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Article View: comp.lang.lisp.mcl
Article #602

Re: map-array

#602
From: Guillaume Cartier
Date: Fri, 11 Dec 1992 19:12
27 lines
1601 bytes
<---
| Based on the Code of Bill St.Clair for faster-climits I tried to write a
| general map-array function,
| both a mcl specific and a portable version.
| 
| Then I compared this construct to mapc for sequences
| 
| To my surprise, the mapping an array was slower than mapping over a list.
| Am I missing something ?
--->

Yes!

It is true that access to a specific element of an array in generaly faster
than access to a specific element of a list. But, in this case, we are not accessing elements individualy but mapping over the whole structure.

Mapping over an array involves accessing every element individualy (each
time having to do at least a multiplication and an addition) where as
mapping over a list involves simple pointer indirections which are very
fast.

*********************************************************************
* Guillaume Cartier                 (514) 844-5294 (maison)         *
* L.A.C.I.M.                        (514) 987-4290 (bureau)         *
* Universite du Quebec a Montreal   (514) 987-8477 (telecopieur)    *
* Montreal, Quebec, Canada          cartier@math.uqam.ca (internet) *
*********************************************************************
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Path: arc1-ca.pugleaf.net!sparky!uunet!stanford.edu!apple!cambridge.apple.com!cartier@math.uqam.ca
From: cartier@math.uqam.ca (Guillaume Cartier)
Newsgroups: comp.lang.lisp.mcl
Subject: Re: map-array
Message-ID: <9212111912.AA08784@mipsmath.math.uqam.ca>
Date: 11 Dec 92 19:12:37 GMT
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