/*      $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;
}