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From: cadsi@ccad.uiowa.edu (CADSI)
Newsgroups: comp.lang.c++
Subject: Re: 64 bit architectures and C/C++
Message-ID: <1991May1.163446.20707@ccad.uiowa.edu>
Date: 1 May 91 16:34:46 GMT
References: <13261@goofy.Apple.COM>
Organization: CAD-Research, U. of Iowa, Iowa City, Iowa
Lines: 33

From article <13261@goofy.Apple.COM>, by turk@Apple.COM (Ken "Turk" Turkowski):
> jac@gandalf.llnl.gov (James A. Crotinger) writes:
> 
> 
>>  Anyone want to comment on experiences with Crays? I believe the C
>>compilers have sizeof(int) = sizeof(short) = sizeof(long) == 46 or 64
>>bits, depending on a compile time flag (Crays can do 46 bit integer
>>arithmetic using the vectorizing floating point processors, so that is
>>the default). 
> 
>>  Binary communications between Crays and other computers is something
>>I haven't done, mostly because Cray doesn't support IEEE floating point.
> 
> Crays are a pain.  Structures are padded to 64 bits, so you waste a lot
> of memory in arrays if your structures only have 16 bits.
> 
> I thought the number was 48 bits, but you might be right.  I seem to recall
> that logical operations couldn't work with 64 bits, but arithmetic operations
> could, or vice versa.
>...

to further these comments note that on a CRAY, a (char *) is a bit-packed
structure itself.  In particular, the lower 48 bits are a pointer to
the word in memory where the character exists.  The top 3 bits of the
64-bit pointer are an index to the byte of the word of the actual
character.  Thus, an (int *) cannot be conveniently cast to a (char *).
I hate it when that happens.

|----------------------------------------------------------------------------|
|Tom Hite					|  The views expressed by me |
|Manager, Product development			|  are mine, not necessarily |
|CADSI (Computer Aided Design Software Inc.	|  the views of CADSI.       |
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