synth: add static neg for signed.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/synth/synth-ieee-numeric_std.adb b/src/synth/synth-ieee-numeric_std.adb
index 738146014..0a75d0576 100644
--- a/src/synth/synth-ieee-numeric_std.adb
+++ b/src/synth/synth-ieee-numeric_std.adb
@@ -238,4 +238,32 @@ package body Synth.Ieee.Numeric_Std is
       return Res;
    end Mul_Sgn_Sgn;
 
+   function Neg_Sgn (V : Std_Logic_Vector) return Std_Logic_Vector
+   is
+      pragma Assert (V'First = 1);
+      Len : constant Integer := V'Last;
+      subtype Res_Type is Std_Logic_Vector (1 .. Len);
+      Res : Res_Type;
+      Vb, Carry : Sl_X01;
+   begin
+      if Len < 1 then
+         return Null_Vec;
+      end if;
+      Carry := '1';
+      for I in 0 .. Len - 1 loop
+         Vb := Sl_To_X01 (V (V'Last - I));
+         if Vb = 'X' then
+            --assert NO_WARNING
+            --  report "NUMERIC_STD.""+"": non logical value detected"
+            --  severity warning;
+            Res := (others => 'X');
+            exit;
+         end if;
+         Vb := Not_Table (Vb);
+         Res (Res'Last - I) := Xor_Table (Carry, Vb);
+         Carry := And_Table (Carry, Vb);
+      end loop;
+      return Res;
+   end Neg_Sgn;
+
 end Synth.Ieee.Numeric_Std;