[gnumeric] GCD: fix handling of zeros.

[Morten Welinder <mortenw src gnome org>]

commit bd906d433aff5f8542c25a0df39f46bfd8dae705
Author: Morten Welinder <terra gnome org>
Date:   Wed Jan 13 12:12:34 2010 -0500

    GCD: fix handling of zeros.

 NEWS                        |    3 +++
 plugins/fn-math/ChangeLog   |    5 +++++
 plugins/fn-math/functions.c |    9 +++++----
 3 files changed, 13 insertions(+), 4 deletions(-)
---
diff --git a/NEWS b/NEWS
index 6223446..f5755ab 100644
--- a/NEWS
+++ b/NEWS
@@ -44,6 +44,9 @@ Jody:
 	* More win32 build fixes (xslt for libgda & poppler).
 	* Fix pango test harness.
 
+Morten:
+	* Fix GCD border case.  [#606870]
+
 --------------------------------------------------------------------------
 Gnumeric 1.9.17
 
diff --git a/plugins/fn-math/ChangeLog b/plugins/fn-math/ChangeLog
index 4325086..36f700f 100644
--- a/plugins/fn-math/ChangeLog
+++ b/plugins/fn-math/ChangeLog
@@ -1,3 +1,8 @@
+2010-01-13  Morten Welinder  <terra gnome org>
+
+	* functions.c (range_gcd): Handle GCD(2,0)=2 as Excel, but err on
+	GCD(0,0).
+
 2009-12-23  Andreas J. Guelzow <aguelzow pyrshep ca>
 
 	* functions.c (compare_doubles): rename to 
diff --git a/plugins/fn-math/functions.c b/plugins/fn-math/functions.c
index 21823cc..7bd2778 100644
--- a/plugins/fn-math/functions.c
+++ b/plugins/fn-math/functions.c
@@ -70,9 +70,6 @@ static const gnm_float gnm_gcd_max = 1 / GNM_EPSILON;
 static gnm_float
 gnm_gcd (gnm_float a, gnm_float b)
 {
-	g_return_val_if_fail (a > 0 && a <= gnm_gcd_max, -1);
-	g_return_val_if_fail (b > 0 && b <= gnm_gcd_max, -1);
-
 	while (b > 0.5) {
 		gnm_float r = gnm_fmod (a, b);
 		a = b;
@@ -90,11 +87,15 @@ range_gcd (gnm_float const *xs, int n, gnm_float *res)
 
 		for (i = 0; i < n; i++) {
 			gnm_float thisx = gnm_fake_floor (xs[i]);
-			if (thisx <= 0 || thisx > gnm_gcd_max)
+			if (thisx < 0 || thisx > gnm_gcd_max)
 				return 1;
 			else
 				gcd_so_far = gnm_gcd (thisx, gcd_so_far);
 		}
+
+		if (gcd_so_far == 0)
+			return 1;
+
 		*res = gcd_so_far;
 		return 0;
 	} else