🚀 go-pugleaf

There are two bugs in the "portable" routine "getsh()" in the file
screen/setupterm.c.  The first bug is that the comparison "if (*p == 0377)"
is incorrect if characters are signed by default.  If *p contained the
BYTE value '\377', sign extension would make it so *p != 0377 since 0377
is an integer and will NOT be sign extended.

The second bug is that "rv = *p++" will do sign extension (for systems with
characters being signed).  What we want is to sign extend on ONLY the
"high part"; more precisely, we want to sign extend ONLY on the assignment
that follows which puts the high byte in and NOT on the assignment that puts
the low byte in.

[ I suspect that if this routine was used, it was used on a machine where
  characters are unsigned. ]

The original getsh() follows:

getsh(p)
register char *p;
{
	register int rv;
	if(*p == 0377)
		return -1;
	rv = *p++;
	rv += *p * 256;
	return rv;
}

the following should do the trick:

getsh(p)
register char *p;
{
	register int rv;

	rv = *((unsigned char *) p);
	if(rv == 0377)
		return -1;	/* This is a pretty common case */
	return rv + (*++p * 256);
}

Instead of this though, I use the following macro (since this is for a machine
with signed characters):

#define		getsh(ip)	(*((unsigned char *) ip) | (*(ip+1) << 8))

Folks on machines with unsigned character implementations could use:

#define		getsh(ip)	((*ip == 0377) ? -1 : (*ip | (*(ip+1) << 8))))

[ This should serve the perpose required as stated in the comment above
  the macro definitions. ]

		Mike Laman, NCR @ Torrey Pines
		UUCP: {ucbvax,philabs,sdcsla}!sdcsvax!laman