DLABAD takes as input the values computed by DLAMCH for underflow and
 overflow, and returns the square root of each of these values if the
 log of LARGE is sufficiently large.  This subroutine is intended to
 identify machines with a large exponent range, such as the Crays, and
 redefine the underflow and overflow limits to be the square roots of
 the values computed by DLAMCH.  This subroutine is needed because
 DLAMCH does not compensate for poor arithmetic in the upper half of
 the exponent range, as is found on a Cray.

          SMALL is DOUBLE PRECISION
          On entry, the underflow threshold as computed by DLAMCH.
          On exit, if LOG10(LARGE) is sufficiently large, the square
          root of SMALL, otherwise unchanged.

          LARGE is DOUBLE PRECISION
          On entry, the overflow threshold as computed by DLAMCH.
          On exit, if LOG10(LARGE) is sufficiently large, the square
          root of LARGE, otherwise unchanged.