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Re: [Chicken-hackers] [PATCH] [CHICKEN 5] Change numerics representation

From: felix . winkelmann
Subject: Re: [Chicken-hackers] [PATCH] [CHICKEN 5] Change numerics representations
Date: Tue, 04 Oct 2016 16:19:15 +0200

> On Tue, Oct 4, 2016 at 4:00 AM, <address@hidden> wrote:
> > > We could still get rid of the tagged pointer type.  After some more
> >
> > > thought on the matter, I believe they're mostly worthless.
> >
> > "They" means tagged pointers? I agree.
> >
> I continue to disagree.  Tagged pointers make it possible to have
> dynamically type-safe or type-dispatched treatment of C objects referred to
> by the pointer side.  Logically it is equivalent to encapsulate the raw
> pointer in a record, but record dereference is much slower than pointer
> dereference for whatever reason, so it adds substantial overhead.

"Substantial" may be a bit strong, though the overhead is indeed there.
AFAIK, tagged pointers are seldom used. If indeed they were used instead
of raw pointers everywhere in the FFI (say, by generally tagging each
pointer of a known type), then the situation would be different, of course.

I don't feel strong enough to assess this. Any takers?


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