Path: utzoo!attcan!uunet!pyrdc!ISIDAPS5!mike
From: mike@ISIDAPS5.UUCP (Mike Maloney)
Newsgroups: comp.lang.c
Subject: Absolute size of 'short'
Keywords: unsigned wrap-around
Message-ID: <214@ISIDAPS5.UUCP>
Date: 1 Aug 88 20:53:42 GMT
Lines: 35

Dear C-Heavies,

Is the size of a (signed or unsigned) short integer guarenteed to
be two bytes?  I need to manipulate and compare some unsigned ints
modulo 65536.  It would be clean and convenient to just let the
machine handle my wrap-around from 0 to 0xffff and verse-vica.

The following works fine on my Xenix-386 machine, but is it portable?
Note that the default integer size is 4 bytes, so the expression 'u'
inside the printf's is being converted.

	unsigned short u;

	u = 0xffff;
	u++;
	printf("0x%x\n",u);		==>  	0x0

	u = 0;
	u--;
	printf("0x%x\n",u);		==> 	0xffff

    Note however:
	u = 0xffff;
	u + 1 != 0		==> In the expression 'u + 1', 'u' is upwardly
				    converted to 4 bytes before adding 1.

    but
	(unsigned short)(u + 1) == 0


-- 

Mike Maloney				"The nice thing about standards
Integral Systems, Inc.			 is that there are so many to
Lanham Maryland				 choose from"  - Murphy