The UNPACK procedure copies components of a packed array  to  an
  unpacked array variable.

  Syntax:

     UNPACK( z,a,i )

  The parameter 'z' is a packed array.  The parameter  'a'  is  an
  unpacked  array  variable.   The  parameter  'i' is the starting
  value of the index of 'a'.

  The number of components in 'a' must be greater than or equal to
  the  number  of components in 'z'.  The UNPACK procedure assigns
  the components of 'z', starting  with  z[lower  bound],  to  the
  array  'a',  starting with a[i], until all the components in 'z'
  are used.

  In general, when specifying 'i', keep in  mind  that  the  upper
  bound of 'a' (that is, n) must be greater than or equal to i + v
  - u, where 'v' is the upper bound of 'a' and 'u'  is  the  lower
  bound  of 'a'.  That is, ORD(n) must be greater than or equal to
  ORD(i) + ORD(v) - ORD(u).

  Normally, you cannot pass the individual components of a  packed
  array to formal VAR parameters; you must unpack the array first.