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freebsd-dev/share/man/man3/bitstring.3
Doug Moore 84e2ae64c5 vm_reserv: use enhanced bitstring for popmaps 
vm_reserv.c uses its own bitstring implemenation for popmaps. Using
the bitstring_t type from a standard header eliminates the code
duplication, allows some bit-at-a-time operations to be replaced with
more efficient bitstring range operations, and, in
vm_reserv_test_contig, allows bit_ffc_area_at to more efficiently
search for a big-enough set of consecutive zero-bits.

Make bitstring changes improve the vm_reserv code.  Define a bit_ntest
method to test whether a range of bits is all set, or all clear.
Define bit_ff_at and bit_ff_area_at to implement the ffs and ffc
versions with a parameter to choose between set- and clear- bits.
Improve the area_at implementation.  Modify the bit_nset and
bit_nclear implementations to allow code optimization in the cases
when start or end are multiples of _BITSTR_BITS.

Add a few new cases to bitstring_test.

Discussed with:	alc
Reviewed by:	markj
Tested by:	pho (earlier version)
Differential Revision:	https://reviews.freebsd.org/D33312
2022-01-12 11:03:53 -06:00

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.\" @(#)bitstring.3 8.1 (Berkeley) 7/19/93
.\" $FreeBSD$
.\"
.Dd August 8, 2021
.Dt BITSTRING 3
.Os
.Sh NAME
.Nm bit_alloc ,
.Nm bit_clear ,
.Nm bit_count ,
.Nm bit_decl ,
.Nm bit_ffc ,
.Nm bit_ffs ,
.Nm bit_ff_at ,
.Nm bit_ffc_at ,
.Nm bit_ffs_at ,
.Nm bit_ffc_area ,
.Nm bit_ffs_area ,
.Nm bit_ff_area_at ,
.Nm bit_ffc_area_at ,
.Nm bit_ffs_area_at ,
.Nm bit_nclear ,
.Nm bit_nset ,
.Nm bit_ntest ,
.Nm bit_set ,
.Nm bit_test ,
.Nm bitstr_size
.Nd bit-string manipulation functions and macros
.Sh SYNOPSIS
.In bitstring.h
.Ft bitstr_t *
.Fn bit_alloc "int nbits"
.Ft void
.Fn bit_decl "bitstr_t *name" "int nbits"
.Ft void
.Fn bit_clear "bitstr_t *name" "int bit"
.Ft void
.Fn bit_count "bitstr_t *name" "int count" "int nbits" "int *value"
.Ft void
.Fn bit_ffc "bitstr_t *name" "int nbits" "int *value"
.Ft void
.Fn bit_ffs "bitstr_t *name" "int nbits" "int *value"
.Ft void
.Fn bit_ffc_at "bitstr_t *name" "int start" "int nbits" "int *value"
.Ft void
.Fn bit_ffs_at "bitstr_t *name" "int start" "int nbits" "int *value"
.Ft void
.Fn bit_ff_at "bitstr_t *name" "int start" "int nbits" "int match" "int *value"
.Ft void
.Fn bit_ffc_area "bitstr_t *name" "int nbits" "int size" "int *value"
.Ft void
.Fn bit_ffs_area "bitstr_t *name" "int nbits" "int size" "int *value"
.Ft void
.Fn bit_ffc_area_at "bitstr_t *name" "int start" "int nbits" "int size" "int *value"
.Ft void
.Fn bit_ffs_area_at "bitstr_t *name" "int start" "int nbits" "int size" "int *value"
.Ft void
.Fn bit_ff_area_at "bitstr_t *name" "int start" "int nbits" "int size" "int match" "int *value"
.Fn bit_foreach "bitstr_t *name" "int nbits" "int var"
.Fn bit_foreach_at "bitstr_t *name" "int start" "int nbits" "int var"
.Fn bit_foreach_unset "bitstr_t *name" "int nbits" "int var"
.Fn bit_foreach_unset_at "bitstr_t *name" "int start" "int nbits" "int var"
.Ft void
.Fn bit_nclear "bitstr_t *name" "int start" "int stop"
.Ft void
.Fn bit_nset "bitstr_t *name" "int start" "int stop"
.Ft int
.Fn bit_ntest "bitstr_t *name" "int start" "int stop" "int match"
.Ft void
.Fn bit_set "bitstr_t *name" "int bit"
.Ft int
.Fn bitstr_size "int nbits"
.Ft int
.Fn bit_test "bitstr_t *name" "int bit"
.Sh DESCRIPTION
These macros operate on strings of bits.
.Pp
The function
.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.
If successful, the returned bit string is initialized with all bits cleared.
.Pp
The macro
.Fn bit_decl
declares a bit string with sufficient space to store
.Fa nbits
bits.
.Fn bit_decl
may be used to include statically sized bit strings in structure
definitions or to create bit strings on the stack.
Users of this macro are responsible for initialization of the bit string,
typically via a global initialization of the containing struct or use of the
.Fn bit_nset
or
.Fn bin_nclear
functions.
.Pp
The macro
.Fn bitstr_size
returns the number of bytes necessary to store
.Fa nbits
bits.
This is useful for copying bit strings.
.Pp
The functions
.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
functions
set or clear the zero-based numbered bits from
.Fa start
through
