Description

   The DCX$EXPAND_INIT routine initializes the context area for the
   expansion of data records.

   Call the DCX$EXPAND_INIT routine as the first step in the
   expansion (or restoration) of compressed data records to their
   original state.

   Before you call DCX$EXPAND_INIT, read the length of the
   compressed file from the compression/expansion function (the
   map). Invoke LIB$GET_VM to get the necessary amount of storage
   for the function. LIB$GET_VM returns the address of the first
   byte of the storage area.