example11-26.vhd

vhdl 实例 通过实例学习vhdl 编程

LIBRARY IEEE;
USE IEEE.Std_Logic_1164.ALL;
PACKAGE pak IS
  PROCEDURE add (in1, in2 : IN Std_Logic_Vector;
                  carry_in : IN Std_Logic;
                  sum : OUT Std_Logic_Vector;
                  carry_out : OUT Std_Logic);
  FUNCTION inc (x : IN Std_Logic_Vector) RETURN Std_Logic_Vector;
  FUNCTION dec (x : IN Std_Logic_Vector) RETURN Std_Logic_Vector;
  FUNCTION intval (val : IN Std_Logic_Vector) RETURN INTEGER;
END pak;

PACKAGE BODY pak IS
  PROCEDURE add (in1, in2 : IN Std_Logic_Vector;
                  carry_in : IN Std_Logic;
                  sum : OUT Std_Logic_Vector;
                  carry_out : OUT Std_Logic) IS
    VARIABLE sumv, av, bv : Std_Logic_Vector (in1'LENGTH - 1 DOWNTO 0);
    VARIABLE carry : Std_Logic;
  BEGIN
    av := in1;
    bv := in2;
    carry := carry_in;
    FOR i IN 0 TO sumv'HIGH LOOP
      sumv (i) := av (i) XOR bv (i) XOR carry;
      carry := (av (i) AND bv (i)) OR (av (i) AND carry) OR (bv (i) AND carry);
    END LOOP;
    carry_out := carry;
    sum := sumv;
  END add;

  FUNCTION inc (x : IN Std_Logic_Vector) RETURN Std_Logic_Vector IS
    VARIABLE xv : Std_Logic_Vector (x'LENGTH - 1 DOWNTO 0);
  BEGIN
    xv := x;
    FOR i IN 0 TO xv'HIGH LOOP
      IF xv (i) = '0' THEN
        xv (i) := '1';
        EXIT;
      ELSE
        Xv (i) := '0';
      END IF;
    END LOOP;
    RETURN xv;
  END inc;

  FUNCTION dec (x : IN Std_Logic_Vector) RETURN Std_Logic_Vector IS
    VARIABLE xv : Std_Logic_Vector (x'LENGTH - 1 DOWNTO 0);
  BEGIN
    xv := x;
    FOR i IN 0 TO xv'HIGH LOOP
      IF xv (i) = '1' THEN
        xv (i) := '0';
        EXIT;
      ELSE
        Xv (i) := '1';
      END IF;
    END LOOP;
    RETURN xv;
  END dec;

  FUNCTION intval (val : IN Std_Logic_Vector) RETURN INTEGER IS
    VARIABLE valv : Std_Logic_Vector (val'LENGTH - 1 DOWNTO 0);
    VARIABLE sum : INTEGER := 0;
  BEGIN
    valv := val;
    FOR i IN valv'LOW TO valv'HIGH LOOP
      IF valv (i) = '1' THEN
        sum := sum + (2 ** i);
      END IF;
    END LOOP;
  RETURN sum;
  END intval;
END pak;