NAME
bit_alloc,
bit_clear, bit_count,
bit_decl, bit_ffc,
bit_ffs, bit_ffc_at,
bit_ffs_at, bit_nclear,
bit_nset, bit_set,
bit_test, bitstr_size
— bit-string manipulation
functions and 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_count(bitstr_t
*name, int count,
int nbits,
int *value);
void
bit_ffc(bitstr_t
*name, int nbits,
int *value);
void
bit_ffs(bitstr_t
*name, int nbits,
int *value);
void
bit_ffc_at(bitstr_t
*name, int start,
int nbits,
int *value);
void
bit_ffs_at(bitstr_t
*name, int start,
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 function
bit_alloc()
returns a pointer of type “bitstr_t *”
to sufficient space to store nbits bits, or
NULL if no space is available. If successful, the
returned bit string is initialized with all bits cleared.
The macro
bit_decl()
declares a bit string with sufficient space to store
nbits bits. bit_decl() may be
used to include statically sized bit strings in structure definitions or to
create bit strings on the stack. Users of this macro are responsible for
initialization of the bit string, typically via a global initialization of
the containing struct or use of the bit_nset() or
bin_nclear()
functions.
The macro
bitstr_size()
returns the number of bytes necessary to store nbits
bits. This is useful for copying bit strings.
The functions
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()
functions set or clear the zero-based numbered bits from
start through stop in the bit
string name.
The
bit_test()
function evaluates to non-zero if the zero-based numbered bit
bit of bit string name is set,
and zero otherwise.
The function
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
bit_ffs()
function 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 function
bit_ffc_at()
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,
at or after the zero-based bit index start. If all
bits at or after start are set, the location
referenced by value is set to -1.
The
bit_ffs_at()
function 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,
at or after the zero-based bit index start. If no bits
are set after start, the location referenced by
value is set to -1.
The
bit_count()
function stores in the location referenced by value
the number of bits set in the array of nbits bits
referenced by name, at or after the zero-based bit
index start.
The arguments in bit string 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
HISTORY
The bitstring functions first appeared in
4.4BSD.