code: def to_signed(cls, t):
          
          assert isinstance(t, SymbolTYPE)
          t = t.final
          assert t.is_basic
          if cls.is_unsigned(t):
              return {cls.ubyte: cls.byte_,
                      cls.uinteger: cls.integer,
                      cls.ulong: cls.long_}[t]
          if cls.is_signed(t) or cls.is_decimal(t):
              return t
          return cls.unknown
docs: Return signed type or equivalent