Date: Thu, 6 Jul 2017 15:24:40 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: freebsd-hackers@freebsd.org Cc: kib@freebsd.org Subject: [PATCH] bitset(9): Add BIT_FLS() Message-ID: <20170706132440.18520-1-sebastian.huber@embedded-brains.de>
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Add BIT_FLS() analogous to BIT_FFS(). The benefit of BIT_FLS() is that
ffsl() can be implemented with a count leading zeros instruction which
is more widespread available.
---
share/man/man9/bitset.9 | 22 +++++++++++++++++++++-
sys/sys/bitset.h | 15 +++++++++++++++
2 files changed, 36 insertions(+), 1 deletion(-)
diff --git a/share/man/man9/bitset.9 b/share/man/man9/bitset.9
index d4060ace24c..f7f8a502b04 100644
--- a/share/man/man9/bitset.9
+++ b/share/man/man9/bitset.9
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd May 24, 2017
+.Dd July 6, 2017
.Dt BITSET 9
.Os
.Sh NAME
@@ -43,6 +43,7 @@
.Nm BIT_EMPTY ,
.Nm BIT_ISFULLSET ,
.Nm BIT_FFS ,
+.Nm BIT_FLS ,
.Nm BIT_COUNT ,
.Nm BIT_SUBSET ,
.Nm BIT_OVERLAP ,
@@ -85,6 +86,8 @@
.Ft int
.Fn BIT_FFS "const SETSIZE" "struct STRUCTNAME *bitset"
.Ft int
+.Fn BIT_FLS "const SETSIZE" "struct STRUCTNAME *bitset"
+.Ft int
.Fn BIT_COUNT "const SETSIZE" "struct STRUCTNAME *bitset"
.\"
.Ft bool
@@ -282,6 +285,23 @@ index parameter to any other
macro, you must subtract one from the result.
.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_COUNT
macro returns the total number of set bits in
.Fa bitset .
diff --git a/sys/sys/bitset.h b/sys/sys/bitset.h
index 8bc9e3d87a0..1ed19531b3b 100644
--- a/sys/sys/bitset.h
+++ b/sys/sys/bitset.h
@@ -213,6 +213,21 @@
__bit; \
})
+#define BIT_FLS(_s, p) __extension__ ({ \
+ __size_t __i; \
+ int __bit; \
+ \
+ __bit = 0; \
+ for (__i = __bitset_words((_s)) - 1; __i >= 0; __i--) { \
+ if ((p)->__bits[__i] != 0) { \
+ __bit = flsl((p)->__bits[__i]); \
+ __bit += __i * _BITSET_BITS; \
+ break; \
+ } \
+ } \
+ __bit; \
+})
+
#define BIT_COUNT(_s, p) __extension__ ({ \
__size_t __i; \
int __count; \
--
2.12.3
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