improve checker messages - simulation

src/common/m_helper.fpp

@@ -36,7 +36,8 @@ module m_helper
               f_create_bbox, &
               s_print_2D_array, &
               f_xor, &
-              f_logical_to_int
+              f_logical_to_int, &
+              f_approx_equal
 
 contains
 
@@ -532,4 +533,34 @@ contains
         end if
     end function f_logical_to_int
 
+    !> This procedure checks if two floating point numbers of kind(0d0) are within tolerance.
+    !! @param a First number.
+    !! @param b Second number.
+    !! @param tol_input Relative error (default = 1d-6).
+    !! @return Result of the comparison.
+    logical function f_approx_equal(a, b, tol_input) result(res)
+        ! Reference: https://floating-point-gui.de/errors/comparison/
+
+        real(kind(0d0)), intent(in) :: a, b
+        real(kind(0d0)), optional, intent(in) :: tol_input
+        real(kind(0d0)) :: tol
+
+        if (present(tol_input)) then
+            if (tol_input <= 0d0) then
+                call s_mpi_abort('tol_input must be positive. Exiting ...')
+            end if
+            tol = tol_input
+        else
+            tol = 1d-6
+        end if
+
+        if (a == b) then
+            res = .true.
+        else if (a == 0d0 .or. b == 0d0 .or. (abs(a) + abs(b) < tiny(a))) then
+            res = (abs(a - b) < (tol*tiny(a)))
+        else
+            res = (abs(a - b)/min(abs(a) + abs(b), huge(a)) < tol)
+        end if
+    end function f_approx_equal
+
 end module m_helper