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To: Sara Golemon <pollita@php.net>
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Date: 29 Jul 2004 11:36:43 -0400
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Subject: Re: [PHP-DEV] GOTO operator
From: robert@interjinn.com (Robert Cummings)

On Thu, 2004-07-29 at 11:04, Sara Golemon wrote:
> > Note
> > ----
> > Goto jumping is O(1) if getting to the jump destination doesn't require
> > a hash lookup due to "wuring" of the destination at compile time. If a
> > hash lookup is required then it is probably something like O(lg n) which
> > is still superior in efficiency to O(n). Additionally, while it is true
> > that an O(lg n) lookup might be necessary at compile time to find the
> > pointer to the labeled code block, this is a one time event and has
> > little bearing on the efficiency overall when during runtime the goto
> > might be hit thousands or millions of times.
> >
> *this* implementation of GOTO requires a hash lookup, however it could be
> reworked to use the same backpatching as the ZEND_JMP ops used with
> conditional statements.  While doing that would speed execution time by
> skipping the hash lookup, it'd slow compile time and remove the ability to
> use complex expressions as goto targets (i.e.  goto "foo$i"; ).

I'm not sure whether this is feasible or not, but perhaps a mix of
compile-time/runtime logic is possible. If the argument of the goto is a
literal then a compile-time jump hook is created, otherwise the argument
is evaluated at run-time. This would provide the best of both worlds,
but as I said I have no idea as to its feasibility.

Cheers,
Rob.
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