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FreeBSD 11.0 - man page for bit_ffc (freebsd section 3)

BITSTRING(3)						   BSD Library Functions Manual 					      BITSTRING(3)

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); 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 refer- enced 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 ref- erenced 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.
BSD
July 19, 1993 BSD