[glib] gdate: Add overflow precondition checks for g_date_[add|subtract]_*()

[Philip Withnall <pwithnall src gnome org>]

commit 38080bad05e40d4a33cbfe0ab179d3b422540a0b
Author: Philip Withnall <withnall endlessm com>
Date:   Thu Apr 12 18:06:03 2018 +0100

    gdate: Add overflow precondition checks for g_date_[add|subtract]_*()
    
    These turn undefined or hard-to-detect misbehaviour into a well-defined
    critical warning and early return.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=335731

 glib/gdate.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)
---
diff --git a/glib/gdate.c b/glib/gdate.c
index 0f30a5934..4ec92994a 100644
--- a/glib/gdate.c
+++ b/glib/gdate.c
@@ -1667,6 +1667,7 @@ g_date_add_days (GDate *d,
     g_date_update_julian (d);
 
   g_return_if_fail (d->julian);
+  g_return_if_fail (ndays <= G_MAXUINT32 - d->julian_days);
   
   d->julian_days += ndays;
   d->dmy = FALSE;
@@ -1720,13 +1721,16 @@ g_date_add_months (GDate *d,
   if (!d->dmy) 
     g_date_update_dmy (d);
 
-  g_return_if_fail (d->dmy);  
-  
+  g_return_if_fail (d->dmy);
+  g_return_if_fail (nmonths <= G_MAXUINT - (d->month - 1));
+
   nmonths += d->month - 1;
   
   years  = nmonths/12;
   months = nmonths%12;
-  
+
+  g_return_if_fail (years <= G_MAXUINT16 - d->year);
+
   d->month = months + 1;
   d->year  += years;
   
@@ -1808,8 +1812,9 @@ g_date_add_years (GDate *d,
   if (!d->dmy) 
     g_date_update_dmy (d);
 
-  g_return_if_fail (d->dmy);  
-  
+  g_return_if_fail (d->dmy);
+  g_return_if_fail (nyears <= G_MAXUINT16 - d->year);
+
   d->year += nyears;
   
   if (d->month == 2 && d->day == 29)