.\" Copyright (c) 2015 Conrad Meyer <cem@FreeBSD.org>
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.Dd September 20, 2021
.Dt BITSET 9
.Os
.Sh NAME
.Nm bitset(9)
\(em
.Nm BITSET_DEFINE ,
.Nm BITSET_T_INITIALIZER ,
.Nm BITSET_FSET ,
.Nm BIT_CLR ,
.Nm BIT_COPY ,
.Nm BIT_ISSET ,
.Nm BIT_SET ,
.Nm BIT_ZERO ,
.Nm BIT_FILL ,
.Nm BIT_SETOF ,
.Nm BIT_EMPTY ,
.Nm BIT_ISFULLSET ,
.Nm BIT_FFS ,
.Nm BIT_FFS_AT ,
.Nm BIT_FLS ,
.Nm BIT_FOREACH_ISSET ,
.Nm BIT_FOREACH_ISCLR ,
.Nm BIT_COUNT ,
.Nm BIT_SUBSET ,
.Nm BIT_OVERLAP ,
.Nm BIT_CMP ,
.Nm BIT_OR ,
.Nm BIT_OR2 ,
.Nm BIT_AND ,
.Nm BIT_AND2 ,
.Nm BIT_ANDNOT ,
.Nm BIT_ANDNOT2 ,
.Nm BIT_XOR ,
.Nm BIT_XOR2 ,
.Nm BIT_CLR_ATOMIC ,
.Nm BIT_SET_ATOMIC ,
.Nm BIT_SET_ATOMIC_ACQ ,
.Nm BIT_TEST_SET_ATOMIC ,
.Nm BIT_TEST_CLR_ATOMIC ,
.Nm BIT_AND_ATOMIC ,
.Nm BIT_OR_ATOMIC ,
.Nm BIT_COPY_STORE_REL
.Nd bitset manipulation macros
.Sh SYNOPSIS
.In sys/_bitset.h
.In sys/bitset.h
.\"
.Fn BITSET_DEFINE "STRUCTNAME" "const SETSIZE"
.Fn BITSET_T_INITIALIZER "ARRAY_CONTENTS"
.Fn BITSET_FSET "N_WORDS"
.\"
.Fn BIT_CLR "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Fn BIT_COPY "const SETSIZE" "struct STRUCTNAME *from" "struct STRUCTNAME *to"
.Ft bool
.Fn BIT_ISSET "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Fn BIT_SET "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Fn BIT_ZERO "const SETSIZE" "struct STRUCTNAME *bitset"
.Fn BIT_FILL "const SETSIZE" "struct STRUCTNAME *bitset"
.Fn BIT_SETOF "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Ft bool
.Fn BIT_EMPTY "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft bool
.Fn BIT_ISFULLSET "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft long
.Fn BIT_FFS "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft long
.Fn BIT_FFS_AT "const SETSIZE" "struct STRUCTNAME *bitset" "long start"
.Ft long
.Fn BIT_FLS "const SETSIZE" "struct STRUCTNAME *bitset"
.Fo BIT_FOREACH_ISSET
.Fa "const SETSIZE"
.Fa "size_t bit"
.Fa "const struct STRUCTNAME *bitset"
.Fc
.Fo BIT_FOREACH_ISCLR
.Fa "const SETSIZE"
.Fa "size_t bit"
.Fa "const struct STRUCTNAME *bitset"
.Fc
.Ft long
.Fn BIT_COUNT "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft bool
.Fo BIT_SUBSET
.Fa "const SETSIZE" "struct STRUCTNAME *haystack" "struct STRUCTNAME *needle"
.Fc
.Ft bool
.Fo BIT_OVERLAP
.Fa "const SETSIZE" "struct STRUCTNAME *bitset1" "struct STRUCTNAME *bitset2"
.Fc
.Ft bool
.Fo BIT_CMP
.Fa "const SETSIZE" "struct STRUCTNAME *bitset1" "struct STRUCTNAME *bitset2"
.Fc
.Fn BIT_OR "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fo BIT_OR2
.Fa "const SETSIZE"
.Fa "struct STRUCTNAME *dst"
.Fa "struct STRUCTNAME *src1"
.Fa "struct STRUCTNAME *src2"
.Fc
.Fn BIT_AND "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fo BIT_AND2
.Fa "const SETSIZE"
.Fa "struct STRUCTNAME *dst"
.Fa "struct STRUCTNAME *src1"
.Fa "struct STRUCTNAME *src2"
.Fc
.Fn BIT_ANDNOT "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fo BIT_ANDNOT2
.Fa "const SETSIZE"
.Fa "struct STRUCTNAME *dst"
.Fa "struct STRUCTNAME *src1"
.Fa "struct STRUCTNAME *src2"
.Fc
.Fn BIT_XOR "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fo BIT_XOR2
.Fa "const SETSIZE"
.Fa "struct STRUCTNAME *dst"
.Fa "struct STRUCTNAME *src1"
.Fa "struct STRUCTNAME *src2"
.Fc
.\"
.Fn BIT_CLR_ATOMIC "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Fn BIT_SET_ATOMIC "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Fn BIT_SET_ATOMIC_ACQ "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Ft bool
.Fn BIT_TEST_SET_ATOMIC "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.Ft bool
.Fn BIT_TEST_CLR_ATOMIC "const SETSIZE" "size_t bit" "struct STRUCTNAME *bitset"
.\"
.Fo BIT_AND_ATOMIC
.Fa "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fc
.Fo BIT_OR_ATOMIC
.Fa "const SETSIZE" "struct STRUCTNAME *dst" "struct STRUCTNAME *src"
.Fc
.Fo BIT_COPY_STORE_REL
.Fa "const SETSIZE" "struct STRUCTNAME *from" "struct STRUCTNAME *to"
.Fc
.Fd #define _WANT_FREEBSD_BITSET
.Sh DESCRIPTION
The
.Nm
family of macros provide a flexible and efficient bitset implementation if the
maximum size of the set is known at compilation.
