|32/64 bit non-portability A.M.King@ukc.ac.uk (2002-05-17)|
|Re: 32/64 bit non-portability firstname.lastname@example.org (2002-05-23)|
|Re: 32/64 bit non-portability derek@NOSPAMknosof.co.uk (dmjones) (2002-05-23)|
|Re: 32/64 bit non-portability email@example.com (Christian Bau) (2002-05-27)|
|Re: 32/64 bit non-portability firstname.lastname@example.org (Nick Maclaren) (2002-05-27)|
|From:||"Nick Maclaren" <email@example.com>|
|Date:||27 May 2002 20:52:35 -0400|
|Organization:||University of Cambridge, England|
|References:||02-05-085 02-05-097 02-05-134|
|Posted-Date:||27 May 2002 20:52:35 EDT|
Christian Bau <firstname.lastname@example.org> wrote:
>I think in the desktop computer world you will find quite a lot of
>code that assumes long == 32 bit, and a compiler might include some
>heuristics to find warning signs.
>Obviously, any cast from pointer to int/long if int/long is not large
>enough to hold that pointer value is a problem (if you keep long == 32
>bit, long long == pointer == 64 bit). Bitwise "and" between unsigned
>long and a constant like 0xfffffffe is a bad sign if long > 32 bit.
>Operations that swap bits around in an unsigned long, like (x << 16) |
>(x >> 16) if long > 32 bits. Warnings in these cases would be very
>much appreciated. And any use of the constant 4 as an argument in
>memset, memcpy, memcmp, fread, fwrite where you would expect sizeof
>Of course, people who are used to other kinds of machines won't make
>these kinds of mistakes. Well-written programs won't benefit much, but
>sadly many programs will.
Yes, I agree, but didn't make myself clear. A looked at a couple of
dozen 'typical' desktop programs in some detail, and there were
relatively few dependencies on the exact size of long, but a great
many (and much more serious ones) on size_t <= unsigned long, which is
what breaks in C99.
The main cause of 32-bit assumptions was using Internet addresses, and
the second one was in constructions like you mention. ANY
18-character hexadecimal constant starting with 0x8-0xf and used in an
operation involving long or unsigned long is worth flagging. As is
any memory operation with a length that is not a multiple of the size
of the address types (using sizeof!)
But, once I had excluded that sort of thing, I found very little.
Clean programs don't use the same long variable for an Internet
address and calculation in the same function without a clear
indication of which value is being used. And my experience in
compiling programs under our DEFAULT configuration of 64-bit IRIX
So what I meant was that example programs will add little. There are
a few simple checks that will pick up almost everything that you will
see in clean codes, and few programs will trigger these in more than a
few places. And the programs that many much more serious 32-bit
assumptions are likely to be so ghastly that they will trigger any
correctness or portability test, thoughout.
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