lib/ansi/mktime.c

   1 /*
   2  * mktime - convert local time into calendar time
   3  */
   4 /* $Header$ */
   5
   6 /* Michael A. Temari <temari@ix.netcom.com>   03/01/96    */
   7 /*   -  fixed bug is structure fixup code                 */
   8
   9 #include        <time.h>
  10 #include        <limits.h>
  11 #include        "loc_time.h"
  12
  13 /* The code assumes that unsigned long can be converted to time_t.
  14  * A time_t should not be wider than unsigned long, since this would mean
  15  * that the check for overflow at the end could fail.
  16  */
  17 time_t
  18 mktime(register struct tm *timep)
  19 {
  20         register long day, year;
  21         register int tm_year;
  22         int yday, month;
  23         register unsigned long seconds;
  24         int overflow;
  25         unsigned dst;
  26
  27         timep->tm_min += timep->tm_sec / 60;
  28         timep->tm_sec %= 60;
  29         if (timep->tm_sec < 0) {
  30                 timep->tm_sec += 60;
  31                 timep->tm_min--;
  32         }
  33         timep->tm_hour += timep->tm_min / 60;
  34         timep->tm_min = timep->tm_min % 60;
  35         if (timep->tm_min < 0) {
  36                 timep->tm_min += 60;
  37                 timep->tm_hour--;
  38         }
  39         day = timep->tm_hour / 24;
  40         timep->tm_hour= timep->tm_hour % 24;
  41         if (timep->tm_hour < 0) {
  42                 timep->tm_hour += 24;
  43                 day--;
  44         }
  45         timep->tm_year += timep->tm_mon / 12;
  46         timep->tm_mon %= 12;
  47         if (timep->tm_mon < 0) {
  48                 timep->tm_mon += 12;
  49                 timep->tm_year--;
  50         }
  51         day += (timep->tm_mday - 1);
  52         while (day < 0) {
  53                 if(--timep->tm_mon < 0) {
  54                         timep->tm_year--;
  55                         timep->tm_mon = 11;
  56                 }
  57                 day += _ytab[LEAPYEAR(YEAR0 + timep->tm_year)][timep->tm_mon];
  58         }
  59         while (day >= _ytab[LEAPYEAR(YEAR0 + timep->tm_year)][timep->tm_mon]) {
  60                 day -= _ytab[LEAPYEAR(YEAR0 + timep->tm_year)][timep->tm_mon];
  61                 if (++(timep->tm_mon) == 12) {
  62                         timep->tm_mon = 0;
  63                         timep->tm_year++;
  64                 }
  65         }
  66         timep->tm_mday = day + 1;
  67         _tzset();                       /* set timezone and dst info  */
  68         year = EPOCH_YR;
  69         if (timep->tm_year < year - YEAR0) return (time_t)-1;
  70         seconds = 0;
  71         day = 0;                        /* means days since day 0 now */
  72         overflow = 0;
  73
  74         /* Assume that when day becomes negative, there will certainly
  75          * be overflow on seconds.
  76          * The check for overflow needs not to be done for leapyears
  77          * divisible by 400.
  78          * The code only works when year (1970) is not a leapyear.
  79          */
  80 #if     EPOCH_YR != 1970
  81 #error  EPOCH_YR != 1970
  82 #endif
  83         tm_year = timep->tm_year + YEAR0;
  84
  85         if (LONG_MAX / 365 < tm_year - year) overflow++;
  86         day = (tm_year - year) * 365;
  87         if (LONG_MAX - day < (tm_year - year) / 4 + 1) overflow++;
  88         day += (tm_year - year) / 4
  89                 + ((tm_year % 4) && tm_year % 4 < year % 4);
  90         day -= (tm_year - year) / 100
  91                 + ((tm_year % 100) && tm_year % 100 < year % 100);
  92         day += (tm_year - year) / 400
  93                 + ((tm_year % 400) && tm_year % 400 < year % 400);
  94
  95         yday = month = 0;
  96         while (month < timep->tm_mon) {
  97                 yday += _ytab[LEAPYEAR(tm_year)][month];
  98                 month++;
  99         }
 100         yday += (timep->tm_mday - 1);
 101         if (day + yday < 0) overflow++;
 102         day += yday;
 103
 104         timep->tm_yday = yday;
 105         timep->tm_wday = (day + 4) % 7;         /* day 0 was thursday (4) */
 106
 107         seconds = ((timep->tm_hour * 60L) + timep->tm_min) * 60L + timep->tm_sec;
 108
 109         if ((TIME_MAX - seconds) / SECS_DAY < day) overflow++;
 110         seconds += day * SECS_DAY;
 111
 112         /* Now adjust according to timezone and daylight saving time */
 113
 114         if (((_timezone > 0) && (TIME_MAX - _timezone < seconds))
 115             || ((_timezone < 0) && (seconds < -_timezone)))
 116                 overflow++;
 117         seconds += _timezone;
 118
 119         if (timep->tm_isdst < 0)
 120                 dst = _dstget(timep);
 121         else if (timep->tm_isdst)
 122                 dst = _dst_off;
 123         else dst = 0;
 124
 125         if (dst > seconds) overflow++;  /* dst is always non-negative */
 126         seconds -= dst;
 127
 128         if (overflow) return (time_t)-1;
 129
 130         if ((time_t)seconds != seconds) return (time_t)-1;
 131         return (time_t)seconds;
 132 }