Re: standard memory allocator alignment issue...

"Chris Thomasson" <cristom@[EMAIL PROTECTED]
> writes:

> "Ben Bacarisse" <ben.usenet@[EMAIL PROTECTED]
> wrote in message
> news:877idz81nm.fsf@[EMAIL PROTECTED]
>
> [...]
>> The suggestion seems to be that ALIGN_MAX is some arithmetic value.  I
>> can't see a way to adjust a pointer using it in any po[r]table way.
<snip, but permit me to correct my typo!>
>
> I am currently using something like the following hack to align
> pointers on boundaries which are powers of 2:
<snip>
> typedef long int align_detail_intptr;
<snip>
> #define ALIGN_POW2(mp_this, mp_type) ((mp_type)( \
>  (((align_detail_intptr const)(mp_this)) + 1) & (-2) \
> ))
>
>
> #define ALIGN(mp_this, mp_type, mp_align) ((mp_type)( \
>  (((align_detail_intptr const)(mp_this)) + \
>   ALIGN_POW2(mp_align, align_detail_intptr const) - 1) \
>  & (-ALIGN_POW2(mp_align, align_detail_intptr const)) \
> ))
<snip>
> Any suggestions on how to improve the abomination?
>
> ;^)

I would do***ent (maybe another clause in your static assert?) that
long must be able to hold a pointer (I assume you can't use C99's
intptr_t?).

You rely on the representation of -2 and of -ALIGN_POW2(...).  I'd use
all unsigned types to avoid both.  Other than that, I think this is
the best you can do (but I am no expert on this so you may well get
better advice shortly...).

-- 
Ben.