Copyright (C) 1994, Digital Equipment Corp.
INTERFACE Word;
A Word.T w represents a sequence of Word.Size bits
w(0), ..., w(Word.Size-1).
It also represents the unsigned number
sum of 2^(i) * w(i) for i in 0, ..., Word.Size-1.
TYPE
T = INTEGER;
(* encoding is implementation-dependent; e.g., 2's complement. *)
CONST
Size : INTEGER = BITSIZE (T); (* implementation-dependent *)
PROCEDURE Plus (x, y: T): T; (* (x + y) MOD 2^[Word.Size] *)
PROCEDURE Times (x, y: T): T; (* (x * y) MOD 2^[Word.Size] *)
PROCEDURE Minus (x, y: T): T; (* (x - y) MOD 2^[Word.Size] *)
PROCEDURE Divide (x, y: T): T; (* x divided by y *)
PROCEDURE Mod (x, y: T): T; (* x MOD y *)
PROCEDURE LT (x, y: T): BOOLEAN; (* x < y *)
PROCEDURE LE (x, y: T): BOOLEAN; (* x <= y *)
PROCEDURE GT (x, y: T): BOOLEAN; (* x > y *)
PROCEDURE GE (x, y: T): BOOLEAN; (* x >= y *)
PROCEDURE And (x, y: T): T; (* Bitwise AND of x and y *)
PROCEDURE Or (x, y: T): T; (* Bitwise OR of x and y *)
PROCEDURE Xor (x, y: T): T; (* Bitwise XOR of x and y *)
PROCEDURE Not (x: T): T; (* Bitwise complement of x *)
PROCEDURE Shift (x: T; n: INTEGER): T;
For all i such that both i and i - n are in the range [0 .. Word.Size - 1],
bit i of the result equals bit i - n of x. The other bits of the result are
0. Thus, shifting by n > 0 is like multiplying by 2^(n)
PROCEDURE LeftShift (x: T; n: [0..Size-1]): T;
= Shift (x, n)
PROCEDURE RightShift (x: T; n: [0..Size-1]): T;
= Shift (x, -n)
PROCEDURE Rotate (x: T; n: INTEGER): T;
Bit i of the result equals bit (i - n) MOD Word.Size of x.
PROCEDURE LeftRotate (x: T; n: [0..Size-1]): T;
= Rotate (x, n)
PROCEDURE RightRotate (x: T; n: [0..Size-1]): T;
= Rotate (x, -n)
PROCEDURE Extract (x: T; i, n: CARDINAL): T;
Take n bits from x, with bit i as the least significant bit, and return them
as the least significant n bits of a word whose other bits are 0. A checked
runtime error if n + i > Word.Size.
PROCEDURE Insert (x, y: T; i, n: CARDINAL): T;
Return x with n bits replaced, with bit i as the least significant bit, by
the least significant n bits of y. The other bits of x are unchanged. A
checked runtime error if n + i > Word.Size.
END Word.