Bug in "comm" utility

[Doug Gwyn]

As you can see in the excerpt below, the UNIX "comm" utility makes a
non-portable assumption about pointer arithmetic in its compare() function.
Here is the quick fix I devised for the UNIX System V Release 2.0 source;
other versions of "comm" appear to be similar.

static char sccsid[] = "@(#)comm.c	1.2";
...
main(argc,argv)
char **argv;
{
	int	l;
	char	xlb1[LB+1],xlb2[LB+1];	/* DAG: allow for -- in compare() */
#define	lb1	(&xlb1[1])
#define	lb2	(&xlb2[1])
...
compare(a,b)
char *a,*b;
{
	register char *ra,*rb;

	ra = --a;
	rb = --b;
...