Function            rnegate - change sign

  Syntax              struct REAL *rnegate(struct REAL *rx);

  Prototype in        real.h

  Remarks             rnegate changes the sign of rx. Since REALs are
                      structures and not actual variables, you cannot
                      simply say rx = -rx;

                      Refer to the section SIMULATED FP MATH for further
                      details.

  Return value        rnegate returns a pointer to the negated real rx.

  See also            _r_minpre, _rmatherr
                      radd(), rceil(), rdiv(), rfloor(), rnormalize(),
                      rsign(), rsub()