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Newsgroups: comp.lang.fortran
From: nos...@see.signature (Richard Maine)
Date: Sun, 8 Apr 2007 21:28:36 -0700
Local: Mon, Apr 9 2007 12:28 am
Subject: Re: Transfer and variables that don't use all their storage space.
Brooks Moses <bmoses-nos...@cits1.stanford.edu> wrote: My phrasing of that isn't the world's best (or even second best :-)), > Richard Maine wrote: > I think I'm confused as to what it means, in practical terms, when "the > standard ... requires disallowed behavior". but I was basically agreeing with what seemed to be your logic. If the standard requires behavior that the standard also disallows, I think one can deduce that code that does that is non-conforming (by one of those basic section 1.4 arguments). Thus the compiler can do anything. > Doing that would either require that the entire initialization- Ok. I'm the naive one here, but I think that is the behavior anticipated > expression evaluation mechanism store all logical variables in a way > that records all eight bytes of "target storage" even though they are > almost never meaningful, by the standard. If variables of a type (the 8-byte logical one or any other) can be used as repositories of arbitrary bits by transfer, then it seems to me that you need to store all those bits. Perhaps in special cases, you can deduce that you can optimize storage of some of them away, but that seems like an optimization to me. > If I understand your above comments correctly, you've agreed that this No. I'm using a back door argument to explain why the code is illegal. > is illegal code, but you also explicitly agreed with the second half of > my first paragraph (the bit starting with "In particular," which says > that transfer(transfer(-5_8, L), -5_8) must return -5, not 1. It seems > completely counterintuitive to me that the compiler is required to > produce a specific result for illegal code. However, that's what I'm > understanding you to be saying. More or less a proof by contradiction, which is perhaps why it seems contradictory. :-) I arise at a contradiction if I assume the code is standard conforming. The contradiction is that the standard requires a result that the standard also prohibits. Thus, I conclude that the assumption of standard conformance is false. > Would it be allowable, at least, for a compiler to throw an error and I think you could argue that. But then you might get users who > refuse to compile "transfer(transfer(-5_8, L), -5_8)" at all? considered it a poor quality of implementation; that one is harder. I have trouble imagining why anyone would ever want to do such a strange thing, but James Buskirk can probably come up with something useful. :-) I think the more "obvious" thing to do is to use all 8 bytes. But I -- You must Sign in before you can post messages.
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