From: Jean-Christophe Filliatre <Jean-Christophe.Filliatre@lri.fr>
To: Chris Hecker <checker@d6.com>
Cc: caml-list@inria.fr
Subject: Re: [Caml-list] why does hashtbl not use lists?
Date: Tue, 10 Jul 2001 11:05:01 +0200 (MEST) [thread overview]
Message-ID: <15178.50493.314895.925129@pc803> (raw)
In-Reply-To: <4.3.2.7.2.20010710013127.02c06600@shell16.ba.best.com>
Chris Hecker writes:
>
> Why does hashtbl.ml (from the standard library) use the bucketlist
> variant instead of just the built in lists with tuples? Is there an
> efficiency thing going on here?
Yes, it saves 33% of memory. Indeed, a list of tuples will give blocks
like this:
______
|X|.|.|......>
---.-- _______
......> |X|a|b|
-------
that is, 6 words for each binding, whereas the bucketlist type will
give blocks like this:
_________
|X|a|b|.|....>
---------
that is, 4 words. (X stands for the block header, which is 1 word and
dots stand for pointers; sory for the ugly ASCII drawing).
(Beside saving memory, you also save time, by allocating one block
instead of two and also when destructuring the block to look inside,
since depth is 1 instead of 2.)
--
Jean-Christophe Filliatre
mailto:Jean-Christophe.Filliatre@lri.fr
http://www.lri.fr/~filliatr
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next prev parent reply other threads:[~2001-07-10 9:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-07-10 8:34 Chris Hecker
2001-07-10 9:00 ` Fergus Henderson
2001-07-10 9:05 ` Jean-Christophe Filliatre [this message]
2001-07-10 9:42 ` Fergus Henderson
2001-07-10 14:44 ` Xavier Leroy
2001-07-10 17:04 Charles Martin
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