Date: Thu, 6 Jul 2017 21:47:18 +0000 (UTC) From: Konstantin Belousov <kib@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r320755 - in head: share/man/man9 sys/sys Message-ID: <201707062147.v66LlIPu023692@repo.freebsd.org>
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Author: kib Date: Thu Jul 6 21:47:17 2017 New Revision: 320755 URL: https://svnweb.freebsd.org/changeset/base/320755 Log: 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. Submitted by: Sebastian Huber <sebastian.huber@embedded-brains.de> MFC after: 1 week Modified: head/share/man/man9/bitset.9 head/sys/sys/bitset.h Modified: head/share/man/man9/bitset.9 ============================================================================== --- head/share/man/man9/bitset.9 Thu Jul 6 19:53:30 2017 (r320754) +++ head/share/man/man9/bitset.9 Thu Jul 6 21:47:17 2017 (r320755) @@ -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 @@ -275,6 +278,23 @@ 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_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 Modified: head/sys/sys/bitset.h ============================================================================== --- head/sys/sys/bitset.h Thu Jul 6 19:53:30 2017 (r320754) +++ head/sys/sys/bitset.h Thu Jul 6 21:47:17 2017 (r320755) @@ -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; \
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