.Fa stop
in the bit string
.Ar name .
.Pp
The
.Fn bit_test
function
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_ntest
function
evaluates to non-zero if the zero-based numbered bits from
.Fa start
through
.Fa stop
in the bit string
.Ar name
all have the value
.Ar match .
.Pp
The function
.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
.Fn bit_ffs
function
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 function
.Fn bit_ffc_at
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 ,
at or after the zero-based bit index
.Fa start .
If all bits at or after
.Fa start
are set, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffs_at
function
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 ,
at or after the zero-based bit index
.Fa start .
If no bits are set after
.Fa start ,
the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ff_at
function
stores in the location referenced by
.Fa value
the zero-based number of the first bit in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start
that has value
.Fa match .
If no bits after
.Fa start
match that value, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffc_area
function stores in the location referenced by
.Fa value
the zero-based number of the first bit beginning a sequence of unset bits of
at least
.Fa size
unset bits in the array of
.Fa nbits
bits referenced by
.Fa name .
If no sequence of contiguous unset bits of the specified
.Fa size
can be found, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffs_area
function stores in the location referenced by
.Fa value
the zero-based number of the first bit beginning a sequence of set bits of
at least
.Fa size
set bits in the array of
.Fa nbits
bits referenced by
.Fa name .
If no sequence of contiguous set bits of the specified
.Fa size
can be found, the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffc_area_at
function stores in the location referenced by
.Fa value
the zero-based number of the first bit beginning a sequence of unset bits of
at least
.Fa size
unset bits in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
If no sequence of contiguous unset bits of the specified
.Fa size
can be found at or after
.Fa start ,
the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ffs_area_at
function stores in the location referenced by
.Fa value
the zero-based number of the first bit beginning a sequence of set bits of
at least
.Fa size
set bits in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
If no sequence of contiguous set bits of the specified
.Fa size
can be found at or after
.Fa start ,
the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_ff_area_at
function stores in the location referenced by
.Fa value
the zero-based number of the first bit beginning a sequence of bits of
at least
.Fa size
bits in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start
in which all bits have the value
.Fa match .
If no sequence of contiguous such bits of the specified
.Fa size
can be found at or after
.Fa start ,
the location referenced by
.Fa value
is set to \-1.
.Pp
The
.Fn bit_count
function stores in the location referenced by
.Fa value
the number of bits set in the array of
.Fa nbits
bits referenced by
.Fa name ,
at or after the zero-based bit index
.Fa start .
.Pp
The macro
.Fn bit_foreach
traverses all set bits in the array of
.Fa nbits
referenced by
.Fa name
in the forward direction, assigning each location in turn to
.Fa var .
.Pp
The macro
.Fn bit_foreach_at
traverses all set bits in the array of
.Fa nbits
referenced by
.Fa name
in the forward direction at or after the zero-based bit index
.Fa start ,
assigning each location in turn to
.Fa var .
.Pp
The macro
.Fn bit_foreach_unset
traverses all unset bits in the array of
.Fa nbits
referenced by
.Fa name
in the forward direction, assigning each location in turn to
.Fa var .
.Pp
The macro
.Fn bit_foreach_unset_at
traverses all unset bits in the array of
.Fa nbits
referenced by
.Fa name
in the forward direction at or after the zero-based bit index
.Fa start ,
assigning each location in turn to
.Fa var .
.Pp
The arguments in bit string 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 ,
.Xr bitset 9
.Sh HISTORY
The
.Nm bitstring
functions first appeared in
.Bx 4.4 .
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