diff options
Diffstat (limited to 'mktime.c')
| -rw-r--r-- | mktime.c | 257 |
1 files changed, 257 insertions, 0 deletions
diff --git a/mktime.c b/mktime.c new file mode 100644 index 0000000..0f1edc5 --- /dev/null +++ b/mktime.c @@ -0,0 +1,257 @@ +/* free mktime function + Copyright 1988, 1989 by David MacKenzie <djm@ai.mit.edu> + and Michael Haertel <mike@ai.mit.edu> + Unlimited distribution permitted provided this copyright notice is + retained and any functional modifications are prominently identified. */ + +/* Revised 1997 by Christian Spieler: + The code was changed to get more conformance with ANSI's (resp. modern + UNIX releases) definition for mktime(): + - Added adjustment for out-of-range values in the fields of struct tm. + - Added iterations to get the correct UTC result for input values at + the gaps when daylight saving time is switched on or off. + - Allow forcing of DST "on" or DST "off" by setting `tm_isdst' field in + the tm struct to positive number resp. zero. The `tm_isdst' field must + be negative on entrance of mktime() to enable automatic determination + if DST is in effect for the requested local time. + - Added optional check for overflowing the time_t range. */ + +/* Note: This version of mktime is ignorant of the tzfile. + When the tm structure passed to mktime represents a local time that + is valid both as DST time and as standard time (= time value in the + gap when switching from DST back to standard time), the behaviour + for `tm_isdst < 0' depends on the current timezone: TZ east of GMT + assumes winter time, TZ west of GMT assumes summer time. + Although mktime() (resp. mkgmtime()) tries to adjust for invalid values + of struct tm members, this may fail for input values that are far away + from the valid ranges. The adjustment process does not check for overflows + or wrap arounds in the struct tm components. */ + +#ifndef OF +# ifdef __STDC__ +# define OF(a) a +# else +# define OF(a) () +# endif +#endif + +#ifndef ZCONST +# define ZCONST const +#endif + +#include <time.h> + +time_t mkgmtime OF((struct tm *)); +time_t mktime OF((struct tm *)); + +/* Return the equivalent in seconds past 12:00:00 a.m. Jan 1, 1970 GMT + of the local time and date in the exploded time structure `tm', + adjust out of range fields in `tm' and set `tm->tm_yday', `tm->tm_wday'. + If `tm->tm_isdst < 0' was passed to mktime(), the correct setting of + tm_isdst is determined and returned. Otherwise, mktime() assumes this + field as valid; its information is used when converting local time + to UTC. + Return -1 if time in `tm' cannot be represented as time_t value. */ + +time_t +mktime(tm) + struct tm *tm; +{ + struct tm *ltm; /* Local time. */ + time_t loctime; /* The time_t value of local time. */ + time_t then; /* The time to return. */ + long tzoffset_adj; /* timezone-adjustment `remainder' */ + int bailout_cnt; /* counter of tries for tz correction */ + int save_isdst; /* Copy of the tm->isdst input value */ + + save_isdst = tm->tm_isdst; + loctime = mkgmtime(tm); + if (loctime == -1) { + tm->tm_isdst = save_isdst; + return (time_t)-1; + } + + /* Correct for the timezone and any daylight savings time. + The correction is verified and repeated when not correct, to + take into account the rare case that a change to or from daylight + savings time occurs between when it is the time in `tm' locally + and when it is that time in Greenwich. After the second correction, + the "timezone & daylight" offset should be correct in all cases. To + be sure, we allow a third try, but then the loop is stopped. */ + bailout_cnt = 3; + then = loctime; + do { + ltm = localtime(&then); + if (ltm == (struct tm *)NULL || + (tzoffset_adj = loctime - mkgmtime(ltm)) == 0L) + break; + then += tzoffset_adj; + } while (--bailout_cnt > 0); + + if (ltm == (struct tm *)NULL || tzoffset_adj != 0L) { + /* Signal failure if timezone adjustment did not converge. */ + tm->tm_isdst = save_isdst; + return (time_t)-1; + } + + if (save_isdst >= 0) { + if (ltm->tm_isdst && !save_isdst) + { + if (then + 3600 < then) + then = (time_t)-1; + else + then += 3600; + } + else if (!ltm->tm_isdst && save_isdst) + { + if (then - 3600 > then) + then = (time_t)-1; + else + then -= 3600; + } + ltm->tm_isdst = save_isdst; + } + + if (tm != ltm) /* `tm' may already