add a terrain_changed function for use with static terrain variables.

src/kernel/terrain.c

@@ -57,6 +57,17 @@ const char *terraindata[MAXTERRAINS] = {
 };
 
 static terrain_type *registered_terrains;
+static int terrain_changes = 1;
+
+bool terrain_changed(int *cache) {
+    assert(cache);
+    if (*cache != terrain_changes) {
+        *cache = terrain_changes;
+        return true;
+    }
+    return false;
+}
+
 
 void free_terrains(void)
 {
@@ -76,6 +87,7 @@ void free_terrains(void)
         }
         free(t);
     }
+    ++terrain_changes;
 }
 
 const terrain_type *terrains(void)
@@ -110,6 +122,7 @@ const terrain_type *get_terrain(const char *name) {
 terrain_type * get_or_create_terrain(const char *name) {
     terrain_type *terrain = terrain_find_i(name);
     if (!terrain) {
+        ++terrain_changes;
         terrain = (terrain_type *)calloc(sizeof(terrain_type), 1);
         if (terrain) {
             terrain->_name = strdup(name);

src/kernel/terrain.h

@@ -18,6 +18,7 @@ OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 #ifndef TERRAIN_H
 #define TERRAIN_H
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -68,12 +69,13 @@ extern "C" {
         struct terrain_type *next;
     } terrain_type;
 
-    extern terrain_type *get_or_create_terrain(const char *name);
-    extern const terrain_type *terrains(void);
-    extern const terrain_type *get_terrain(const char *name);
-    extern const char *terrain_name(const struct region *r);
+    terrain_type *get_or_create_terrain(const char *name);
+    const terrain_type *terrains(void);
+    const terrain_type *get_terrain(const char *name);
+    const char *terrain_name(const struct region *r);
+    bool terrain_changed(int *cache);
 
-    extern void init_terrains(void);
+    void init_terrains(void);
     void free_terrains(void);
 
 #ifdef __cplusplus

src/laws.c

@@ -246,9 +246,15 @@ static void calculate_emigration(region * r)
     int maxp = region_maxworkers(r);
     int rp = rpeasants(r);
     int max_immigrants = MAX_IMMIGRATION(maxp - rp);
+    static int terrain_cache;
+    static const terrain_type *t_volcano;
+    static const terrain_type *t_smoking;
 
-    if (r->terrain == newterrain(T_VOLCANO)
-        || r->terrain == newterrain(T_VOLCANO_SMOKING)) {
+    if (terrain_changed(&terrain_cache)) {
+        t_volcano = get_terrain("volcano");
+        t_smoking = get_terrain("activevolcano");
+    }
+    if (r->terrain == t_volcano || r->terrain == t_smoking) {
         max_immigrants = max_immigrants / 10;
     }