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From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: Allocators design flaw
Date: Sun, 15 Oct 2017 00:26:28 +0300
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Date: 2017-10-15T00:26:28+03:00
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Simon Wright wrote:

> Victor Porton <porton@narod.ru> writes:
> 
>> There is nothing in Ada standard to prevent the above "new" operator
>> to request 256-byte alignment of the data. (Yes, I know this does not
>> happen in practice, but it is not forbidden by the RM.)
>>
>> If it requests such a great alignment by the C function
>> *_alloc_memory() is able to do only 16-byte alignment, then my
>> allocator would break the contract, that is allocate with lesser
>> alignment than requested.
> 
> Since you agree it's very unlikely that an Ada compiler would actually
> do that, why not just check the requested alignment & raise PE if it's
> too large?

I already considered this, but:

It does not seem absolutely impossible that Ada never requests alignment 
above the minimum alignment for allocated C structs. (And all we can know 
about the allocator in the C library is that it is appropriate for structs.)

For example 4 bytes seems a possible alignment for C structs, but I can't be 
completely sure that Ada never requests 8 bytes alignment.

Yes, this is unlikely, but not entirely impossible.

So I have rewritten my code without using allocators at all.

-- 
Victor Porton - http://portonvictor.org