FreeBSD/Linux Kernel Cross Reference
sys/kern/clock_subr.c

     /*      $OpenBSD: clock_subr.c,v 1.6 2016/08/26 07:09:56 guenther Exp $ */
     /*      $NetBSD: clock_subr.c,v 1.3 1997/03/15 18:11:16 is Exp $        */
     
     /*
      * Copyright (c) 1988 University of Utah.
      * Copyright (c) 1982, 1990, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
     * the Systems Programming Group of the University of Utah Computer
     * Science Department.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * from: Utah $Hdr: clock.c 1.18 91/01/21$
     *
     *      @(#)clock.c     8.2 (Berkeley) 1/12/94
     */
    
    /*
     * Generic routines to convert between a POSIX date
     * (seconds since 1/1/1970) and yr/mo/day/hr/min/sec
     * Derived from arch/hp300/hp300/clock.c
     */
    
    #include <sys/types.h>
    #include <sys/time.h>
    #include <sys/systm.h>
    
    static inline int leapyear(int year);
    #define FEBRUARY        2
    #define days_in_year(a)         (leapyear(a) ? 366 : 365)
    #define days_in_month(a)        (month_days[(a) - 1])
    
    static const int month_days[12] = {
            31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
    };
    
    /*
     * This inline avoids some unnecessary modulo operations
     * as compared with the usual macro:
     *   ( ((year % 4) == 0 &&
     *      (year % 100) != 0) ||
     *     ((year % 400) == 0) )
     * It is otherwise equivalent.
     */
    static inline int
    leapyear(int year)
    {
            int rv = 0;
    
            if ((year & 3) == 0) {
                    rv = 1;
                    if ((year % 100) == 0) {
                            rv = 0;
                            if ((year % 400) == 0)
                                    rv = 1;
                    }
            }
            return (rv);
    }
    
    time_t
    clock_ymdhms_to_secs(struct clock_ymdhms *dt)
    {
            time_t secs;
            int i, year, days;
    
            year = dt->dt_year;
    
            /*
             * Compute days since start of time.
             * First from years, then from months.
             */
            days = 0;
            for (i = POSIX_BASE_YEAR; i < year; i++)
                    days += days_in_year(i);
           if (leapyear(year) && dt->dt_mon > FEBRUARY)
                   days++;
   
           /* Months */
           for (i = 1; i < dt->dt_mon; i++)
                   days += days_in_month(i);
           days += (dt->dt_day - 1);
   
           /* Add hours, minutes, seconds. */
           secs = (time_t)((days
               * 24 + dt->dt_hour)
               * 60 + dt->dt_min)
               * 60 + dt->dt_sec;
   
           return (secs);
   }
   
   /* This function uses a copy of month_days[] */
   #undef  days_in_month
   #define days_in_month(a)        (mthdays[(a) - 1])
   
   void
   clock_secs_to_ymdhms(time_t secs, struct clock_ymdhms *dt)
   {
           int mthdays[12];
           int i, days;
           int rsec;       /* remainder seconds */
   
           memcpy(mthdays, month_days, sizeof(mthdays));
   
           days = secs / SECDAY;
           rsec = secs % SECDAY;
   
           /* Day of week (Note: 1/1/1970 was a Thursday) */
           dt->dt_wday = (days + 4) % 7;
   
           /* Subtract out whole years, counting them in i. */
           for (i = POSIX_BASE_YEAR; days >= days_in_year(i); i++)
                   days -= days_in_year(i);
           dt->dt_year = i;
   
           /* Subtract out whole months, counting them in i. */
           if (leapyear(i))
                   days_in_month(FEBRUARY) = 29;
           for (i = 1; days >= days_in_month(i); i++)
                   days -= days_in_month(i);
           dt->dt_mon = i;
   
           /* Days are what is left over (+1) from all that. */
           dt->dt_day = days + 1;
   
           /* Hours, minutes, seconds are easy */
           dt->dt_hour = rsec / 3600;
           rsec = rsec % 3600;
           dt->dt_min  = rsec / 60;
           rsec = rsec % 60;
           dt->dt_sec  = rsec;
   }

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