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bitset: add BIT_FFS_AT() for finding the first bit set greater than a start bit

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Reviewed by:	kib
Approved by:	scottl (implicit)
MFC after:	1 week
Sponsored by:	Ampere Computing, Inc.
Differential Revision:	https://reviews.freebsd.org/D26128
This commit is contained in:
scottph 2020-08-26 02:07:46 +00:00
parent fd01b57e63
commit 4401c86345
2 changed files with 33 additions and 6 deletions
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20
share/man/man9/bitset.9
View File

@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd December 12, 2019
.Dd August 25, 2020
.Dt BITSET 9
.Os
.Sh NAME
@ -43,6 +43,7 @@
.Nm BIT_EMPTY ,
.Nm BIT_ISFULLSET ,
.Nm BIT_FFS ,
.Nm BIT_FFS_AT ,
.Nm BIT_FLS ,
.Nm BIT_COUNT ,
.Nm BIT_SUBSET ,
@ -86,6 +87,8 @@
.Ft int
.Fn BIT_FFS "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft int
.Fn BIT_FFS_AT "const SETSIZE" "struct STRUCTNAME *bitset" "int start"
.Ft int
.Fn BIT_FLS "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft int
.Fn BIT_COUNT "const SETSIZE" "struct STRUCTNAME *bitset"
@ -285,6 +288,18 @@ index parameter to any other
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 ,
@ -518,7 +533,8 @@ 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 ,
.Fn BIT_FFS_AT
and
.Fn BIT_FLS
return a one-indexed result (or zero if the set is empty).

19
sys/sys/bitset.h
View File

@ -207,21 +207,32 @@
(f)->__bits[__i]); \
} while (0)
#define BIT_FFS(_s, p) __extension__ ({ \
/*
* Note that `start` and the returned value from BIT_FFS_AT are
* 1-based bit indices.
*/
#define BIT_FFS_AT(_s, p, start) __extension__ ({ \
__size_t __i; \
long __mask; \
int __bit; \
\
__mask = ~0UL << ((start) % _BITSET_BITS); \
__bit = 0; \
for (__i = 0; __i < __bitset_words((_s)); __i++) { \
if ((p)->__bits[__i] != 0) { \
__bit = ffsl((p)->__bits[__i]); \
for (__i = __bitset_word((_s), (start)); \
__i < __bitset_words((_s)); \
__i++) { \
if (((p)->__bits[__i] & __mask) != 0) { \
__bit = ffsl((p)->__bits[__i] & __mask); \
__bit += __i * _BITSET_BITS; \
break; \
} \
__mask = ~0UL; \
} \
__bit; \
})
#define BIT_FFS(_s, p) BIT_FFS_AT((_s), (p), 0)
#define BIT_FLS(_s, p) __extension__ ({ \
__size_t __i; \
int __bit; \