🚀 go-pugleaf

The following code prints "65135" instead of the expected "401" when
compiled with the "-O" flag.  The problem is at line 72: the shorts
are not signed extended before subtracting and stored in the int "adx".

This gcc version 1.30 on a Sun 3/50  running SunOS 3.5.

Tom Quinn                 Canadian Institute for Theoretical Astrophysics
trq@moose.cita.utoronto.ca
UUCP   - decvax!utgpu!moose!trq
BITNET - quinn@utorphys.bitnet
ARPA   - trq%moose.cita.toronto.edu@relay.cs.net

The compile:
gcc -g -v -O -c mfbline.c
gcc version 1.30
 /usr/local/lib/gcc-cpp -v -undef -D__GNU__ -D__GNUC__ -Dmc68000 -Dsun -Dunix -D__OPTIMIZE__ -D__HAVE_68881__ -Dmc68020 mfbline.c /tmp/cca02948.cpp
GNU CPP version 1.30
 /usr/local/lib/gcc-cc1 /tmp/cca02948.cpp -quiet -dumpbase mfbline.c -g -O -version -o /tmp/cca02948.s
GNU C version 1.30 (68k, MIT syntax) compiled by GNU C version 1.30.
 as -mc68020 /tmp/cca02948.s -o mfbline.o
gcc -v mfbline.o
gcc version 1.30
 ld /lib/crt0.o /lib/Mcrt1.o mfbline.o /usr/local/lib/gcc-gnulib -lc
150}a.out
65135

The code:
------------------------------------------------------------------------
typedef struct _DDXPoint *DDXPointPtr;
typedef struct _Box *BoxPtr;
typedef struct _DDXPoint {
    short x, y;
} DDXPointRec;
typedef struct _Box {
    short x1, y1, x2, y2;
} BoxRec;
main()
{
    DDXPointPtr ptinit;
    ptinit = (DDXPointPtr) malloc(2*sizeof(DDXPointRec));
    ptinit[0].x = -1;
    ptinit[1].x = 400;
    ptinit[0].y = 400;
    ptinit[1].y = 900;
    mfbLineSS(0, 2, ptinit);
}
mfbLineSS( mode, npt, pptInit)
    int mode;		 
    int npt;		 
    DDXPointPtr pptInit;
{
    int nboxInit;
    register int nbox;
    BoxPtr pboxInit;
    register BoxPtr pbox;
    int nptTmp;
    DDXPointPtr ppt;		 
    DDXPointRec pt1;
    DDXPointRec pt2;
    int xorg, yorg;		 
    int adx;		 
    int ady;
    int signdx;		 
    int signdy;
    int e, e1, e2;		 
    int axis;			 
    DDXPointRec pt1Orig;	 
    DDXPointRec pt2Orig;	 
    xorg = yorg = 0;
    ppt = pptInit;
    nptTmp = npt;
    if (mode == 	0	)
    {
	while(nptTmp--)
	{
	    ppt->x += xorg;
	    ppt++->y += yorg;
	}
    }
    else
    {
	ppt->x += xorg;
	ppt->y += yorg;
	nptTmp--;
	while(nptTmp--)
	{
	    ppt++;
	    ppt->x += (ppt-1)->x;
	    ppt->y += (ppt-1)->y;
	}
    }
    ppt = pptInit;
    while(--npt)
    {
	nbox = nboxInit;
	pbox = pboxInit;
	pt1 = *ppt++;
	pt2 = *ppt;
	{
	    adx = pt2.x - pt1.x;
	    ady = pt2.y - pt1.y;
	    signdx = ((adx) < 0 ? -1 : ((adx) > 0 ? 1 : 0)) ;
	    signdy = ((ady) < 0 ? -1 : ((ady) > 0 ? 1 : 0)) ;
	    adx = ((adx) > 0 ? (adx) : -(adx)) ;
	    ady = ((ady) > 0 ? (ady) : -(ady)) ;
	    if (adx > ady)
	    {
		axis = 0 ;
		e1 = ady*2;
		e2 = e1 - 2*adx;
		e = e1 - adx;
	    }
	    else
	    {
		axis = 1 ;
		e1 = adx*2;
		e2 = e1 - 2*ady;
		e = e1 - ady;
	    }
	    pt1Orig = pt1;
	    pt2Orig = pt2;
	    printf("%d\n", adx);
	}  
    }  
}