Xref: utzoo comp.lang.c:16428 comp.std.c:845
Path: utzoo!utgpu!watmath!clyde!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c,comp.std.c
Subject: Sizes, alignments, and maxima (was: Contiguous Arrays)
Message-ID: <11838@haddock.ima.isc.com>
Date: 22 Feb 89 22:51:06 GMT
References: <2508@ssc-vax.UUCP> <8943@alice.UUCP> <830@atanasoff.cs.iastate.edu>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Followup-To: comp.std.c
Organization: Interactive Systems, Boston
Lines: 24

In article <830@atanasoff.cs.iastate.edu> hascall@atanasoff.cs.iastate.edu (John Hascall) writes:
>In article <8943@alice.UUCP> ark@alice.UUCP (Andrew Koenig) writes:
>>For that reason it's hard to see how a C implementation could possibly
>>do anything but put [an array] in contiguous memory.
>
>How about:  Assume int's are (say) 2 bytes.  Assume further that ... all
>accesses must be on an 8-byte boundary.

Then sizeof(int) is 8, and the elements of the array consists of contiguous
8-byte units, of which only two bytes are significant.  This sounds much like
a Cray-2, in fact.

Question for comp.std.c (to which I've redirected followups): I've been told
that the Cray-2 has sizeof(int) == 8, yet INT_MAX == 0x7FFFFFFF (i.e. the
arithmetic is only accurate to 4 bytes when using int).  Is this legal in a
conforming implementation?  I think I can prove that UINT_MAX must be 2*^64-1,
but I'm less sure about INT_MAX.  Section 3.1.2.5 has a restriction to binary
architectures, which by the definition in the footnote seems to require every
bit except the highest to represent a power of two; should this be interpreted
as a requirement that 2*^63-1 must be representable in an 8-byte int?

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint
(I've implicitly assumed 8-bit bytes above, simply because it would be too
cumbersome to type the more correct expressions involving CHAR_BIT.)