The Look Up an Entry in a Balanced Binary Tree routine looks up
    an entry in a balanced binary tree.

    Format

      LIB$LOOKUP_TREE  treehead ,symbol ,user-compare-routine

                       ,new-node

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Arguments

 treehead

    OpenVMS usage:address
    type:         address
    access:       read only
    mechanism:    by reference

    Tree head for the binary tree. The treehead argument is the
    address of an unsigned longword that is this tree head.

 symbol

    OpenVMS usage:user_arg
    type:         longword (unsigned)
    access:       unspecified
    mechanism:    unspecified

    Key to be looked up in the binary tree.

 user-compare-routine

    OpenVMS usage:procedure
    type:         procedure value
    access:       function call (before return)
    mechanism:    by value

    User-supplied compare routine that LIB$LOOKUP_TREE calls to
    compare a symbol with a node. The value returned by the compare
    routine indicates the relationship between the symbol key and the
    current node.

 new-node

    OpenVMS usage:address
    type:         longword (unsigned)
    access:       write only
    mechanism:    by reference

    Location where the new symbol was found. The new-node argument
    is the address of an unsigned longword that is the new node
    location.