xref: /freebsd/share/man/man3/bitstring.3 (revision 1b82e02f4d91dc0942e754fa6c08042537f13980)

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.Dd May 23, 2016
.Dt BITSTRING 3
.Os
.Sh NAME
.Nm bit_alloc ,
.Nm bit_clear ,
.Nm bit_count ,
.Nm bit_decl ,
.Nm bit_ffc ,
.Nm bit_ffs ,
.Nm bit_ffc_at ,
.Nm bit_ffs_at ,
.Nm bit_nclear ,
.Nm bit_nset ,
.Nm bit_set ,
.Nm bit_test ,
.Nm bitstr_size
.Nd bit-string manipulation functions and macros
.Sh SYNOPSIS
.In bitstring.h
.Ft bitstr_t *
.Fn bit_alloc "int nbits"
.Ft void
.Fn bit_decl "bitstr_t *name" "int nbits"
.Ft void
.Fn bit_clear "bitstr_t *name" "int bit"
.Ft void
.Fn bit_count "bitstr_t *name" "int count" "int nbits" "int *value"
.Ft void
.Fn bit_ffc "bitstr_t *name" "int nbits" "int *value"
.Ft void
.Fn bit_ffs "bitstr_t *name" "int nbits" "int *value"
.Ft void
.Fn bit_ffc_at "bitstr_t *name" "int start" "int nbits" "int *value"
.Ft void
.Fn bit_ffs_at "bitstr_t *name" "int start" "int nbits" "int *value"
.Ft void
.Fn bit_nclear "bitstr_t *name" "int start" "int stop"
.Ft void
.Fn bit_nset "bitstr_t *name" "int start" "int stop"
.Ft void
.Fn bit_set "bitstr_t *name" "int bit"
.Ft int
.Fn bitstr_size "int nbits"
.Ft int
.Fn bit_test "bitstr_t *name" "int bit"
.Sh DESCRIPTION
These macros operate on strings of bits.
.Pp
The function
.Fn bit_alloc
returns a pointer of type
.Dq Fa "bitstr_t *"
to sufficient space to store
.Fa nbits
bits, or
.Dv NULL
if no space is available.
If successful, the returned bit string is initialized with all bits cleared.
.Pp
The macro
.Fn bit_decl
declares a bit string with sufficient space to store
.Fa nbits
bits.
.Fn 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
.Fn bit_nset
or
.Fn bin_nclear
functions.
.Pp
The macro
.Fn bitstr_size
returns the number of bytes necessary to store
.Fa nbits
bits.
This is useful for copying bit strings.
.Pp
The functions
.Fn bit_clear
and
.Fn bit_set
clear or set the zero-based numbered bit
.Fa bit ,
in the bit string
.Ar name .
.Pp
The
.Fn bit_nset
and
.Fn bit_nclear
functions
set or clear the zero-based numbered bits from
.Fa start
through
.Fa stop
in the bit string
.Ar name .
.Pp
The
.Fn bit_test
function
evaluates to non-zero if the zero-based numbered bit
.Fa bit
of bit string
.Fa name
is set, and zero otherwise.
.Pp
The function
.Fn bit_ffc
stores in the location referenced by
.Fa value
the zero-based number of the first bit not set in the array of
.Fa nbits
bits referenced by
.Fa name .
If all bits are set, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffs
function
stores in the location referenced by
.Fa value
the zero-based number of the first bit set in the array of
.Fa nbits
bits referenced by
.Fa name .
If no bits are set, the location referenced by
.Fa value
is set to \-1.
.Pp
The function
.Fn bit_ffc_at
stores in the location referenced by
.Fa value
the zero-based number of the first bit not set in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
If all bits at or after
.Fa start
are set, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffs_at
function
stores in the location referenced by
.Fa value
the zero-based number of the first bit set in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
If no bits are set after
.Fa start ,
the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_count
function stores in the location referenced by
.Fa value
the number of bits set in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
.Pp
The arguments in bit string macros are evaluated only once and may safely
have side effects.
.Sh EXAMPLES
.Bd -literal -offset indent
#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);
	}
}
.Ed
.Sh SEE ALSO
.Xr malloc 3 ,
.Xr bitset 9
.Sh HISTORY
The
.Nm bitstring
functions first appeared in
.Bx 4.4 .