1b82e02f4d
Add a bit_count function, which efficiently counts the number of bits set in a bitstring. sys/sys/bitstring.h tests/sys/sys/bitstring_test.c share/man/man3/bitstring.3 Add bit_alloc sys/kern/subr_unit.c Use bit_count instead of a naive counting loop in check_unrhdr, used when INVARIANTS are enabled. The userland test runs about 6x faster in a generic build, or 8.5x faster when built for Nehalem, which has the POPCNT instruction. sys/sys/param.h Bump __FreeBSD_version due to the addition of bit_alloc UPDATING Add a note about the ABI incompatibility of the bitstring(3) changes, as suggested by lidl. Suggested by: gibbs Reviewed by: gibbs, ngie MFC after: 9 days X-MFC-With: 299090, 300538 Relnotes: yes Sponsored by: Spectra Logic Corp Differential Revision: https://reviews.freebsd.org/D6255
278 lines
7.5 KiB
Groff
278 lines
7.5 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Paul Vixie.
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" Copyright (c) 2014,2016 Spectra Logic Corporation
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions, and the following disclaimer,
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.\" without modification.
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.\" 2. Redistributions in binary form must reproduce at minimum a disclaimer
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.\" substantially similar to the "NO WARRANTY" disclaimer below
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.\" ("Disclaimer") and any redistribution must be conditioned upon
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.\" including a substantially similar Disclaimer requirement for further
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.\" binary redistribution.
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.\"
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.\" NO WARRANTY
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR
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.\" A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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.\" HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
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.\" IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGES.
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.\"
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.\" @(#)bitstring.3 8.1 (Berkeley) 7/19/93
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.\" $FreeBSD$
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.\"
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.Dd May 23, 2016
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.Dt BITSTRING 3
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.Os
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.Sh NAME
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.Nm bit_alloc ,
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.Nm bit_clear ,
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.Nm bit_count ,
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.Nm bit_decl ,
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.Nm bit_ffc ,
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.Nm bit_ffs ,
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.Nm bit_ffc_at ,
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.Nm bit_ffs_at ,
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.Nm bit_nclear ,
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.Nm bit_nset ,
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.Nm bit_set ,
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.Nm bit_test ,
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.Nm bitstr_size
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.Nd bit-string manipulation functions and macros
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.Sh SYNOPSIS
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.In bitstring.h
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.Ft bitstr_t *
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.Fn bit_alloc "int nbits"
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.Ft void
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.Fn bit_decl "bitstr_t *name" "int nbits"
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.Ft void
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.Fn bit_clear "bitstr_t *name" "int bit"
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.Ft void
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.Fn bit_count "bitstr_t *name" "int count" "int nbits" "int *value"
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.Ft void
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.Fn bit_ffc "bitstr_t *name" "int nbits" "int *value"
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.Ft void
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.Fn bit_ffs "bitstr_t *name" "int nbits" "int *value"
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.Ft void
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.Fn bit_ffc_at "bitstr_t *name" "int start" "int nbits" "int *value"
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.Ft void
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.Fn bit_ffs_at "bitstr_t *name" "int start" "int nbits" "int *value"
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.Ft void
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.Fn bit_nclear "bitstr_t *name" "int start" "int stop"
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.Ft void
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.Fn bit_nset "bitstr_t *name" "int start" "int stop"
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.Ft void
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.Fn bit_set "bitstr_t *name" "int bit"
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.Ft int
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.Fn bitstr_size "int nbits"
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.Ft int
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.Fn bit_test "bitstr_t *name" "int bit"
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.Sh DESCRIPTION
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These macros operate on strings of bits.
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.Pp
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The function
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.Fn bit_alloc
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returns a pointer of type
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.Dq Fa "bitstr_t *"
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to sufficient space to store
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.Fa nbits
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bits, or
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.Dv NULL
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if no space is available.
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If successful, the returned bit string is initialized with all bits cleared.
