How large are arbitrarily large integers? (Was Re: Bitfield subtlety)

[Richard Biener]

On Thu, 29 Mar 2018, Niels Möller wrote:

> Richard Biener <rguenther at suse.de> writes:
> 
> > I would be surprised if that wouldn't work everywhere - any reason
> > you have doubts?  To clarify, allocation would work like
> >
> >  void *ptr = malloc (... + sizeof (size_t));
> >  ->_mp_d = (char *)ptr + sizeof (size_t);
> >  size_t *size = ptr;
> 
> That would give bad alignment in the case that limbs are 64 bits but
> size_t only 32 bits (and the x86_64 "x32" abi is something like that,
> right?).

Yes.  Make it

  ->_mp_d = (char *)ptr + MAX(sizeof (size_t), alignof (limb_t));

and adjust the access accordingly.

Richard.

> Regards,
> /Niels
> 
> 

-- 
Richard Biener <rguenther at suse.de>
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