diff options
Diffstat (limited to 'libc/misc/time/mktime.c')
| -rw-r--r-- | libc/misc/time/mktime.c | 259 |
1 files changed, 259 insertions, 0 deletions
diff --git a/libc/misc/time/mktime.c b/libc/misc/time/mktime.c new file mode 100644 index 000000000..7f7aabcd7 --- /dev/null +++ b/libc/misc/time/mktime.c @@ -0,0 +1,259 @@ + +/* This is adapted from glibc */ +/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc. */ + + +/* Assume that leap seconds are possible, unless told otherwise. + If the host has a `zic' command with a -L leapsecondfilename' option, + then it supports leap seconds; otherwise it probably doesn't. */ +#ifndef LEAP_SECONDS_POSSIBLE +#define LEAP_SECONDS_POSSIBLE 1 +#endif + +#include <sys/types.h> /* Some systems define `time_t' here. */ +#include <time.h> + +#if __STDC__ || __GNU_LIBRARY__ || STDC_HEADERS +#include <limits.h> +#endif + +#if DEBUG +#include <stdio.h> +#if __STDC__ || __GNU_LIBRARY__ || STDC_HEADERS +#include <stdlib.h> +#endif +/* Make it work even if the system's libc has its own mktime routine. */ +#define mktime my_mktime +#endif /* DEBUG */ + +#ifndef __P +#if defined (__GNUC__) || (defined (__STDC__) && __STDC__) +#define __P(args) args +#else +#define __P(args) () +#endif /* GCC. */ +#endif /* Not __P. */ + +#ifndef CHAR_BIT +#define CHAR_BIT 8 +#endif + +#ifndef INT_MIN +#define INT_MIN (~0 << (sizeof (int) * CHAR_BIT - 1)) +#endif +#ifndef INT_MAX +#define INT_MAX (~0 - INT_MIN) +#endif + +#ifndef TIME_T_MIN +#define TIME_T_MIN (0 < (time_t) -1 ? (time_t) 0 \ + : ~ (time_t) 0 << (sizeof (time_t) * CHAR_BIT - 1)) +#endif +#ifndef TIME_T_MAX +#define TIME_T_MAX (~ (time_t) 0 - TIME_T_MIN) +#endif + +#define TM_YEAR_BASE 1900 +#define EPOCH_YEAR 1970 + +#ifndef __isleap +/* Nonzero if YEAR is a leap year (every 4 years, + except every 100th isn't, and every 400th is). */ +#define __isleap(year) \ + ((year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0)) +#endif + +/* How many days come before each month (0-12). */ +const unsigned short int __mon_yday[2][13] = + { + /* Normal years. */ + { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 }, + /* Leap years. */ + { 0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366 } + }; + +static time_t ydhms_tm_diff __P ((int, int, int, int, int, const struct tm *)); +time_t __mktime_internal __P ((struct tm *, + struct tm *(*) (const time_t *, struct tm *), + time_t *)); + +/* Yield the difference between (YEAR-YDAY HOUR:MIN:SEC) and (*TP), + measured in seconds, ignoring leap seconds. + YEAR uses the same numbering as TM->tm_year. + All values are in range, except possibly YEAR. + If overflow occurs, yield the low order bits of the correct answer. */ +static time_t +ydhms_tm_diff (year, yday, hour, min, sec, tp) + int year, yday, hour, min, sec; + const struct tm *tp; +{ + /* Compute intervening leap days correctly even if year is negative. + Take care to avoid int overflow. time_t overflow is OK, since + only the low order bits of the correct time_t answer are needed. + Don't convert to time_t until after all divisions are done, since + time_t might be unsigned. */ + int a4 = (year >> 2) + (TM_YEAR_BASE >> 2) - ! (year & 3); + int b4 = (tp->tm_year >> 2) + (TM_YEAR_BASE >> 2) - ! (tp->tm_year & 3); + int a100 = a4 / 25 - (a4 % 25 < 0); + int b100 = b4 / 25 - (b4 % 25 < 0); + int a400 = a100 >> 2; + int b400 = b100 >> 2; + int intervening_leap_days = (a4 - b4) - (a100 - b100) + (a400 - b400); + time_t years = year - (time_t) tp->tm_year; + time_t days = (365 * years + intervening_leap_days + + (yday - tp->tm_yday)); + return (60 * (60 * (24 * days + (hour - tp->tm_hour)) + + (min - tp->tm_min)) + + (sec - tp->tm_sec)); +} + + +static time_t localtime_offset; + + +/* Convert *TP to a time_t value. */ +time_t +mktime (tp) + struct tm *tp; +{ +#ifdef _LIBC + /* POSIX.1 8.1.1 requires that whenever mktime() is called, the + time zone names contained in the external variable `tzname' shall + be set as if the tzset() function had been called. */ + __tzset (); +#endif + + return __mktime_internal (tp, localtime_r, &localtime_offset); +} + +/* Convert *TP to