Throughout this manual page, the name
.Fa SETSIZE
refers to the size of the bitset in bits.
Individual bits in bitsets are referenced with indices zero through
.Fa SETSIZE - 1 .
One example use of
.In sys/bitset.h
is
.In sys/cpuset.h .
.Pp
These macros are meant to be used in the kernel and are visible if
.Dv _KERNEL is defined when
.In sys/_bitset.h
or
.In sys/bitset.h
are included in a program.
Userland programs must define 
.Dv _WANT_FREEBSD_BITSET
before including these files to make the macros visible.
.Pp
The
.Fn BITSET_DEFINE
macro defines a bitset struct
.Fa STRUCTNAME
with room to represent
.Fa SETSIZE
bits.
.Pp
The
.Fn BITSET_T_INITIALIZER
macro allows one to initialize a bitset struct with a compile time literal
value.
.Pp
The
.Fn BITSET_FSET
macro generates a compile time literal, usable by
.Fn BITSET_T_INITIALIZER ,
representing a full bitset (all bits set).
For examples of
.Fn BITSET_T_INITIALIZER
and
.Fn BITSET_FSET
usage, see the
.Sx BITSET_T_INITIALIZER EXAMPLE
section.
The
.Fa N_WORDS
parameter to
.Fn BITSET_FSET
should be:
.Bd -literal -offset indent
__bitset_words(SETSIZE)
.Ed
.Pp
The
.Fn BIT_CLR
macro clears bit
.Fa bit
in the bitset pointed to by
.Fa bitset .
The
.Fn BIT_CLR_ATOMIC
macro is identical, but the bit is cleared atomically.
The
.Fn BIT_TEST_CLR_ATOMIC
macro atomically clears the bit and returns whether it was set.
.Pp
The
.Fn BIT_COPY
macro copies the contents of the bitset
.Fa from
to the bitset
.Fa to .
.Fn BIT_COPY_STORE_REL
is similar, but copies component machine words from
.Fa from
and writes them to
.Fa to
with atomic store with release semantics.
(That is, if
.Fa to
is composed of multiple machine words,
.Fn BIT_COPY_STORE_REL
performs multiple individually atomic operations.)
.Pp
The
.Fn BIT_ISSET
macro returns
.Dv true
if the bit
.Fa bit
in the bitset pointed to by
.Fa bitset
is set.
.Pp
The
.Fn BIT_SET
macro sets bit
.Fa bit
in the bitset pointed to by
.Fa bitset .
The
.Fn BIT_SET_ATOMIC
macro is identical, but the bit is set atomically.
The
.Fn BIT_SET_ATOMIC_ACQ
macro sets the bit with acquire semantics.
The
.Fn BIT_TEST_SET_ATOMIC
macro atomically sets the bit and returns whether it was set.
.Pp
The
.Fn BIT_ZERO
macro clears all bits in
.Fa bitset .
.Pp
The
.Fn BIT_FILL
macro sets all bits in
.Fa bitset .
.Pp
The
.Fn BIT_SETOF
macro clears all bits in
.Fa bitset
before setting only bit
.Fa bit .
.Pp
The
.Fn BIT_EMPTY
macro returns
.Dv true
if
.Fa bitset
is empty.
.Pp
The
.Fn BIT_ISFULLSET
macro returns
.Dv true
if
.Fa bitset
is full (all bits set).
.Pp
The
.Fn BIT_FFS
macro returns the 1-index of the first (lowest) set bit in
.Fa bitset ,
or zero if
.Fa bitset
is empty.
Like with
.Xr ffs 3 ,
to use the non-zero result of
.Fn BIT_FFS
as a
.Fa bit
index parameter to any other
.Nm
macro, you must subtract one from the result.
.Pp
The
.Fn BIT_FFS_AT
macro returns the 1-index of the first (lowest) set bit in
.Fa bitset ,
which is greater than the given 1-indexed
.Fa start ,
or zero if no bits in
.Fa bitset
greater than
.Fa start
are set.
.Pp
The
.Fn BIT_FLS
macro returns the 1-index of the last (highest) set bit in
.Fa bitset ,
or zero if
.Fa bitset
is empty.
