We wish to implement a limit checker, that checks whether a signed
integer is out of specified bounds.  The integer and bounds are
represented as standard logic vectors of the subtype word, declared
in the package project_util as:

	subtype word is std_logic_vector(31 downto 0);

We can use a comparison function that compares integers represented as
bit vectors.  The function is declared as:

	function "<" ( bv1, bv2 : bit_vector ) return boolean;

The entity declaration and architecure body for the limit checker are
shown in Figure 21-2.  The process performs the comparisons by
converting the word values to bit vectors, using the conversion
function word_to_bitvector.  Note that we cannot use the function
To_bitvector itself in the actual part of the association list, as it
has two parameters, not one.  Note also that the result type of the
conversion function in this example must be a constrained array type,
in order to specify the array bounds for the actual value passed to
the comparison function.