Storable tuples and what is 'alignment'?
glynn.clements at virgin.net
Tue Aug 6 13:58:28 EDT 2002
Simon Marlow wrote:
> > You also need to allow for any padding which is required to satisfy
> > the alignment constraints of b, e.g.
> > sizeOf (a,b) = sizeOf a + padding (a,b) + sizeOf b
> > where padding (a,b) = (alignment b - sizeOf a
> > `mod` alignment b) `mod` alignment b
> > > alignment (a,b) = alignment a + alignment b
> > The alignment of the overall structure is determined by the alignment
> > of the first element. Subsequent elements are aligned (if necessary)
> > by the addition of padding between elements.
> > alignment (a,_) = alignment a
... except, of course, that you would then need a variable amount of
padding if b's alignment exceeds that of a.
> I think in fact that the aligment of the whole structure should be
> alignment (a,b) = alignment a `max` aligment b
Technically, it should be the least common multiple of the components'
alignments. If alignments were guaranteed to be a power of two (as
they invariably are), then "max" would suffice; but I can't find
anything in the documentation which actually *states* that that is the
Glynn Clements <glynn.clements at virgin.net>
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