NAME

bit_alloc, bit_clear, bit_decl, bit_ffs, bit_nclear, bit_nset, bit_set, bitstr_size, bit_test — bit-string manipulation macros

SYNOPSIS

#include <bitstring.h>

bitstr_t *
bit_alloc(int nbits);

bit_decl(bitstr_t *name, int nbits);

bit_clear(bitstr_t *name, int bit);

bit_ffc(bitstr_t *name, int nbits, int *value);

bit_ffs(bitstr_t *name, int nbits, int *value);

bit_nclear(bitstr_t *name, int start, int stop);

bit_nset(bitstr_t *name, int start, int stop);

bit_set(bitstr_t *name, int bit);

int
bitstr_size(int nbits);

int
bit_test(bitstr_t *name, int bit);

DESCRIPTION

These macros operate on strings of bits.

The macro bit_alloc() returns a pointer of type “bitstr_t *” to sufficient space to store nbits bits, or NULL if no space is available.

The macro bit_decl() allocates sufficient space to store nbits bits on the stack.

The macro bitstr_size() returns the number of elements of type bitstr_t necessary to store nbits bits. This is useful for copying bit strings.

The macros bit_clear() and bit_set() clear or set the zero-based numbered bit bit, in the bit string name.

The bit_nset() and bit_nclear() macros set or clear the zero-based numbered bits from start to stop in the bit string name.

The bit_test() macro evaluates to non-zero if the zero-based numbered bit bit of bit string name is set, and zero otherwise.

The bit_ffs() macro stores in the location referenced by value the zero-based number of the first bit set in the array of nbits bits referenced by name. If no bits are set, the location referenced by value is set to -1.

The macro bit_ffc() stores in the location referenced by value the zero-based number of the first bit not set in the array of nbits bits referenced by name. If all bits are set, the location referenced by value is set to -1.

The macros bit_clear(), bit_set() and bit_test() will evaluate the bit argument more than once, so avoid using pre- or post-, increment or decrement. The arguments to the other macros are evaluated only once and may safely have side effects.

EXAMPLE

#include <limits.h>
#include <bitstring.h>

...
#define	LPR_BUSY_BIT		0
#define	LPR_FORMAT_BIT		1
#define	LPR_DOWNLOAD_BIT	2
...
#define	LPR_AVAILABLE_BIT	9
#define	LPR_MAX_BITS		10

make_lpr_available()
{
	bitstr_t bit_decl(bitlist, LPR_MAX_BITS);
	...
	bit_nclear(bitlist, 0, LPR_MAX_BITS - 1);
	...
	if (!bit_test(bitlist, LPR_BUSY_BIT)) {
		bit_clear(bitlist, LPR_FORMAT_BIT);
		bit_clear(bitlist, LPR_DOWNLOAD_BIT);
		bit_set(bitlist, LPR_AVAILABLE_BIT);
	}
}

SEE ALSO

malloc(3)

HISTORY

The bitstring functions first appeared in 4.4BSD.