avoid unnecessary initialisation of conditional masks

include/evalhyd/evalp.hpp

@@ -292,18 +292,19 @@ namespace evalhyd
         }
 
         // retrieve dimensions
-        std::size_t n_sit = q_prd_.shape(0);
-        std::size_t n_ltm = q_prd_.shape(1);
         std::size_t n_tim = q_prd_.shape(3);
-        std::size_t n_msk = t_msk_.size() > 0 ? t_msk_.shape(2) :
-                            (m_cdt.size() > 0 ? m_cdt.shape(1) : 1);
 
         // generate masks from conditions if provided
         auto gen_msk = [&]()
         {
-            XB4 c_msk = xt::zeros<bool>({n_sit, n_ltm, n_msk, n_tim});
-            if (m_cdt.size() > 0)
+            if ((t_msk_.size() < 1) && (m_cdt.size() > 0))
             {
+                std::size_t n_sit = q_prd_.shape(0);
+                std::size_t n_ltm = q_prd_.shape(1);
+                std::size_t n_msk = m_cdt.shape(1);
+
+                XB4 c_msk = xt::zeros<bool>({n_sit, n_ltm, n_msk, n_tim});
+
                 for (std::size_t s = 0; s < n_sit; s++)
                 {
                     for (std::size_t l = 0; l < n_ltm; l++)
@@ -319,9 +320,13 @@ namespace evalhyd
                         }
                     }
                 }
-            }
 
-            return c_msk;
+                return c_msk;
+            }
+            else
+            {
+                return XB4({});
+            }
         };
         const XB4 c_msk = gen_msk();