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Manual Pages  — BITSTRING

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

CONTENTS

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

malloc(3), bitset(9)

HISTORY

The bitstring functions first appeared in BSD 4.4 .

BITSTRING (3) May 23, 2016

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