Date: Fri, 14 Jul 2017 18:36:15 +0000 (UTC) From: Ian Lepore <ian@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r320997 - head/sys/kern Message-ID: <201707141836.v6EIaF8R015055@repo.freebsd.org>
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Author: ian Date: Fri Jul 14 18:36:15 2017 New Revision: 320997 URL: https://svnweb.freebsd.org/changeset/base/320997 Log: Minor optimization: instead of converting between days and years using loops that start in 1970, assume most conversions are going to be for recent dates and use a precomputed number of days through the end of 2016. Modified: head/sys/kern/subr_clock.c Modified: head/sys/kern/subr_clock.c ============================================================================== --- head/sys/kern/subr_clock.c Fri Jul 14 18:13:54 2017 (r320996) +++ head/sys/kern/subr_clock.c Fri Jul 14 18:36:15 2017 (r320997) @@ -97,6 +97,13 @@ static const int month_days[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }; +/* + * Optimization: using a precomputed count of days between POSIX_BASE_YEAR and a + * recent year avoids lots of needless loop iterations in conversion. + * recent_base_days is the number of days through the end of recent_base_year. + */ +static const int recent_base_year = 2016; +static const int recent_base_days = 17167; /* * This inline avoids some unnecessary modulo operations @@ -157,8 +164,14 @@ clock_ct_to_ts(struct clocktime *ct, struct timespec * * Compute days since start of time * First from years, then from months. */ - days = 0; - for (i = POSIX_BASE_YEAR; i < year; i++) + if (year > recent_base_year) { + i = recent_base_year; + days = recent_base_days; + } else { + i = POSIX_BASE_YEAR; + days = 0; + } + for (; i < year; i++) days += days_in_year(i); /* Months */ @@ -188,8 +201,14 @@ clock_ts_to_ct(struct timespec *ts, struct clocktime * ct->dow = day_of_week(days); - /* Subtract out whole years, counting them in i. */ - for (year = POSIX_BASE_YEAR; days >= days_in_year(year); year++) + /* Subtract out whole years. */ + if (days >= recent_base_days) { + year = recent_base_year + 1; + days -= recent_base_days; + } else { + year = POSIX_BASE_YEAR; + } + for (; days >= days_in_year(year); year++) days -= days_in_year(year); ct->year = year;
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