INTERFACE Bits;

Arithmetic for Modula-3, see doc for details

Abstract: Bits and Bytes

2/17/96 Harry George Initial version

IMPORT Word;

TYPE
  NYBBLE = BITS 4 FOR [0 .. 16_F];
  BYTE = BITS 8 FOR [0 .. 16_FF];

  (* Declare bit arrays (i.e.  bit maps) as needed.  BitArray = ARRAY
     [0..N] OF BITS 1 FOR [0..1]; *)

  ByteArray = REF ARRAY OF BYTE;

TYPE
  (* e.g., LOOPHOLE(my_cardinal,BigEndian).b1 *)
  AnyEndian = RECORD data: ARRAY [0 .. 3] OF BYTE;  END;

  BigEndian = RECORD b4, b3, b2, b1: BYTE;  END;

  LittleEndian = RECORD b1, b2, b3, b4: BYTE;  END;

PROCEDURE WhichEndian (): [-1 .. +1];

-1 means little-endian, +1 means big-endian.

PROCEDURE Fmt (x    : Word.T;
               nbits: [1 .. Word.Size] := 32;
               base : CARDINAL         := 2; (* typically 2 or 16 *)
  ): TEXT;

returns text for x, left padded to nbits length by 0 if necessary.

PROCEDURE Reverse (x    : Word.T;            (* given this number *)
                   nbits: [1 .. Word.Size];  (* using the low n bits *)
  ): Word.T;                     (* return reversed bit pattern *)

E.g., nbits = 4 ==> 00001011 becomes 00001101 NOTE: There are better ways to do this if you need to do a whole array, as in FFT. See xFFT.m3.

PROCEDURE HashPJW (READONLY str   : ARRAY OF CHAR;  (* given this string *)
                            n1, nn: CARDINAL;       (* using n1..nn *)
  ): CARDINAL;                   (* return hash value *)

P. Weinberger's hash. From the str buffer, using str[n1]..str[nn], make a hash value

PROCEDURE HashELF (READONLY str   : ARRAY OF CHAR;  (* given this string *)
                            n1, nn: CARDINAL;       (* using n1..nn *)
  ): CARDINAL;                   (* return hash value *)

ELF hash From the str buffer, using str[n1]..str[nn], make a hash value

END Bits.