.

Glen Fernandes writes:

On Sat, Apr 12, 2014 at 1:11 PM, Mostafa

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Unfortunately I don't understand what you're trying to say. Additionally let me rephrase my question, why is it that in the absence of a platform-specific aligned_alloc the boost provided aligned_alloc silently aligns on alignof(void *) if the user requested alignment value is less

yahoo.com> wrote: than

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alignof(void *)? (I understand this is still correct behaviour, just curious since the boost provided aligned_alloc uses boost::align to align the memory buffer and, per your previous response, "An alignment smaller than alignof(void*) is still a valid fundamental alignment, so align() should be usable with such values.")

Ah, I had misinterpreted your question. The reason why the Boost-provided aligned_alloc will ensure alignment is a minimum of alignof(void*), is because after calling align(), we want to access the sizeof(void*) bytes immediately preceding the aligned memory as a void*, so that address must be suitably aligned for void*.

Instead of *(static_cast(p1) - 1) = p2; I could have used std::memcpy to copy p2 into that storage, and then it would not require that storage to be at-least alignof(void*) aligned.

Thanks for the explanation. Then I think the documentation for aligned_alloc needs to be updated from: "... by an additional sizeof(void*) and alignment bytes." to: "... by an additional sizeof(void*) and max(alignment, sizeof(void *)) bytes." to take into account the silent alignment bumping that may occur in some scenarios.