| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
| Cc: | pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: mcvstats serialization code is still shy of a load |
| Date: | 2019-06-26 13:40:30 |
| Message-ID: | 26130.1561556430@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On Tue, Jun 25, 2019 at 11:52:28PM -0400, Tom Lane wrote:
>> You can *not* cast something to an aligned pointer type if it's not
>> actually certain to be aligned suitably for that type.
> OK. So the solution is to ditch the casts altogether, and then do plain
> pointer arithmetics like this:
> #define ITEM_INDEXES(item) (item)
> #define ITEM_NULLS(item,ndims) (ITEM_INDEXES(item) + (ndims))
> #define ITEM_FREQUENCY(item,ndims) (ITEM_NULLS(item, ndims) + (ndims))
> #define ITEM_BASE_FREQUENCY(item,ndims) (ITEM_FREQUENCY(item, ndims) + sizeof(double))
> Or is that still relying on alignment, somehow?
No, constructs like a char* pointer plus n times sizeof(something) should
be safe.
regards, tom lane
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