Bit Manipulation Functions for C02 Programs

This module contains functions to shift and rotate the bits in a byte,
and to extract, combine, swap and duplicate nybbles in a byte.  

At the beginning of the program use the directives

  #include <stddef.h02>
  #include <bitlib.h02>

The following functions are defined:

  r = shiftl(b,n)       Shifts byte b by n bits to the left and returns 
                        the result in r. If n is 0, the byte is not 
                        shifted, and if n greater than 8, the returned
                        value will be 0.

  r = shiftr(b,n)       Shifts byte b by n bits to the right and returns 
                        the result in r. If n is 0, the byte is not 
                        shifted, and if n greater than 8, the returned
                        value will be 0.

  r = rotl(b,n)         Rotate byte b by n bits to the left and returns 
                        the result in r, with the high bit rotated into
                        the low bit on each rotation. If n is 0, the 
                        byte is not rotated, and any value of n greater 
                        than 8, will return the same result as n modulo 8.

  r = rotr(b,n)         Rotate byte b by n bits to the right and returns 
                        the result in r, with the high bit rotated into
                        the low bit on each rotation. If n is 0, the 
                        byte is not rotated, and any value of n greater 
                        than 8, will return the same result as n modulo 8.

  b = pack(l,r);        Packs the low nybbles of bytes l and r into a 
                        single byte, with l becoming the left (or high) 
                        nybble and r becoming the right (or low) nybble.
                        and returns the packed byte in b.

  l,r = unpack(b);      Unpacks byte b, returning the left (or high) 
                        nybble in l, and the right (or low) nybble in r.

  d = dupl(b);          Duplicates the low nybble of byte b into the
                        high nybble and returns the new byte in d.

                        Note: Executes function pack() with b as both
                        arguments.

  d = swap(b);          Swaps the left (or high) and right (or low) 
                        nybbles of byte b and returns the new byte in d.

                        Note: Executes function rotl() with the arguments
                        b and 4.




  c,d,e = func(a,&d);   Stores the input value a and the address of d 
                        in memory.

                        Returns three bytes read from memory.

                        Note: Writes argument a to variable arg0,
                        the address of d to variables adr0 and adr1,
                        and returns the values of variables var0,
                        var1, and var2.

Note: This library expects the following external variables to be defined:

  temp0:                Temporary Variable