-- Copyright © 1993 by  McGraw-Hill, Inc. and Zainalabedin Navabi

-- FIGURE 9.12 




-- BODY OF PAR_UTILITIES PACKAGE OF PAR_LIBRARY :

PACKAGE body par_utilities IS

  FUNCTION "XOR" (a, b : qit) RETURN qit IS
    CONSTANT qit_or_table : qit_2d := (
                            ('0','1','1','X'),
                            ('1','0','0','X'),
                            ('1','0','0','X'),
                            ('X','X','X','X'));
  BEGIN
    RETURN qit_or_table (a, b);
  END "XOR";

  FUNCTION "AND" (a,b : qit_vector) RETURN qit_vector IS
    VARIABLE r : qit_vector (a'RANGE);
  BEGIN
    loop1: FOR i IN a'RANGE LOOP
      r(i) := a(i) AND b(i);
    END LOOP loop1;
    RETURN r;
  END "AND";
  --
  FUNCTION "OR" (a,b: qit_vector) RETURN qit_vector IS
    VARIABLE r: qit_vector (a'RANGE);
  BEGIN
    loop1: FOR i IN a'RANGE LOOP
      r(i) := a(i) OR b(i);
    END LOOP loop1;
  RETURN r;
  END "OR";
  --
  FUNCTION "NOT" (a: qit_vector) RETURN qit_vector IS
    VARIABLE r: qit_vector (a'RANGE);
  BEGIN
    loop1: FOR i IN a'RANGE LOOP
      r(i) := NOT a(i);
    END LOOP loop1;
    RETURN r;
  END "NOT";
  --
  FUNCTION add_cv (a, b : qit_vector; cin : qit) RETURN qit_vector IS
    --left bits are sign bit
    VARIABLE r, c: qit_vector (a'LEFT + 2 DOWNTO 0);
    -- two extra bits in r are: msb for overflow, next carry
    VARIABLE a_sign, b_sign: qit;
  BEGIN
    a_sign := a(a'LEFT); 
    b_sign := b(b'LEFT);
    r(0) := a(0) XOR b(0) XOR cin;
    c(0) := ((a(0) XOR b(0)) AND cin) OR (a(0) AND b(0));
    FOR i IN 1 TO (a'LEFT) LOOP
      r(i) := a(i) XOR b(i) XOR c(i-1);
      c(i) := ((a(i) XOR b(i)) AND c(i-1)) OR (a(i) AND b(i));
    END LOOP;
    r(a'LEFT+1) := c(a'LEFT);
    IF a_sign = b_sign AND r(a'LEFT) /= a_sign
      THEN r(a'LEFT+2) := '1'; --overflow
    ELSE r(a'LEFT+2) := '0'; END IF;
    RETURN r;
  END add_cv;
    
  FUNCTION sub_cv (a, b : qit_vector; cin : qit) RETURN qit_vector IS
    VARIABLE not_b : qit_vector (b'LEFT DOWNTO 0);
    VARIABLE not_c : qit;
    VARIABLE r : qit_vector (a'LEFT + 2 DOWNTO 0);
  BEGIN
    not_b := NOT b;
    not_c := NOT cin;
    r := add_cv (a, not_b, not_c);    
    RETURN r;
  END sub_cv;
  
  FUNCTION set_if_zero (a : qit_vector) RETURN qit IS
    VARIABLE zero : qit := '1';
  BEGIN
    FOR i IN a'RANGE LOOP
      IF a(i) /= '0' 
        THEN zero := '0'; EXIT; 
      END IF;
    END LOOP;
    RETURN zero;
  END set_if_zero;

END par_utilities;
--