Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!bbn.com!mesard
From: mesard@bbn.com (Wayne Mesard)
Newsgroups: comp.lang.c
Subject: Re: C optimizer
Summary: Maybe pure funcitons should have to wear chastity belts.
Keywords: C pure function optimization
Message-ID: <36034@bbn.COM>
Date: 15 Feb 89 15:04:55 GMT
References: <515@larry.UUCP> <9648@smoke.BRL.MIL>
Sender: news@bbn.COM
Reply-To: mesard@BBN.COM (Wayne Mesard)
Organization: Bolt Beranek and Newman Inc., Cambridge MA
Lines: 20

In article <9648@smoke.BRL.MIL> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
>There is no standard mechanism for an application to declare its own
>functions as "pure"; however, if the compiler has access to all files
>it may be able to make such a determination itself.

Anyone want to challenge (by way of counter-example) the hypothesis that

  A function which is entirely composed of known "pure" operations*
  is, itself, pure.

* Where pure operations is defined as functions that produce no side
effects and return deterministic values, and most operators (excluding
assignment to dereferenced pointers and globals).  Hint: Sleep(3) would,
I believe, be labelled "pure" under this definition, so something's
still missing.

-- 
unsigned *Wayne_Mesard();
MESARD@BBN.COM           
BBN, Cambridge, MA