Xref: utzoo comp.sys.ibm.pc:22158 comp.sys.intel:596
Path: utzoo!utgpu!watmath!mks!egisin
From: egisin@mks.UUCP (Eric Gisin)
Newsgroups: comp.sys.ibm.pc,comp.sys.intel
Subject: Re: correct code for pointer subtraction
Summary: please read my code
Message-ID: <600@mks.UUCP>
Date: 13 Dec 88 17:24:33 GMT
References: <597@mks.UUCP> <8377@bloom-beacon.MIT.EDU> <8455@sequent.UUCP>
Organization: Mortice Kern Systems, Waterloo, Ont.
Lines: 24

In article <8455@sequent.UUCP>, sch@sequent.UUCP (Steve Hemminger) writes:
> I believe the ANSI std and K&R say pointer subtraction is only allowed inside
> one data structure/array.  Since the small/medium/large model only allows
> arrays <64K, only a 16bit result needs to be computed. Any code that
> depends on subtracting pointers into two totally seperate arrays is
> non-portable.

Please read my code. I have two pointers to "s", a single object.
Declaring "s" with 1 or 10000 makes no difference.
And the pointers are seperated by 60000, which is less than 64K.

struct six {		/* HINT: this struct is 6 bytes long */
	int i[3];
};

int diff(struct six far* p, struct six far* q) {
  	return p - q;
}

main(void) {
	struct six s[1];
	printf("%d\n", diff(s+10000, s));	/* 10000 */
	printf("%d\n", diff(s, s+100));		/* -100 */
}