Fortran: handle RADIX kind in IEEE_SET_ROUNDING_MODE

Make sure that calling IEEE_SET_ROUNDING_MODE with RADIX=10 does not
affect the binary rounding mode.

2022-09-21  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>

libgfortran/

	* ieee/ieee_arithmetic.F90 (IEEE_SET_ROUNDING_MODE): Handle
	RADIX argument better.

gcc/testsuite/

	* gfortran.dg/ieee/rounding_3.f90: New test.

gcc/testsuite/gfortran.dg/ieee/rounding_3.f90

@@ -0,0 +1,27 @@
+! { dg-do run }
+
+  ! Test IEEE_GET_ROUNDING_MODE and IEEE_SET_ROUNDING_MODE
+  ! with a RADIX argument
+  use, intrinsic :: ieee_arithmetic
+  implicit none
+
+  real :: sx1
+  type(ieee_round_type) :: r
+
+  if (ieee_support_rounding(ieee_up, sx1) .and. &
+      ieee_support_rounding(ieee_down, sx1)) then
+
+    call ieee_set_rounding_mode(ieee_up)
+    call ieee_get_rounding_mode(r)
+    if (r /= ieee_up) stop 1
+
+    call ieee_set_rounding_mode(ieee_down, radix=2)
+    call ieee_get_rounding_mode(r, radix=2)
+    if (r /= ieee_down) stop 2
+
+    call ieee_set_rounding_mode(ieee_up, radix=10)
+    call ieee_get_rounding_mode(r, radix=2)
+    if (r /= ieee_down) stop 3
+  end if
+
+end

libgfortran/ieee/ieee_arithmetic.F90

@@ -1075,6 +1075,12 @@ contains
       end subroutine
     end interface
 
+    ! We do not support RADIX = 10, and such calls should not
+    ! modify the binary rounding mode.
+    if (present(RADIX)) then
+      if (RADIX == 10) return
+    end if
+
     call helper(ROUND_VALUE%hidden)
   end subroutine