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Add bit_count to the bitstring(3) api

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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
This commit is contained in:
Alan Somers 2016-05-23 20:29:18 +00:00
parent fc13dfc8e2
commit 1b82e02f4d
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=300539
6 changed files with 127 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
UPDATING
View File

@ -31,6 +31,12 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 11.x IS SLOW:
disable the most expensive debugging functionality run
"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
20160523:
The bitstring(3) API has been updated with new functionality and
improved performance. But it is binary-incompatible with the old API.
Objects built with the new headers may not be linked against objects
built with the old headers.
20160520:
The brk and sbrk functions have been removed from libc on arm64.
Binutils from ports has been updated to not link to these

18
share/man/man3/bitstring.3
View File

@ -27,7 +27,7 @@
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" Copyright (c) 2014 Spectra Logic Corporation
.\" Copyright (c) 2014,2016 Spectra Logic Corporation
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
@ -58,12 +58,13 @@
.\" @(#)bitstring.3 8.1 (Berkeley) 7/19/93
.\" $FreeBSD$
.\"
.Dd May 4, 2016
.Dd May 23, 2016
.Dt BITSTRING 3
.Os
.Sh NAME
.Nm bit_alloc ,
.Nm bit_clear ,
.Nm bit_count ,
.Nm bit_decl ,
.Nm bit_ffc ,
.Nm bit_ffs ,
@ -84,6 +85,8 @@
.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"
@ -225,6 +228,17 @@ 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 arguments in bit string macros are evaluated only once and may safely
have side effects.
.Sh EXAMPLES

7
sys/kern/subr_unit.c
View File

@ -224,7 +224,8 @@ check_unrhdr(struct unrhdr *uh, int line)
{
struct unr *up;
struct unrb *ub;
u_int x, y, z, w;
int w;
u_int y, z;
y = uh->first;
z = 0;
@ -237,9 +238,7 @@ check_unrhdr(struct unrhdr *uh, int line)
up->len, NBITS, line));
z++;
w = 0;
for (x = 0; x < up->len; x++)
if (bit_test(ub->map, x))
w++;
bit_count(ub->map, 0, up->len, &w);
y += w;
} else if (up->ptr != NULL)
y += up->len;

41
sys/sys/bitstring.h
View File

@ -65,6 +65,7 @@
#ifdef _KERNEL
#include <sys/libkern.h>
#include <sys/malloc.h>
#include <sys/types.h>
#endif
typedef unsigned long bitstr_t;
@ -202,7 +203,7 @@ bit_ffs_at(bitstr_t *_bitstr, int _start, int _nbits, int *_result)
_test &= _bit_make_mask(_start, _BITSTR_BITS - 1);
while (_test == 0 && _curbitstr < _stopbitstr)
_test = *(++_curbitstr);
_offset = ffsl(_test);
_value = ((_curbitstr - _bitstr) * _BITSTR_BITS) + _offset - 1;
if (_offset == 0 || _value >= _nbits)
@ -231,7 +232,7 @@ bit_ffc_at(bitstr_t *_bitstr, int _start, int _nbits, int *_result)
_test |= _bit_make_mask(0, _start - 1);
while (_test == _BITSTR_MASK && _curbitstr < _stopbitstr)
_test = *(++_curbitstr);
_offset = ffsl(~_test);
_value = ((_curbitstr - _bitstr) * _BITSTR_BITS) + _offset - 1;
if (_offset == 0 || _value >= _nbits)
@ -256,4 +257,40 @@ bit_ffc(bitstr_t *_bitstr, int _nbits, int *_result)
bit_ffc_at(_bitstr, /*start*/0, _nbits, _result);
}
/* Count the number of bits set in a bitstr of size _nbits at or after _start */
static inline void
bit_count(bitstr_t *_bitstr, int _start, int _nbits, int *_result)
{
bitstr_t *_curbitstr, mask;
int _value = 0, curbitstr_len;
if (_start >= _nbits)
goto out;
_curbitstr = _bitstr + _bit_idx(_start);
_nbits -= _BITSTR_BITS * _bit_idx(_start);
_start -= _BITSTR_BITS * _bit_idx(_start);
if (_start > 0) {
curbitstr_len = (int)_BITSTR_BITS < _nbits ?
(int)_BITSTR_BITS : _nbits;
mask = _bit_make_mask(_start, _bit_offset(curbitstr_len - 1));
_value += __bitcountl(*_curbitstr & mask);
_curbitstr++;
_nbits -= _BITSTR_BITS;
}
while (_nbits >= (int)_BITSTR_BITS) {
_value += __bitcountl(*_curbitstr);
_curbitstr++;
_nbits -= _BITSTR_BITS;
}
if (_nbits > 0) {
mask = _bit_make_mask(0, _bit_offset(_nbits - 1));
_value += __bitcountl(*_curbitstr & mask);
}
out:
*_result = _value;
}
#endif /* _SYS_BITSTRING_H_ */

