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From: mlandau@bbn.com (Matt Landau)
Newsgroups: comp.lang.c
Subject: Arithmetic Types  [WAS Re: 32bit = 16bit x 16bit]
Message-ID: <9873@slate.BBN.COM>
Date: Fri, 16-Oct-87 11:58:44 EDT
Article-I.D.: slate.9873
Posted: Fri Oct 16 11:58:44 1987
Date-Received: Sat, 17-Oct-87 21:56:29 EDT
References: <1912@gryphon.CTS.COM>
Reply-To: mlandau@bbn.com (Matt Landau)
Followup-To: comp.lang.c
Organization: Stately Wayne Manor
Lines: 41
Summary: don't count on anything - use typedefs

In comp.lang.c (<1912@gryphon.CTS.COM>), mhatter@pnet02.CTS.COM (Patrick E. Hughes) 
writes:
>In addition to a small letter I sent to the author of the original message
>that started this whole mess, I might suggest one thing if you plan on porting
>many C programs: Don't Use Ints
>
>Use char, use long, use float, and since they don't change size you're always
>set.  

Don's change size, eh?  You want signed or unsigned chars?  And how many bits
are there in a char anyway?  Eight?  Nine?  Thirteen?  The language doesn't
specify anything about chars, or longs (except that sizeof(long) >= sizeof(int),
which isn't much help), or much of anything else where the size and representation
of arithmetic types are concerned.

If you're concerned about being portable, use typedefs.  I generally try to
typedef signed and unsigned types of 8, 16, and 32 bits, and some kind of
short and long flaoting point types.  For most machines, the integer types
work out to:

	typedef	unsigned char	UINT8;
	typedef	unsigned char	BYTE;		/* I like BYTE, so what? */
	typedef	unsigned short	UINT16;
	typedef	unsigned int	UINT32;
	typedef char		INT8;
	typedef short		INT16;
	typedef int		INT32;

though on Intel-based PC's and other perverse hardware, things change a bit.
Note that these are *minimum* number of bits, not *exact* number of bits;
Anything that requires exact sizes is probably going to need its own set
of application-specific typedefs anyway.

The point is, the code only uses "int" or "char" when the details don't matter
and it's important to get the "best" performance (which one assumes you get by
using the "natural size" integer -- that's what "int" in C *means*).  If it 
matters how many bits something is, using the typedefs insures that the code 
is portable to any machine for which all of the appropriate types can be defined.
--
 Matt Landau			Waiting for a flash of enlightenment
 mlandau@bbn.com			  in all this blood and thunder