Add API for R797.

src/iapws_api.f90

@@ -67,6 +67,31 @@ pure subroutine Tsat(ps, Ts)
     Ts = r4_Ts(ps)
 
 end subroutine
+
+pure subroutine waterproperty(p, T, prop)result(res)
+    !! Compute water properties at pressure p in MPa and temperature T in Kelvin.
+    !! The adequate region is selected according to p and T.
+    !! Returns NaN if no adequate region is found.
+    !!
+    !! Available properties:
+    !!     * v: specific volume
+    !!     * u: specific internal energy
+    !!     * s: specific entropy
+    !!     * h: specific enthalpy
+    !!     * cp: specific isobaric heat capacity
+    !!     * cv: specific isochoric heat capacity
+    !!     * w: speed of sound
+
+    ! parameters
+    real(dp), intent(in) :: p                 !! Pressure in MPa.
+    real(dp), intent(in) :: T                 !! Pressure in K.
+    character(len=*), intent(in) :: prop      !! Property
+
+    ! results
+    real(dp) :: res
+
+    res = ieee_value(1.0_dp, ieee_quiet_nan)
+end subroutine
 ! ------------------------------------------------------------------------------