Date: Thu, 15 Nov 2018 16:02:14 +0000 (UTC) From: Warner Losh <imp@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r340450 - head/sys/sys Message-ID: <201811151602.wAFG2E4w040161@repo.freebsd.org>
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Author: imp Date: Thu Nov 15 16:02:13 2018 New Revision: 340450 URL: https://svnweb.freebsd.org/changeset/base/340450 Log: When converting ns,us,ms to sbt, return the ceil() of the result rather than the floor(). Returning the floor means that sbttoX(Xtosbt(y)) != y for almost all values of y. In practice, this results in a difference of at most 1 in the lsb of the sbintime_t. This difference is meaningless for all current users of these functions, but is important for the newly introduced sysctl conversion routines which implicitly rely on the transformation being idempotent. Sponsored by: Netflix, Inc Modified: head/sys/sys/time.h Modified: head/sys/sys/time.h ============================================================================== --- head/sys/sys/time.h Thu Nov 15 08:43:17 2018 (r340449) +++ head/sys/sys/time.h Thu Nov 15 16:02:13 2018 (r340450) @@ -161,6 +161,10 @@ sbttobt(sbintime_t _sbt) * Decimal<->sbt conversions. Multiplying or dividing by SBT_1NS results in * large roundoff errors which sbttons() and nstosbt() avoid. Millisecond and * microsecond functions are also provided for completeness. + * + * These functions return the smallest sbt larger or equal to the number of + * seconds requested so that sbttoX(Xtosbt(y)) == y. The 1 << 32 - 1 term added + * transforms the >> 32 from floor() to ceil(). */ static __inline int64_t sbttons(sbintime_t _sbt) @@ -173,7 +177,7 @@ static __inline sbintime_t nstosbt(int64_t _ns) { - return ((_ns * (((uint64_t)1 << 63) / 500000000)) >> 32); + return ((_ns * (((uint64_t)1 << 63) / 500000000) + (1ull << 32) - 1) >> 32); } static __inline int64_t @@ -187,7 +191,7 @@ static __inline sbintime_t ustosbt(int64_t _us) { - return ((_us * (((uint64_t)1 << 63) / 500000)) >> 32); + return ((_us * (((uint64_t)1 << 63) / 500000) + (1ull << 32) - 1) >> 32); } static __inline int64_t @@ -201,7 +205,7 @@ static __inline sbintime_t mstosbt(int64_t _ms) { - return ((_ms * (((uint64_t)1 << 63) / 500)) >> 32); + return ((_ms * (((uint64_t)1 << 63) / 500) + (1ull << 32) - 1) >> 32); } /*-
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