use the entire range of RAND_MAX, not the range divided by 32

Author: Goober5000

code/model/modelinterp.cpp

@@ -3603,8 +3603,22 @@ void submodel_get_two_random_points(int model_num, int submodel_num, vec3d *v1,
 		return;
 	}
 
-	int vn1 = (myrand()>>5) % nv;
-	int vn2 = (myrand()>>5) % nv;
+#ifndef NDEBUG
+	if (RAND_MAX < nv)
+	{
+		static int submodel_get_two_random_points_warned = false;
+		if (!submodel_get_two_random_points_warned)
+		{
+			polymodel *pm = model_get(model_num);
+			Warning(LOCATION, "RAND_MAX is only %d, but submodel %d for model %s has %d vertices!  Explosions will not propagate through the entire model!", RAND_MAX, submodel_num, pm->filename, nv);
+			submodel_get_two_random_points_warned = true;
+		}
+	}
+#endif
+
+	Assert(nv > 0);	// Goober5000 - to avoid div-0 error
+	int vn1 = myrand() % nv;
+	int vn2 = myrand() % nv;
 
 	*v1 = *Interp_verts[vn1];
 	*v2 = *Interp_verts[vn2];
@@ -3641,9 +3655,22 @@ void submodel_get_two_random_points_better(int model_num, int submodel_num, vec3
 			return;
 		}
 
+#ifndef NDEBUG
+		if (RAND_MAX < nv)
+		{
+			static int submodel_get_two_random_points_warned = false;
+			if (!submodel_get_two_random_points_warned)
+			{
+				polymodel *pm = model_get(model_num);
+				Warning(LOCATION, "RAND_MAX is only %d, but submodel %d for model %s has %d vertices!  Explosions will not propagate through the entire model!", RAND_MAX, submodel_num, pm->filename, nv);
+				submodel_get_two_random_points_warned = true;
+			}
+		}
+#endif
+
 		Assert(nv > 0);	// Goober5000 - to avoid div-0 error
-		int vn1 = (myrand()>>5) % nv;
-		int vn2 = (myrand()>>5) % nv;
+		int vn1 = myrand() % nv;
+		int vn2 = myrand() % nv;
 
 		*v1 = tree->point_list[vn1];
 		*v2 = tree->point_list[vn2];