bitstring.3

source code of crond

.\" Copyright (c) 1989 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Paul Vixie.
.\"
.\" Redistribution and use in source and binary forms are permitted
.\" provided that the above copyright notice and this paragraph are
.\" duplicated in all such forms and that any documentation,
.\" advertising materials, and other materials related to such
.\" distribution and use acknowledge that the software was developed
.\" by the University of California, Berkeley.  The name of the
.\" University may not be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.\"	@(#)bitstring.3	5.1 (Berkeley) 12/13/89
.\"
.TH BITSTRING 3  "December 13, 1989"
.UC 4
.SH NAME
bit_alloc, bit_clear, bit_decl, bit_ffs, bit_nclear, bit_nset,
bit_set, bitstr_size, bit_test \- bit-string manipulation macros
.SH SYNOPSIS
.ft B
.nf
#include <bitstring.h>

name = bit_alloc(nbits)
bitstr_t *name;
int nbits;

bit_decl(name, nbits)
bitstr_t name;
int nbits;

bit_clear(name, bit)
bitstr_t name;
int bit;

bit_ffc(name, nbits, value)
bitstr_t name;
int nbits, *value;

bit_ffs(name, nbits, value)
bitstr_t name;
int nbits, *value;

bit_nclear(name, start, stop)
bitstr_t name;
int start, stop;

bit_nset(name, start, stop)
bitstr_t name;
int start, stop;

bit_set(name, bit)
bitstr_t name;
int bit;

bitstr_size(nbits)
int nbits;

bit_test(name, bit)
bitstr_t name;
int bit;
.fi
.ft R
.SH DESCRIPTION
These macros operate on strings of bits.
.PP
.I Bit_alloc
returns a pointer of type
.I bitstr_t\ *
to sufficient space to store
.I nbits
bits, or NULL if no space is available.
.PP
.I Bit_decl
is a macro for allocating sufficient space to store
.I nbits
bits on the stack.
.PP
.I Bitstr_size
returns the number of elements of type
.I bitstr_t
necessary to store
.I nbits
bits.
This is useful for copying bit strings.
.PP
.I Bit_clear
and
.I bit_set
clear or set the zero-based numbered bit
.IR bit ,
in the bit string
.IR name .
.PP
.I Bit_nset
and
.I bit_nclear
set or clear the zero-based numbered bits from
.I start
to
.I stop
in the bit string
.IR name .
.PP
.I Bit_test
evaluates to zero if the zero-based numbered bit
.I bit
of bit string
.I name
is set, and non-zero otherwise.
.PP
.I Bit_ffs
sets
.I *value
to the zero-based number of the first bit set in the array of
.I nbits
bits referenced by
.IR name .
If no bits are set,
.I *value
is set to -1.
.PP
.I Bit_ffc
sets
.I *value
to the zero-based number of the first bit not set in the array of
.I nbits
bits referenced by
.IR name .
If all bits are set,
.I value
is set to -1.
.SH EXAMPLE
.nf
.in +5
#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);
	}
}
.fi
.SH "SEE ALSO"
malloc(3)