Function            lpow - raise a base to an exponent

  Syntax              long lpow(long base, int exponent);

  Prototype in        real.h

  Remarks             lpow() calculates base raised to the exponent
                      power. If base is zero or exponent is negative
                      (lpow() does not handle either of these cases), it
                      is treated as a singularity error (_rmatherror =
                      RSING). Underflow and overflow are trapped with the
                      appropriate error value in _rmatherror.

  Return value        returns zero if an error occurred, with an
                      appropriate error value in _rmatherror, otherwise
                      the calculated value (non-zero).

  Note                This function is called internally by several
                      simulated FP functions. Refer to the section
                      SIMULATED FP MATH for further details.

  See also            real.h
                      _rmatherror