Re: pgsql: Tweak "line" test to avoid negative zeros on some platforms

Peter Eisentraut <peter_e@gmx.net> writes:
> Tweak "line" test to avoid negative zeros on some platforms

I had been playing around with that last night on a PPC-era Mac,
hoping to get rid of the problem by twiddling the expressions in
line_construct_pts().  The only thing I could find to fix it
was the brute-force approach:

diff --git a/src/backend/utils/adt/geo_ops.c b/src/backend/utils/adt/geo_ops.c
index 25f0bfd..41178a6 100644
--- a/src/backend/utils/adt/geo_ops.c
+++ b/src/backend/utils/adt/geo_ops.c
@@ -1116,6 +1116,9 @@ line_construct_pts(LINE *line, Point *pt1, Point *pt2)
         line->A = (pt2->y - pt1->y) / (pt2->x - pt1->x);
         line->B = -1.0;
         line->C = pt1->y - line->A * pt1->x;
+        /* on some platforms, the preceding expression tends to produce -0 */
+        if (line->C == 0.0)
+            line->C = 0.0;
 #ifdef GEODEBUG
         printf("line_construct_pts- line is neither vertical nor horizontal (diffs x=%.*g, y=%.*g\n",
                DBL_DIG, (pt2->x - pt1->x), DBL_DIG, (pt2->y - pt1->y));


While this is surely pretty ugly, I think it is less ugly and more robust
than what you've done here.  Comments?

            regards, tom lane