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Re: new module 'aligned-malloc'


From: Bruno Haible
Subject: Re: new module 'aligned-malloc'
Date: Wed, 22 Jul 2020 01:29:24 +0200
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Paul Eggert wrote:
> I don't see why not, at least on platforms of interest to Gnulib. On systems 
> that provide no native way to do an aligned allocation, we merely keep 
> calling 
> malloc with suitable arguments until we get a pointer that is suitably 
> aligned. 
> We then free all the unsuitable storage we allocated along the way, and 
> return 
> the good pointer.
> 
> Of course this would not be as efficient as a native aligned_alloc would be, 
> but 
> it should be good enough for portability to nonstandard platforms, for many 
> applications anyway - and that is the Gnulib Way.

Well, the Gnulib way is to accept some small penalty for nonstandard platforms.
However, the algorithm above would be _grossly_ inefficient - especially for
bigger alignments such as 128 or 512. I don't wish to penalize the runtime
behaviour of any GNU program like this.

> There is a real advantage to using aligned_alloc instead of some nonstandard 
> allocate/free pair. With aligned_alloc you can hand pointers off to other 
> code 
> that expects to use 'free' (and there is a lot of such code out there).

It depends on the programs. In a lot of code I've seen, allocation and
deallocation of some data type is done nearby in the code; then it's not
a big burden to use xyz_free for the results of xyz_alloc.

Bruno




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