64 bit architectures and C/C++

[Blair P. Houghton]

In article <168 at shasta.Stanford.EDU> shap at shasta.Stanford.EDU (shap) writes:
>It seems to me that 64 bit architectures are going to
>introduce some nontrivial problems with C and C++ code.

Nope.  They're trivial if you didn't assume 32-bit architecture,
which you shouldn't, since many computers still have 36, 16, 8,
etc.-bit architectures.

>I want to start a discussion going on this topic.  Here are some seed
>questions:

Here's some fertilizer (but most of you consider it that way, at
any time :-) ):

>1. Do the C/C++ standards need to be extended to cover 64-bit
>environments, or are they adequate as-is?

The C standard allows all sorts of data widths, and specifies
a scad of constants (#defines, in <limits.h> to let you use
these machine-specific numbers in your code, anonymously.

>2. If a trade-off has to be made between compliance and ease of
>porting, what's the better way to go?

If you're compliant, you're portable.

>3. If conformance to the standard is important, then the obvious
>choices are
>
>	short	16 bits
>	int	32 bits
>	long	64 bits
>	void *	64 bits

The suggested choices are:

	short	<the shortest integer the user should handle; >= 8 bits> 
	int	<the natural width of integer data on the cpu; >= a short>
	long	<the longest integer the user should handle; >= an int>
	void *  <long enough to specify any location legally addressable>

There's no reason for an int to be less than the full
register-width, and no reason for an address to be limited
to the register width.

An interesting side-effect of using the constants is that
you never need to know the sizes of these things on your
own machine; i.e., use CHAR_BIT (the number of bits in a char)
and `sizeof int' (the number of chars in an int) and you'll
never need to know how many bits an int contains.

>How bad is it for sizeof(int) != sizeof(long). 

It's only bad if you assume it's not true. (I confess:  I peeked.
I saw Chris' answer, and I'm not going to disagree.)

>4. Would it be better not to have a 32-bit data type and to make int
>be 64 bits?  If so, how would 32- and 64- bit programs interact?

Poorly, if at all.  Data transmission among architechures
with different bus sizes is a hairy issue of much aspirin.
The only portable method is to store and transmit the data
in some width-independent form, like morse-code or a text
format (yes, ascii is a 7 or 8 bits wide, but it's a
_common_ form of data-width hack, and if all else fails,
you can hire people to read and type it into your
machine).

>Looking forward to a lively exchagne...

				--Blair
				  "Did anyone NOT bring potato salad?"