From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 25 Oct 2013 19:55:15 +0000 (-0400)
Subject: Suppress -0 in the C field of lines computed by line_construct_pts().
X-Git-Tag: REL9_4_BETA1~1011
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=43fe90f66a;p=postgresql

Suppress -0 in the C field of lines computed by line_construct_pts().

It's not entirely clear why some PPC machines are generating -0 here, since
the underlying computation should be exactly 0 - 0.  Perhaps there's some
wider-than-nominal-precision calculations happening?  Anyway, the best way
to avoid platform-dependent results seems to be to explicitly reset -0 to
regular zero.
---

diff --git a/src/backend/utils/adt/geo_ops.c b/src/backend/utils/adt/geo_ops.c
index 25f0bfd394..41178a6540 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));