2
sys/sys/param.h
View File

@ -58,7 +58,7 @@
* in the range 5 to 9.
*/
#undef __FreeBSD_version
#define __FreeBSD_version 1100111 /* Master, propagated to newvers */
#define __FreeBSD_version 1100112 /* Master, propagated to newvers */
/*
* __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,

62
tests/sys/sys/bitstring_test.c
View File

@ -342,6 +342,67 @@ BITSTRING_TC_DEFINE(bit_nset)
}
}
BITSTRING_TC_DEFINE(bit_count)
/* bitstr_t *bitstr, int nbits, const char *memloc */
{
int result, s, e, expected;
/* Empty bitstr */
memset(bitstr, 0, bitstr_size(nbits));
bit_count(bitstr, 0, nbits, &result);
ATF_CHECK_MSG(0 == result,
"bit_count_%d_%s_%s: Failed with result %d",
nbits, "clear", memloc, result);
/* Full bitstr */
memset(bitstr, 0xFF, bitstr_size(nbits));
bit_count(bitstr, 0, nbits, &result);
ATF_CHECK_MSG(nbits == result,
"bit_count_%d_%s_%s: Failed with result %d",
nbits, "set", memloc, result);
/* Invalid _start value */
memset(bitstr, 0xFF, bitstr_size(nbits));
bit_count(bitstr, nbits, nbits, &result);
ATF_CHECK_MSG(0 == result,
"bit_count_%d_%s_%s: Failed with result %d",
nbits, "invalid_start", memloc, result);
/* Alternating bitstr, starts with 0 */
memset(bitstr, 0xAA, bitstr_size(nbits));
bit_count(bitstr, 0, nbits, &result);
ATF_CHECK_MSG(nbits / 2 == result,
"bit_count_%d_%s_%d_%s: Failed with result %d",
nbits, "alternating", 0, memloc, result);
/* Alternating bitstr, starts with 1 */
memset(bitstr, 0x55, bitstr_size(nbits));
bit_count(bitstr, 0, nbits, &result);
ATF_CHECK_MSG((nbits + 1) / 2 == result,
"bit_count_%d_%s_%d_%s: Failed with result %d",
nbits, "alternating", 1, memloc, result);
/* Varying start location */
memset(bitstr, 0xAA, bitstr_size(nbits));
for (s = 0; s < nbits; s++) {
expected = s % 2 == 0 ? (nbits - s) / 2 : (nbits - s + 1) / 2;
bit_count(bitstr, s, nbits, &result);
ATF_CHECK_MSG(expected == result,
"bit_count_%d_%s_%d_%s: Failed with result %d",
nbits, "vary_start", s, memloc, result);
}
/* Varying end location */
memset(bitstr, 0xAA, bitstr_size(nbits));
for (e = 0; e < nbits; e++) {
bit_count(bitstr, 0, e, &result);
ATF_CHECK_MSG(e / 2 == result,
"bit_count_%d_%s_%d_%s: Failed with result %d",
nbits, "vary_end", e, memloc, result);
}
}
ATF_TP_ADD_TCS(tp)
{
@ -354,6 +415,7 @@ ATF_TP_ADD_TCS(tp)
BITSTRING_TC_ADD(tp, bit_ffc_at);
BITSTRING_TC_ADD(tp, bit_nclear);
BITSTRING_TC_ADD(tp, bit_nset);
BITSTRING_TC_ADD(tp, bit_count);
return (atf_no_error());
}