Function            rsub - subtract two REAL numbers

  Syntax              struct REAL rsub(struct REAL val, struct REAL sval,
                                       int precision);

  Prototype in        real.h

  Remarks             sval is subtracted from val. The result will have
                      precision decimal places. See rsub() for more
                      details.

  Return value        returns sval minus val to the specified precision.
                      If an error occurred, the returned structure's
                      values will all be -1 (rint, rfrac and precision)
                      and _rmatherr will contain the error code.

                      Refer to the section SIMULATED FP MATH for further
                      details.

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