/*
	The bitstring header file

	Note: the specifications for the procedures and macros are placed
	in this header, because this interface is what a user of the
	bitstring module sees.  They may not even have access to the
	implementation.

    General Assumptions:
	The bits of a bitstring x are numbered in string order, that is
		0, 1, 2, ..., bits_length(x)-1

	The length of a bitstring may vary.

	An individual bit is an unsigned int of value 0 or 1.  If something
	other than 0 or 1 is supplied by the user as a bit, only the least
	significant bit is used.
*/


/*
    A bitstring is of type bits.  

    Invariant: at present we only permit fixed length bitstrings of 
	as many bits as are in an unsigned int.
*/
typedef unsigned int bits;

#define bits_length(x)  ( (int) (8*sizeof(bits)))
/*
    Get the length of a bitstring

    Pre: none
    Post: bits_length(x) is the number of bits in the bitstring x
    Side Effects: none
*/

extern unsigned int bits_get (bits x, int i);
/*
    Pre: 
	0 <= i < bits_length(x)
    Post:
 	bits_get(x,i) is the value of bit i of x
    Side effects:
	none
*/


extern bits bits_put (bits x, int i, unsigned int v);
/*
    Pre:
	0 <= i < bits_length(x)
    Post:
	bits_put(x, i, v) is the same as x except that bit i is set 
	to the same value as bit 0 of v.
    Side effects:
	none
*/

extern void bits_printf (bits x);
/*
    Pre:
	none
    Post:
	none
    Side Effects:
	the bits of x are printed on stdout in string order,
	0, 1, 2, ...
*/

#define bits_from_int(x) (x)
/*
    Convert an int into a bitstring

    Pre: none
    Post: bits_from_int(x) is a bitstring that contains the bits of x
	  ordered from least significant first to most significant last.
    Side Effects: none
*/