Subversion Repositories planix.SVN

#include <time.h>

/*
 * BUG: Doesn't do leap years in full glory,
 * or calendar changes. In 2038 the sign bit
 * will be needed in time_t, but we say it
 * can't be represented.
 */
static int
dysize(int y)
{
        y += 1900; /* arg is a tm_year, number of years since 1900 */
        if((y%4) == 0 && ((y%100) !=0 || (y%400) == 0))
                return 366;
        return 365;
}

static int
dmsize(int m, int y)
{
        static  char    sizes[12] =
                { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

        if(m == 1)
                return (dysize(y)==366)? 29 : 28;
        else
                return sizes[m];
}

/* Reduce *v to [0, mult), adding 1 to *next for every mult
 * subtracted from *v, and return 1 if reduction worked (no overflow)
 */
static int
reduce(int *v, int *next, int mult)
{
        int oldnext;

        while(*v < 0){
                *v += mult;
                oldnext = *next;
                --*next;
                if(!(*next < oldnext))
                        return 0;
        }
        while(*v >= mult){
                *v -= mult;
                oldnext = *next;
                ++*next;
                if(!(*next > oldnext))
                        return 0;
        }
        return 1;
}

static int
jan1(int yr)
{
        int y, d;

        y = yr+1900;
        d = (4+y+(y+3)/4-(y-1701)/100+(y-1601)/400+3)%7;
        return d;
}

time_t
mktime(struct tm *t)
{
        time_t a;
        int i, d;
        struct tm *ptm;

        if(!(reduce(&t->tm_sec, &t->tm_min, 60) &&
             reduce(&t->tm_min, &t->tm_hour, 60) &&
             reduce(&t->tm_hour, &t->tm_mday, 24) &&
             reduce(&t->tm_mon, &t->tm_year, 12)))
                return -1;
        while(t->tm_mday < 1){
                if(--t->tm_mon == -1){
                        t->tm_mon = 11;
                        t->tm_year--;
                }
                t->tm_mday += dmsize(t->tm_mon, t->tm_year);
        }
        while(t->tm_mday > dmsize(t->tm_mon, t->tm_year)){
                t->tm_mday -= dmsize(t->tm_mon, t->tm_year);
                if(++t->tm_mon == 12){
                        t->tm_mon = 0;
                        t->tm_year++;
                }
        }
        a = t->tm_sec + 60*t->tm_min + 3600*t->tm_hour;
        t->tm_yday = t->tm_mday-1;
        for(i=0; i<t->tm_mon; i++)
                t->tm_yday += dmsize(i, t->tm_year);
        a += t->tm_yday*86400L;
        if(t->tm_year < 70){
                for(i=t->tm_year; i<70; i++)
                        if((a -= dysize(i)*86400L) < 0)
                                return -1;
        }else if(t->tm_year > 70){
                for(i=70; i<t->tm_year; i++)
                        if((a += dysize(i)*86400L) < 0)
                                return -1;
        }
        /*
         * Now a is number of seconds past Jan 1 1970.
         * Convert to GMT.
         */
        ptm = gmtime(&a);
        d = ptm->tm_hour;
        ptm = localtime(&a);
        d -= ptm->tm_hour;
        if(d < 0)
                d += 24;
        if(t->tm_isdst == 0 && ptm->tm_isdst)
                d--;
        if(t->tm_isdst > 0 && !ptm->tm_isdst)
                d++;
        a += d*3600;
        t->tm_wday = (jan1(t->tm_year)+t->tm_yday)%7;
        return a;
}