From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=0.6 required=5.0 tests=BAYES_00,TO_NO_BRKTS_FROM_MSSP autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,25aa3c7e1b59f7b5 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2002-01-04 07:42:35 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!netnews.com!newspeer.cwnet.com!newsfeed.frii.net!out.nntp.be!propagator-SanJose!in.nntp.be!newsranger.com!www.newsranger.com!not-for-mail Newsgroups: comp.lang.ada From: Ted Dennison References: <3C34BF2C.6030500@mail.com> <3C35675D.276C2D81@canal-plus.fr> Subject: Re: A case where Ada defaults to unsafe? Message-ID: X-Abuse-Info: When contacting newsranger.com regarding abuse please X-Abuse-Info: forward the entire news article including headers or X-Abuse-Info: else we will not be able to process your request X-Complaints-To: abuse@newsranger.com NNTP-Posting-Date: Fri, 04 Jan 2002 10:42:29 EST Organization: http://www.newsranger.com Date: Fri, 04 Jan 2002 15:42:29 GMT Xref: archiver1.google.com comp.lang.ada:18529 Date: 2002-01-04T15:42:29+00:00 List-Id: In article <3C35675D.276C2D81@canal-plus.fr>, Thierry Lelegard says... > >Maybe the actual question should be "why are there two distinct formats, >with and without short-circuit?" > >"and then" has an actual added value over "and" (the short-circuit). >On the other hand, what is the added value of "and"? What can be >achieved by "and" that could not be by "and then" (except side-effect, >which is a dirty practice)? Again, I wish people would read the rationale before saying stuff like this. It is exaplained there. One issue is that you may indeed want the side effects of both expressions (dirty practice or no). Another is that the compiler is not free to reorder your expressions for efficiency with the short-circuit forms, even if it turns out that you really don't care what order they are performed in (which is usually going to be the case). Another is that there are some circumstances where a short-circuit is going to be *slower* than a non-short circuit calculation. After all, a short-circuit implies an extra branch instruction, whereas normal "and" is a simple integer-unit operation. Plus, if the typical eventuality is to make it through to the last expression, then all those extra checks are a big waste. Now I know Robert Dewar is on record as saying that most of these issues either don't apply on modern processors, or were never taken advantage of by any compiler. But the above was the initial reasoning for not short-circuiting. --- T.E.D. homepage - http://www.telepath.com/dennison/Ted/TED.html No trees were killed in the sending of this message. However a large number of electrons were terribly inconvenienced.