EN JA
BITSTRING(3)
BITSTRING(3) FreeBSD Library Functions Manual BITSTRING(3)

NAME

bit_alloc, bit_clear, bit_decl, bit_ffs, bit_nclear, bit_nset, bit_set, bitstr_size, bit_testbit-string manipulation macros

SYNOPSIS

#include < bitstring.h>

bitstr_t *
bit_alloc( int nbits);

void
bit_decl( bitstr_t *name, int nbits);

void
bit_clear( bitstr_t *name, int bit);

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

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

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

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

void
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 through 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 arguments to these macros are evaluated only once and may safely have side effects.

EXAMPLES

#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.
July 19, 1993 FreeBSD