Date: Tue, 12 Oct 1999 16:33:42 +0200 (MET DST)
From: grenie AT math DOT jussieu DOT fr (Loic Grenie)
Message-Id: <199910121433.QAA29095@riemann.math.jussieu.fr>
To: pgcc AT delorie DOT com
Subject: Bug in bug report about sign extension elimination
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8bit
Reply-To: pgcc AT delorie DOT com

    I forgot to send the file... I can be also a little bit more precise. It
  seems that the compiler is confused about register contents. As far as I
  can tell it also seems it does not do correct sign extension. It's visible
  at the end of the first small loop (the one with r++; i++;).

            Loïc


typedef struct {
    short	x1, y1, x2, y2;
} BoxRec, *BoxPtr;

#define ExchangeRects(a, b)	\
{				\
    BoxRec	t;		\
				\
    t = rects[a];		\
    rects[a] = rects[b];	\
    rects[b] = t;		\
}

void QuickSortRects(BoxPtr rects, int numRects)
{
    register int        y1;
    register int        x1;
    register int        i, j;
    register BoxPtr     r;

    do {
	if (numRects == 2) {
	    if (rects[0].y1 > rects[1].y1 ||
		    (rects[0].y1 == rects[1].y1 && rects[0].x1 > rects[1].x1))
		ExchangeRects(0, 1);
	    return;
	}
	ExchangeRects(0, numRects >> 1);
	y1 = rects[0].y1;
	x1 = rects[0].x1;

	/* Partition array */
	i = 0;
	j = numRects;
	do
	{
	    r = &(rects[i]);
	    do
	    {
		r++;
		i++;
	    } while (i != numRects &&
		     (r->y1 < y1 || (r->y1 == y1 && r->x1 < x1)));
	    r = &(rects[j]);
	    do
	    {
		r--;
		j--;
	    } while (y1 < r->y1 || (y1 == r->y1 && x1 < r->x1));
	    if (i < j)
		ExchangeRects(i, j);
	} while (i < j);
	ExchangeRects(0, j);
	if (numRects-j-1 > 1)
	    QuickSortRects(&rects[j+1], numRects-j-1);
	numRects = j;
    } while (numRects > 1);
}