point to localtime's internal storage */ + *tm = *ltm; + + return then; +} + + +#ifndef NO_TIME_T_MAX + /* Provide default values for the upper limit of the time_t range. + These are the result of the decomposition into a `struct tm' for + the time value 0xFFFFFFFEL ( = (time_t)-2 ). + Note: `(time_t)-1' is reserved for "invalid time"! */ +# ifndef TM_YEAR_MAX +# define TM_YEAR_MAX 2106 +# endif +# ifndef TM_MON_MAX +# define TM_MON_MAX 1 /* February */ +# endif +# ifndef TM_MDAY_MAX +# define TM_MDAY_MAX 7 +# endif +# ifndef TM_HOUR_MAX +# define TM_HOUR_MAX 6 +# endif +# ifndef TM_MIN_MAX +# define TM_MIN_MAX 28 +# endif +# ifndef TM_SEC_MAX +# define TM_SEC_MAX 14 +# endif +#endif /* NO_TIME_T_MAX */ + +/* Adjusts out-of-range values for `tm' field `tm_member'. */ +#define ADJUST_TM(tm_member, tm_carry, modulus) \ + if ((tm_member) < 0) { \ + tm_carry -= (1 - ((tm_member)+1) / (modulus)); \ + tm_member = (modulus-1) + (((tm_member)+1) % (modulus)); \ + } else if ((tm_member) >= (modulus)) { \ + tm_carry += (tm_member) / (modulus); \ + tm_member = (tm_member) % (modulus); \ + } + +/* Nonzero if `y' is a leap year, else zero. */ +#define leap(y) (((y) % 4 == 0 && (y) % 100 != 0) || (y) % 400 == 0) + +/* Number of leap years from 1970 to `y' (not including `y' itself). */ +#define nleap(y) (((y) - 1969) / 4 - ((y) - 1901) / 100 + ((y) - 1601) / 400) + +/* Additional leapday in February of leap years. */ +#define leapday(m, y) ((m) == 1 && leap (y)) + +/* Length of month `m' (0 .. 11) */ +#define monthlen(m, y) (ydays[(m)+1] - ydays[m] + leapday (m, y)) + +/* Accumulated number of days from 01-Jan up to start of current month. */ +static ZCONST short ydays[] = +{ + 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 +}; + +/* Return the equivalent in seconds past 12:00:00 a.m. Jan 1, 1970 GMT + of the Greenwich Mean time and date in the exploded time structure `tm'. + This function does always put back normalized values into the `tm' struct, + parameter, including the calculated numbers for `tm->tm_yday', + `tm->tm_wday', and `tm->tm_isdst'. + Returns -1 if the time in the `tm' parameter cannot be represented + as valid `time_t' number. */ + +time_t +mkgmtime(tm) + struct tm *tm; +{ + int years, months, days, hours, minutes, seconds; + + years = tm->tm_year + 1900; /* year - 1900 -> year */ + months = tm->tm_mon; /* 0..11 */ + days = tm->tm_mday - 1; /* 1..31 -> 0..30 */ + hours = tm->tm_hour; /* 0..23 */ + minutes = tm->tm_min; /* 0..59 */ + seconds = tm->tm_sec; /* 0..61 in ANSI C. */ + + ADJUST_TM(seconds, minutes, 60) + ADJUST_TM(minutes, hours, 60) + ADJUST_TM(hours, days, 24) + ADJUST_TM(months, years, 12) + if (days < 0) + do { + if (--months < 0) { + --years; + months = 11; + } + days += monthlen(months, years); + } while (days < 0); + else + while (days >= monthlen(months, years)) { + days -= monthlen(months, years); + if (++months >= 12) { + ++years; + months = 0; + } + } + + /* Restore adjusted values in tm structure */ + tm->tm_year = years - 1900; + tm->tm_mon = months; + tm->tm_mday = days + 1; + tm->tm_hour = hours; + tm->tm_min = minutes; + tm->tm_sec = seconds; + + /* Set `days' to the number of days into the year. */ + days += ydays[months] + (months > 1 && leap (years)); + tm->tm_yday = days; + + /* Now calculate `days' to the number of days since Jan 1, 1970. */ + days = (unsigned)days + 365 * (unsigned)(years - 1970) + + (unsigned)(nleap (years)); + tm->tm_wday = ((unsigned)days + 4) % 7; /* Jan 1, 1970 was Thursday. */ + tm->tm_isdst = 0; + + if (years < 1970) + return (time_t)-1; + +#if (defined(TM_YEAR_MAX) && defined(TM_MON_MAX) && defined(TM_MDAY_MAX)) +#if (defined(TM_HOUR_MAX) && defined(TM_MIN_MAX) && defined(TM_SEC_MAX)) + if (years > TM_YEAR_MAX || + (years == TM_YEAR_MAX && + (tm->tm_yday > ydays[TM_MON_MAX] + (TM_MDAY_MAX - 1) + + (TM_MON_MAX > 1 && leap (TM_YEAR_MAX)) || + (tm->tm_yday == ydays[TM_MON_MAX] + (TM_MDAY_MAX - 1) + + (TM_MON_MAX > 1 && leap (TM_YEAR_MAX)) && + (hours > TM_HOUR_MAX || + (hours == TM_HOUR_MAX && + (minutes > TM_MIN_MAX || + (minutes == TM_MIN_MAX && seconds > TM_SEC_MAX) ))))))) + return (time_t)-1; +#endif +#endif + + return (time_t)(86400L * (unsigned long)(unsigned)days + + 3600L * (unsigned long)hours + + (unsigned long)(60 * minutes + seconds)); +} |