.\"	$OpenBSD: bitstring.3,v 1.12 2005/03/07 22:10:28 jmc Exp $
.\"	$NetBSD: bitstring.3,v 1.4 1994/11/30 15:24:31 jtc Exp $
.\"
.\" Copyright (c) 1989, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Paul Vixie.
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.\"     @(#)bitstring.3	8.1 (Berkeley) 7/19/93
.\"
.Dd July 19, 1993
.Dt BITSTRING 3
.Os
.Sh NAME
.Nm bit_alloc ,
.Nm bit_clear ,
.Nm bit_decl ,
.Nm bit_ffc ,
.Nm bit_ffs ,
.Nm bit_nclear ,
.Nm bit_nset ,
.Nm bit_set ,
.Nm bitstr_size ,
.Nm bit_test
.Nd bit-string manipulation macros
.Sh SYNOPSIS
.Fd #include <bitstring.h>
.Ft bitstr_t *
.Fn bit_alloc "int nbits"
.Fn bit_clear "bit_str name" "int bit"
.Fn bit_decl "bit_str name" "int nbits"
.Fn bit_ffc "bit_str name" "int nbits" "int *value"
.Fn bit_ffs "bit_str name" "int nbits" "int *value"
.Fn bit_nclear "bit_str name" "int start" "int stop"
.Fn bit_nset "bit_str name" "int start" "int stop"
.Fn bit_set "bit_str name" "int bit"
.Fn bitstr_size "int nbits"
.Fn bit_test "bit_str name" "int bit"
.Sh DESCRIPTION
These macros operate on strings of bits.
.Pp
The
.Fn bit_alloc
macro returns a pointer of type
.Li "bitstr_t *"
to sufficient space to store
.Fa nbits
bits, or
.Dv NULL
if no space is available.
.Pp
The
.Fn bit_decl
macro allocates sufficient space to store
.Fa nbits
bits on the stack.
.Pp
The
.Fn bitstr_size
macro returns the number of elements of type
.Li bitstr_t
necessary to store
.Fa nbits
bits.
This is useful for copying bit strings.
.Pp
The
.Fn bit_clear
and
.Fn bit_set
macros clear or set the zero-based numbered bit
.Fa bit ,
in the bit string
.Ar name .
.Pp
The
.Fn bit_nclear
and
.Fn bit_nset
macros clear or set the zero-based numbered bits from
.Fa start
to
.Fa stop
in the bit string
.Ar name .
.Pp
The
.Fn bit_test
macro evaluates to non-zero if the zero-based numbered bit
.Fa bit
of bit string
.Fa name
is set, and zero otherwise.
.Pp
The
.Fn bit_ffs
macro 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
.Fn bit_ffc
macro 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 arguments to these 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
.Sh HISTORY
The
.Nm bitstring
functions first appeared in
.Bx 4.4 .