bitstring.3

早期freebsd实现

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.\"     @(#)bitstring.3	8.1 (Berkeley) 7/19/93
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.Dd July 19, 1993
.Dt BITSTRING 3
.Os BSD 4
.Sh NAME
.Nm bit_alloc ,
.Nm bit_clear ,
.Nm bit_decl ,
.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_decl "bit_str name" "int nbits"
.Fn bit_clear "bit_str name" "int bit"
.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 macro
.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.
.Pp
The macro
.Fn bit_decl
allocates sufficient space to store
.Fa nbits
bits on the stack.
.Pp
The macro
.Fn bitstr_size
returns the number of elements of type
.Fa bitstr_t
necessary to store
.Fa nbits
bits.
This is useful for copying bit strings.
.Pp
The macros
.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
macros
set or clear 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 macro
.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 arguments to these macros are evaluated only once and may safely
have side effects.
.Sh EXAMPLE
.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 4.4BSD.