[goffice] go_range_increasing, go_range_decreasing: Add preconditions.

[Morten Welinder <mortenw src gnome org>]

commit 3c26174918afe1aa19fee14d63c7b3433925952b
Author: Morten Welinder <terra gnome org>
Date:   Fri Aug 20 11:37:36 2010 -0400

    go_range_increasing, go_range_decreasing: Add preconditions.

 ChangeLog                   |    5 +++++
 goffice/math/go-rangefunc.c |    2 ++
 2 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 19c2e6b..931d29b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2010-08-20  Morten Welinder  <terra gnome org>
+
+	* goffice/math/go-rangefunc.c (go_range_increasing)
+	(go_range_decreasing): Add preconditions.
+
 2010-08-19  Jean Brefort  <jean brefort normalesup org>
 
 	* plugins/plot_surface/gog-xyz-surface.c
diff --git a/goffice/math/go-rangefunc.c b/goffice/math/go-rangefunc.c
index a9239b7..8558234 100644
--- a/goffice/math/go-rangefunc.c
+++ b/goffice/math/go-rangefunc.c
@@ -249,6 +249,7 @@ int
 SUFFIX(go_range_increasing) (DOUBLE const *xs, int n)
 {
 	int i;
+	g_return_val_if_fail (n == 0 || xs != NULL, 0);
 	for (i = 1; i < n; i++)
 		if (xs[i - 1] >= xs[i])
 			return 0;
@@ -259,6 +260,7 @@ int
 SUFFIX(go_range_decreasing) (DOUBLE const *xs, int n)
 {
 	int i;
+	g_return_val_if_fail (n == 0 || xs != NULL, 0);
 	for (i = 1; i < n; i++)
 		if (xs[i - 1] <= xs[i])
 			return 0;