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From: diamond@tkou02.enet.dec.com (diamond@tkovoa)
Newsgroups: comp.std.c
Subject: Re: constant expressions
Message-ID: <1927@tkou02.enet.dec.com>
Date: 17 Aug 90 01:37:43 GMT
References: <1916@tkou02.enet.dec.com> <13550@smoke.BRL.MIL> <1923@tkou02.enet.dec.com> <13555@smoke.BRL.MIL> <1924@tkou02.enet.dec.com> <1990Aug16.152345.29177@zoo.toronto.edu>
Reply-To: diamond@tkou02.enet.dec.com (diamond@tkovoa)
Organization: Digital Equipment Corporation Japan , Tokyo
Lines: 24

In article <1990Aug16.152345.29177@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>In article <1924@tkou02.enet.dec.com> diamond@tkou02.enet.dec.com (diamond@tkovoa) writes:
>>Besides clearly NOT REQUIRING translation-time evaluations, I have also seen
>>clear REASONS for this non-requirement.  If your target machine can handle
>>128-bit ints, your host machine is not required to provide a simulator.
>Given that the compiler is required to do type checking (must produce a
>diagnostic for a violation of the rules), it's going to have to evaluate
>constant expressions as subscripts in array declarations.

Section 3.5.4.2 has a SEMANTICS rule about compatible array types.
I cannot find a similar CONSTRAINTS rule.  Therefore it seems that the
compiler is permitted but not required to do this type checking, and
is not required to produce a diagnostic for a violation.

>Provided it can get exactly the same effect, which is going to be tricky.
>The *preprocessor* is not required to emulate target arithmetic, but the
>rest of the compiler is nailed down pretty strictly.

The rest of the compiler is nailed down IF IT CHOOSES to compute
constant expressions.  It can always choose to leave a computation for
execution time.
-- 
Norman Diamond, Nihon DEC     diamond@tkou02.enet.dec.com
This is me speaking.  If you want to hear the company speak, you need DECtalk.