a time_t value, inverting + the monotonic and mostly-unit-linear conversion function CONVERT. + Use *OFFSET to keep track of a guess at the offset of the result, + compared to what the result would be for UTC without leap seconds. + If *OFFSET's guess is correct, only one CONVERT call is needed. */ +time_t +__mktime_internal (tp, convert, offset) + struct tm *tp; + struct tm *(*convert) __P ((const time_t *, struct tm *)); + time_t *offset; +{ + time_t t, dt, t0; + struct tm tm; + + /* The maximum number of probes (calls to CONVERT) should be enough + to handle any combinations of time zone rule changes, solar time, + and leap seconds. Posix.1 prohibits leap seconds, but some hosts + have them anyway. */ + int remaining_probes = 4; + + /* Time requested. Copy it in case CONVERT modifies *TP; this can + occur if TP is localtime's returned value and CONVERT is localtime. */ + int sec = tp->tm_sec; + int min = tp->tm_min; + int hour = tp->tm_hour; + int mday = tp->tm_mday; + int mon = tp->tm_mon; + int year_requested = tp->tm_year; + int isdst = tp->tm_isdst; + + /* Ensure that mon is in range, and set year accordingly. */ + int mon_remainder = mon % 12; + int negative_mon_remainder = mon_remainder < 0; + int mon_years = mon / 12 - negative_mon_remainder; + int year = year_requested + mon_years; + + /* The other values need not be in range: + the remaining code handles minor overflows correctly, + assuming int and time_t arithmetic wraps around. + Major overflows are caught at the end. */ + + /* Calculate day of year from year, month, and day of month. + The result need not be in range. */ + int yday = ((__mon_yday[__isleap (year + TM_YEAR_BASE)] + [mon_remainder + 12 * negative_mon_remainder]) + + mday - 1); + +#if LEAP_SECONDS_POSSIBLE + /* Handle out-of-range seconds specially, + since ydhms_tm_diff assumes every minute has 60 seconds. */ + int sec_requested = sec; + if (sec < 0) + sec = 0; + if (59 < sec) + sec = 59; +#endif + + /* Invert CONVERT by probing. First assume the same offset as last time. + Then repeatedly use the error to improve the guess. */ + + tm.tm_year = EPOCH_YEAR - TM_YEAR_BASE; + tm.tm_yday = tm.tm_hour = tm.tm_min = tm.tm_sec = 0; + t0 = ydhms_tm_diff (year, yday, hour, min, sec, &tm); + + for (t = t0 + *offset; + (dt = ydhms_tm_diff (year, yday, hour, min, sec, (*convert) (&t, &tm))); + t += dt) + if (--remaining_probes == 0) + return -1; + + /* Check whether tm.tm_isdst has the requested value, if any. */ + if (0 <= isdst && 0 <= tm.tm_isdst) + { + int dst_diff = (isdst != 0) - (tm.tm_isdst != 0); + if (dst_diff) + { + /* Move two hours in the direction indicated by the disagreement, + probe some more, and switch to a new time if found. + The largest known fallback due to daylight savings is two hours: + once, in Newfoundland, 1988-10-30 02:00 -> 00:00. */ + time_t ot = t - 2 * 60 * 60 * dst_diff; + while (--remaining_probes != 0) + { + struct tm otm; + if (! (dt = ydhms_tm_diff (year, yday, hour, min, sec, + (*convert) (&ot, &otm)))) + { + t = ot; + tm = otm; + break; + } + if ((ot += dt) == t) + break; /* Avoid a redundant probe. */ + } + } + } + + *offset = t - t0; + +#if LEAP_SECONDS_POSSIBLE + if (sec_requested != tm.tm_sec) + { + /* Adjust time to reflect the tm_sec requested, not the normalized value. + Also, repair any damage from a false match due to a leap second. */ + t += sec_requested - sec + (sec == 0 && tm.tm_sec == 60); + (*convert) (&t, &tm); + } +#endif + +#if 0 + if (TIME_T_MAX / INT_MAX / 366 / 24 / 60 / 60 < 3) + { + /* time_t isn't large enough to rule out overflows in ydhms_tm_diff, + so check for major overflows. A gross check suffices, + since if t has overflowed, it is off by a multiple of + TIME_T_MAX - TIME_T_MIN + 1. So ignore any component of + the difference that is bounded by a small value. */ + + double dyear = (double) year_requested + mon_years - tm.tm_year; + double dday = 366 * dyear + mday; + double dsec = 60 * (60 * (24 * dday + hour) + min) + sec_requested; + + if (TIME_T_MAX / 3 - TIME_T_MIN / 3 < (dsec < 0 ? - dsec : dsec)) + return -1; + } +#endif + + *tp = tm; + return t; +} + |