Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!mailrus!cornell!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.lang.misc
Subject: Re: Dynamic array dimensioning
Message-ID: <6847@june.cs.washington.edu>
Date: 5 Jan 89 19:27:20 GMT
References: <117400002@uxa.cso.uiuc.edu>
Reply-To: pardo@cs.washington.edu (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 31

In article <117400002@uxa.cso.uiuc.edu> gsg0384@uxa.cso.uiuc.edu writes:
>[What languages have run-time local array sizing?]
>[Impossible to do in FORTRAN?]
>[Is dynamic sizing too costly to implement?]

Most of the ``very dynamic'' languages, e.g., Smalltalk have automatic
dimension resizing.  Others, such as Ada, Algol, Simula, and PL/1 have
array size bound and procedure entry time.  GNU cc also allows this as
a nonstandard extension.

[To the best of my knowledge] all standard FORTRANs must be able to
run on a machine that has no dynamic memory allocation.  Runtime size
binding definitely requires memory allocation.

Dynamic sizing is more expensive than static dimensioning for at least
the following reasons:

* The stack frame doesn't have a fixed size.  Thus you need two
  registers dedicated to the call frame.  Even if you don't care about
  using an extra register, you still have to load/reset them (time and
  code space).
* Fewer array indexing optimizations are possible.

Whether this is ``too expensive'' depends entirely on what you want.

Hope this helps.

	;-D on  ( A dynamic kind of guy )  Pardo
-- 
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