ADAS Subroutine xxbase

      subroutine xxbase( a , ia , base_a , value , code )
c-----------------------------------------------------------------------
c
c  ****************** fortran77 subroutine: xxbase ********************
c
c  purpose: to produce a number from representation as a*base^ia
c           protected against underflow and overflow.
c
c  input : (r*8)  a       = mantissa part of number
c  input : (r*8)  ia      = characteristic part of number
c  input : (c*(*))code    = 'zero' => zero a delivered if underflow
c                           'min'  => minimum number delivered
c  output: (r*8)  value   = evaluated number
c
c
c routines:
c          routine    source    brief description
c          ------------------------------------------------------------
c          xxbasr     adas      convert scaled number to new base
c          i4unit     adas      fetch unit number for output of messages
c
c author:  Hugh Summers
c          JET K1/1/61
c          Tel. 01235-46-4459
c date:    07-05-2008
c
c
c version  : 1.1
c date     : 07-05-2008
c modified : Hugh Summers
c              - first version.
c-----------------------------------------------------------------------
      CHARACTER*(*)       CODE
      INTEGER             IA
      REAL*8              A,           BASE_A,      VALUE