Like with
.Xr fls 3 ,
to use the non-zero result of
.Fn BIT_FLS
as a
.Fa bit
index parameter to any other
.Nm
macro, you must subtract one from the result.
.Pp
The
.Fn BIT_FOREACH_ISSET
macro can be used to iterate over all set bits in
.Fa bitset .
The index variable
.Fa bit
must have been declared with type
.Ft int ,
and upon each iteration
.Fa bit
is set to the index of successive set bits.
The value of
.Fa bit
after the loop terminates is undefined.
Similarly,
.Fn BIT_FOREACH_ISCLR
iterates over all clear bits in
.Fa bitset .
In the loop body, the currently indexed bit may be set or cleared.
However, setting or clearing bits other than the currently indexed
bit does not guarantee that they will or will not be returned in
subsequent iterations of the same loop.
.Pp
The
.Fn BIT_COUNT
macro returns the total number of set bits in
.Fa bitset .
.Pp
The
.Fn BIT_SUBSET
macro returns
.Dv true
if
.Fa needle
is a subset of
.Fa haystack .
.Pp
The
.Fn BIT_OVERLAP
macro returns
.Dv true
if
.Fa bitset1
and
.Fa bitset2
have any common bits.
(That is, if
.Fa bitset1
AND
.Fa bitset2
is not the empty set.)
.Pp
The
.Fn BIT_CMP
macro returns
.Dv true
if
.Fa bitset1
is NOT equal to
.Fa bitset2 .
.Pp
The
.Fn BIT_OR
macro sets bits present in
.Fa src
in
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
|=
.Fa src . )
.Fn BIT_OR_ATOMIC
is similar, but sets bits in the component machine words in
.Fa dst
atomically.
(That is, if
.Fa dst
is composed of multiple machine words,
.Fn BIT_OR_ATOMIC
performs multiple individually atomic operations.)
.Pp
The
.Fn BIT_OR2
macro computes
.Fa src1
bitwise or
.Fa src2
and assigns the result to
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
=
.Fa src1
|
.Fa src2 . )
.Pp
The
.Fn BIT_AND
macro clears bits absent from
.Fa src
from
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
&=
.Fa src . )
.Fn BIT_AND_ATOMIC
is similar, with the same atomic semantics as
.Fn BIT_OR_ATOMIC .
.Pp
The
.Fn BIT_AND2
macro computes
.Fa src1
bitwise and
.Fa src2
and assigns the result to
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
=
.Fa src1
&
.Fa src2 . )
.Pp
The
.Fn BIT_ANDNOT
macro clears bits set in
.Fa src
from
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
&=
.Fa ~ src . )
.Pp
The
.Fn BIT_ANDNOT2
macro computes
.Fa src1
bitwise and not
.Fa src2
and assigns the result to
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
=
.Fa src1
& ~
.Fa src2 . )
.Pp
The
.Fn BIT_XOR
macro toggles bits set in
.Fa src
in
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
^=
.Fa src . )
.Pp
The
.Fn BIT_XOR2
macro computes
.Fa src1
bitwise exclusive or
.Fa src2
and assigns the result to
.Fa dst .
(It is the
.Nm
equivalent of the scalar:
.Fa dst
=
.Fa src1
^
.Fa src2 . )
.Sh BITSET_T_INITIALIZER EXAMPLE
.Bd -literal
BITSET_DEFINE(_myset, MYSETSIZE);

struct _myset myset;

/* Initialize myset to filled (all bits set) */
myset = BITSET_T_INITIALIZER(BITSET_FSET(__bitset_words(MYSETSIZE)));

/* Initialize myset to only the lowest bit set */
myset = BITSET_T_INITIALIZER(0x1);
.Ed
.Sh SEE ALSO
.Xr bitstring 3 ,
.Xr cpuset 9
.Sh HISTORY
The
.Nm
macros first appeared in
.Fx 10.0
in January 2014.
They were MFCed to
.Fx 9.3 ,
released in July 2014.
.Pp
This manual page first appeared in
.Fx 11.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm
macros were generalized and pulled out of
.In sys/cpuset.h
as
.In sys/_bitset.h
and
.In sys/bitset.h
by
.An Attilio Rao Aq Mt attilio@FreeBSD.org .
This manual page was written by
.An Conrad Meyer Aq Mt cem@FreeBSD.org .
.Sh CAVEATS
The
.Fa SETSIZE
argument to all of these macros must match the value given to
.Fn BITSET_DEFINE .
.Pp
Unlike every other reference to individual set members, which are zero-indexed,
.Fn BIT_FFS ,
.Fn BIT_FFS_AT
and
.Fn BIT_FLS
return a one-indexed result (or zero if the set is empty).
.Pp
In order to use the macros defined in
.In sys/bitset.h
and
.In sys/_bitset.h
in userland programs,
.Dv _WANT_FREEBSD_BITSET
has to be defined before including the header files.
This requirements exists to prevent a name space pollution due to macros defined in
.Nm
in programs that include
.In sys/cpuset.h
or
.In sched.h .