VHDL Programming

Subprograms and Packages 125

TYPE ninevaltab IS ARRAY(nineval’LOW TO

nineval’HIGH) OF nineval;

TYPE strengthtab IS ARRAY(strength’LOW TO

strength’HIGH) OF nineval;

FUNCTION resolve9( s: ninevalvec) RETURN nineval;

END ninepack;

The package body contains the resolution function (package bodies are

discussed near the end of this chapter).

PACKAGE BODY ninepack IS

FUNCTION resolve9( s: ninevalvec) RETURN nineval IS

VARIABLE result: nineval;

CONSTANT get_strength : ninevaltab :=

(Z, --Z0

Z, --Z1

Z, --ZX

R, --R0

R, --R1

R, --RX

F, --F0

F, --F1

F); --FX

CONSTANT x_tab : strengthtab :=

(ZX, --Z

RX, --R

FX); --F

BEGIN

IF s’LENGTH = 0 THEN RETURN ZX; END IF;

result := s(0);

FOR i IN s’RANGE LOOP

IF get_strength(result) < get_strength(s(i)) THEN

result := s(i);

ELSIF get_strength(result) = get_strength(s(i)) THEN

IF result /= s(i) THEN

result := x_tab(get_strength(result));

END IF;

END IF;

END LOOP;

RETURN result;

END resolve9;

END ninepack;

The package ninepackdeclares a number of types used in this example,

including some array types to make the resolution function easier to