[gcalctool] Don't crash if currency rates have not been solved

[Robert Ancell <rancell src gnome org>]

commit 5f536b4f1cef21bd59a93b7b147d27a3c5355f1a
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Feb 1 09:10:53 2011 +1100

    Don't crash if currency rates have not been solved

 src/unit-category.c |    8 +++++---
 src/unit.c          |   24 ++++++++++++++++++------
 src/unit.h          |    4 ++--
 3 files changed, 25 insertions(+), 11 deletions(-)
---
diff --git a/src/unit-category.c b/src/unit-category.c
index 972ef08..94f33ef 100644
--- a/src/unit-category.c
+++ b/src/unit-category.c
@@ -91,9 +91,11 @@ unit_category_convert(UnitCategory *category, const MPNumber *x, const char *x_u
     unit_z = get_unit(category, z_units);
     if (!unit_x || !unit_z)
         return FALSE;
-  
-    unit_convert_from(unit_x, x, &t);
-    unit_convert_to(unit_z, &t, z);
+
+    if (!unit_convert_from(unit_x, x, &t))
+        return FALSE;
+    if (!unit_convert_to(unit_z, &t, z))
+        return FALSE;
 
     return TRUE;
 }
diff --git a/src/unit.c b/src/unit.c
index ed12c5e..a529e86 100644
--- a/src/unit.c
+++ b/src/unit.c
@@ -97,7 +97,7 @@ get_variable(const char *name, MPNumber *z, void *data)
 }
 
 
-static void
+static gboolean
 solve_function(const gchar *function, const MPNumber *x, MPNumber *z)
 {
     MPEquationOptions options;
@@ -110,35 +110,47 @@ solve_function(const gchar *function, const MPNumber *x, MPNumber *z)
     options.get_variable = get_variable;
     options.callback_data = (void *)x;
     ret = mp_equation_parse(function, &options, z, NULL);
-    if (ret)
+    if (ret) {
         g_warning("Failed to convert value: %s", function);
+        return FALSE;
+    }
+
+    return TRUE;
 }
 
 
-void
+gboolean
 unit_convert_from(Unit *unit, const MPNumber *x, MPNumber *z)
 {
     if (unit->priv->from_function)
-        solve_function(unit->priv->from_function, x, z);
+        return solve_function(unit->priv->from_function, x, z);
     else {
         // FIXME: Hack to make currency work
         const MPNumber *r;
         r = currency_manager_get_value(currency_manager_get_default(), unit->priv->name);
+        if (!r)
+            return FALSE;
         mp_divide(x, r, z);
+
+        return TRUE;
     }
 }
 
 
-void
+gboolean
 unit_convert_to(Unit *unit, const MPNumber *x, MPNumber *z)
 {
     if (unit->priv->from_function)
-        solve_function(unit->priv->to_function, x, z);
+        return solve_function(unit->priv->to_function, x, z);
     else {
         // FIXME: Hack to make currency work
         const MPNumber *r;
         r = currency_manager_get_value(currency_manager_get_default(), unit->priv->name);
+        if (!r)
+            return FALSE;
         mp_multiply(x, r, z);
+
+        return TRUE;
     }
 }
 
diff --git a/src/unit.h b/src/unit.h
index 9a1eb0f..459a2d6 100644
--- a/src/unit.h
+++ b/src/unit.h
@@ -38,9 +38,9 @@ gboolean unit_matches_symbol(Unit *unit, const gchar *symbol);
 
 const GList *unit_get_symbols(Unit *unit);
 
-void unit_convert_from(Unit *unit, const MPNumber *x, MPNumber *z);
+gboolean unit_convert_from(Unit *unit, const MPNumber *x, MPNumber *z);
 
-void unit_convert_to(Unit *unit, const MPNumber *x, MPNumber *z);
+gboolean unit_convert_to(Unit *unit, const MPNumber *x, MPNumber *z);
 
 gchar *unit_format(Unit *unit, MPNumber *x);