Category : Files from Magazines
Archive   : DDJ-9003.ZIP
Filename : DUNTEMAN.LST

STRUCTURED PROGRAMMING COLUMN
by Jeff Duntemann





[LISTING ONE]

(*---------------------------------------------------*)
(* BITWISE.MOD *)
(* Definition Module *)
(* *)
(* Bit-manipulation routines for Modula-2 *)
(* *)
(* by Jeff Duntemann *)
(* For DDJ : March 1990 *)
(* Last modified 11/25/89 *)
(*---------------------------------------------------*)


DEFINITION MODULE Bitwise;

PROCEDURE And(A,B : CARDINAL) : CARDINAL;

PROCEDURE Or(A,B : CARDINAL) : CARDINAL;

PROCEDURE Xor(A,B : CARDINAL) : CARDINAL;

PROCEDURE Not(Target : CARDINAL) : CARDINAL;

PROCEDURE SetBit(Target : CARDINAL; BitNum : CARDINAL) : CARDINAL;

PROCEDURE ClearBit(Target : CARDINAL; BitNum : CARDINAL) : CARDINAL;

PROCEDURE TestBit(Target : CARDINAL; BitNum : CARDINAL) : BOOLEAN;

PROCEDURE SHR(Target : CARDINAL; By : CARDINAL) : CARDINAL;

PROCEDURE SHL(Target : CARDINAL; By : CARDINAL) : CARDINAL;

END Bitwise.



[LISTING TWO]

(*---------------------------------------------------*)
(* BITWISE.MOD *)
(* Implementation Module *)
(* *)
(* Bit-manipulation routines for Modula-2 *)
(* *)
(* by Jeff Duntemann *)
(* For DDJ : March 1990 *)
(* Last modified 11/25/89 *)
(* *)
(* NOTES ON THE CODE: *)
(* *)
(* In all cases below, BitNum MOD 16 is used as a *)
(* means of ensuring that BitNum will be in the *)
(* range of 0..15. MOD 16 divides by 16 but returns *)
(* the remainder, which cannot be over 15 when you *)
(* divide by 16. *)
(*---------------------------------------------------*)

IMPLEMENTATION MODULE Bitwise;

VAR
I : CARDINAL;
TempSet : BITSET;


PROCEDURE And(A,B : CARDINAL) : CARDINAL;

BEGIN
RETURN CARDINAL(BITSET(A) * BITSET(B));
END And;


PROCEDURE Or(A,B : CARDINAL) : CARDINAL;

BEGIN
RETURN CARDINAL(BITSET(A) + BITSET(B));
END Or;


PROCEDURE Xor(A,B : CARDINAL) : CARDINAL;

BEGIN
RETURN CARDINAL(BITSET(A) / BITSET(B));
END Xor;


PROCEDURE Not(Target : CARDINAL) : CARDINAL;

BEGIN
RETURN CARDINAL({0..15} - BITSET(Target));
END Not;


PROCEDURE SetBit(Target : CARDINAL; BitNum : CARDINAL) : CARDINAL;

BEGIN
TempSet := BITSET(Target); (* INCL does not operate on expressions! *)
INCL(TempSet,BitNum MOD 16);
RETURN CARDINAL(TempSet); (* Cast the target back to type CARDINAL *)
END SetBit;


PROCEDURE ClearBit(Target : CARDINAL; BitNum : CARDINAL) : CARDINAL;

BEGIN
TempSet := BITSET(Target); (* EXCL does not operate on expressions! *)
EXCL(TempSet,BitNum MOD 16);
RETURN CARDINAL(TempSet); (* Cast the target back to type CARDINAL *)
END ClearBit;


PROCEDURE TestBit(Target : CARDINAL; BitNum : CARDINAL) : BOOLEAN;

BEGIN
IF (BitNum MOD 16) IN BITSET(Target) THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END;
END TestBit;


PROCEDURE SHR(Target : CARDINAL; By : CARDINAL) : CARDINAL;

BEGIN
FOR I := 1 TO By DO
Target := Target DIV 2;
END;
RETURN Target;
END SHR;


PROCEDURE SHL(Target : CARDINAL; By : CARDINAL) : CARDINAL;

BEGIN
FOR I := 1 TO By DO
Target := Target * 2;
END;
RETURN Target;
END SHL;


END Bitwise.