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.Pp
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The macro
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.Fn bit_decl
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declares a bit string with sufficient space to store
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.Fa nbits
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bits.
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.Fn bit_decl
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may be used to include statically sized bit strings in structure
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definitions or to create bit strings on the stack.
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Users of this macro are responsible for initialization of the bit string,
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typically via a global initialization of the containing struct or use of the
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.Fn bit_nset
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or
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.Fn bin_nclear
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functions.
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.Pp
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The macro
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.Fn bitstr_size
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returns the number of bytes necessary to store
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.Fa nbits
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bits.
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This is useful for copying bit strings.
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.Pp
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The functions
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.Fn bit_clear
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and
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.Fn bit_set
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clear or set the zero-based numbered bit
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.Fa bit ,
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in the bit string
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.Ar name .
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.Pp
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The
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.Fn bit_nset
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and
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.Fn bit_nclear
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functions
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set or clear the zero-based numbered bits from
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.Fa start
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through
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.Fa stop
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in the bit string
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.Ar name .
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.Pp
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The
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.Fn bit_test
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function
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evaluates to non-zero if the zero-based numbered bit
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.Fa bit
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of bit string
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.Fa name
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is set, and zero otherwise.
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.Pp
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The function
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.Fn bit_ffc
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stores in the location referenced by
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.Fa value
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the zero-based number of the first bit not set in the array of
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.Fa nbits
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bits referenced by
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.Fa name .
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If all bits are set, the location referenced by
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.Fa value
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is set to \-1.
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.Pp
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The
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.Fn bit_ffs
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function
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stores in the location referenced by
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.Fa value
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the zero-based number of the first bit set in the array of
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.Fa nbits
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bits referenced by
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.Fa name .
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If no bits are set, the location referenced by
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.Fa value
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is set to \-1.
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.Pp
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The function
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.Fn bit_ffc_at
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stores in the location referenced by
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.Fa value
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the zero-based number of the first bit not set in the array of
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.Fa nbits
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bits referenced by
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.Fa name ,
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at or after the zero-based bit index
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.Fa start .
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If all bits at or after
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.Fa start
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are set, the location referenced by
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.Fa value
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is set to \-1.
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.Pp
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The
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.Fn bit_ffs_at
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function
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stores in the location referenced by
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.Fa value
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the zero-based number of the first bit set in the array of
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.Fa nbits
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bits referenced by
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.Fa name ,
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at or after the zero-based bit index
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.Fa start .
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If no bits are set after
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.Fa start ,
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the location referenced by
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.Fa value
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is set to \-1.
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.Pp
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The
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.Fn bit_count
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function stores in the location referenced by
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.Fa value
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the number of bits set in the array of
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.Fa nbits
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bits referenced by
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.Fa name ,
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at or after the zero-based bit index
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.Fa start .
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.Pp
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The arguments in bit string macros are evaluated only once and may safely
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have side effects.
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.Sh EXAMPLES
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.Bd -literal -offset indent
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#include <limits.h>
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#include <bitstring.h>
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\&...
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#define LPR_BUSY_BIT 0
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#define LPR_FORMAT_BIT 1
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#define LPR_DOWNLOAD_BIT 2
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\&...
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#define LPR_AVAILABLE_BIT 9
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#define LPR_MAX_BITS 10
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make_lpr_available()
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{
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bitstr_t bit_decl(bitlist, LPR_MAX_BITS);
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...
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bit_nclear(bitlist, 0, LPR_MAX_BITS - 1);
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...
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if (!bit_test(bitlist, LPR_BUSY_BIT)) {
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bit_clear(bitlist, LPR_FORMAT_BIT);
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bit_clear(bitlist, LPR_DOWNLOAD_BIT);
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bit_set(bitlist, LPR_AVAILABLE_BIT);
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}
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}
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.Ed
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.Sh SEE ALSO
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.Xr malloc 3 ,
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.Xr bitset 9
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.Sh HISTORY
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The
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.Nm bitstring
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functions first appeared in
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.Bx 4.4 .
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