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Diffstat (limited to 'localtime64.c')
| -rw-r--r-- | localtime64.c | 311 |
1 files changed, 311 insertions, 0 deletions
diff --git a/localtime64.c b/localtime64.c new file mode 100644 index 0000000000..92372addd0 --- /dev/null +++ b/localtime64.c @@ -0,0 +1,311 @@ +/* + +Copyright (c) 2007-2008 Michael G Schwern + +This software originally derived from Paul Sheer's pivotal_gmtime_r.c. + +The MIT License: + +Permission is hereby granted, free of charge, to any person obtaining a copy +of this software and associated documentation files (the "Software"), to deal +in the Software without restriction, including without limitation the rights +to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +copies of the Software, and to permit persons to whom the Software is +furnished to do so, subject to the following conditions: + +The above copyright notice and this permission notice shall be included in +all copies or substantial portions of the Software. + +THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN +THE SOFTWARE. + +*/ + +/* + +Programmers who have available to them 64-bit time values as a 'long +long' type can use localtime64_r() and gmtime64_r() which correctly +converts the time even on 32-bit systems. Whether you have 64-bit time +values will depend on the operating system. + +localtime64_r() is a 64-bit equivalent of localtime_r(). + +gmtime64_r() is a 64-bit equivalent of gmtime_r(). + +*/ + +#include <assert.h> +#include <stdlib.h> +#include <stdio.h> +#include <time.h> +#include <errno.h> +#include "localtime64.h" + +static const int days_in_month[2][12] = { + {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, + {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, +}; + +static const int julian_days_by_month[2][12] = { + {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}, + {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}, +}; + +static const int length_of_year[2] = { 365, 366 }; + +/* Number of days in a 400 year Gregorian cycle */ +static const int years_in_gregorian_cycle = 400; +static const int days_in_gregorian_cycle = (365 * 400) + 100 - 4 + 1; + +/* 28 year calendar cycle between 2010 and 2037 */ +static const int safe_years[28] = { + 2016, 2017, 2018, 2019, + 2020, 2021, 2022, 2023, + 2024, 2025, 2026, 2027, + 2028, 2029, 2030, 2031, + 2032, 2033, 2034, 2035, + 2036, 2037, 2010, 2011, + 2012, 2013, 2014, 2015 +}; + +static const int dow_year_start[28] = { + 5, 0, 1, 2, /* 2016 - 2019 */ + 3, 5, 6, 0, + 1, 3, 4, 5, + 6, 1, 2, 3, + 4, 6, 0, 1, + 2, 4, 5, 6, /* 2036, 2037, 2010, 2011 */ + 0, 2, 3, 4 /* 2012, 2013, 2014, 2015 */ +}; + + +#define IS_LEAP(n) ((!(((n) + 1900) % 400) || (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0) +#define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a)) + +int _is_exception_century(long year) +{ + int is_exception = ((year % 100 == 0) && !(year % 400 == 0)); + /* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */ + + return(is_exception); +} + +void _check_tm(struct tm *tm) +{ + /* Don't forget leap seconds */ + assert(tm->tm_sec >= 0 && tm->tm_sec <= 61); + assert(tm->tm_min >= 0 && tm->tm_min <= 59); + assert(tm->tm_hour >= 0 && tm->tm_hour <= 23); + assert(tm->tm_mday >= 1 && tm->tm_mday <= 31); + assert(tm->tm_mon >= 0 && tm->tm_mon <= 11); + assert(tm->tm_wday >= 0 && tm->tm_wday <= 6); + assert(tm->tm_yday >= 0 && tm->tm_yday <= 365); + +#ifdef TM_HAS_GMTOFF + assert( tm->tm_gmtoff >= -24 * 60 * 60 + && tm->tm_gmtoff <= 24 * 60 * 60); +#endif + + if( !IS_LEAP(tm->tm_year) ) { + /* no more than 365 days in a non_leap year */ + assert( tm->tm_yday <= 364 ); + + /* and no more than 28 days in Feb */ + if( tm->tm_mon == 1 ) { + assert( tm->tm_mday <= 28 ); + } + } +} + +/* The exceptional centuries without leap years cause the cycle to + shift by 16 +*/ +int _cycle_offset(long year) +{ + const long start_year = 2000; + long year_diff = year - start_year - 1; + long exceptions = year_diff / 100; + exceptions -= year_diff / 400; + + assert( year >= 2001 ); + + /* printf("year: %d, exceptions: %d\n", year, exceptions); */ + + return exceptions * 16; +} + +/* For a given year after 2038, pick the latest possible matching + year in the 28 year calendar cycle. +*/ +#define SOLAR_CYCLE_LENGTH 28 +int _safe_year(long year) +{ + int safe_year; + long year_cycle = year + _cycle_offset(year); + + /* Change non-leap xx00 years to an equivalent */ + if( _is_exception_century(year) ) + year_cycle += 11; + + year_cycle %= SOLAR_CYCLE_LENGTH; + + safe_year = safe_years[year_cycle]; + + assert(safe_year <= 2037 && safe_year >= 2010); + + /* + printf("year: %d, year_cycle: %d, safe_year: %d\n", + year, year_cycle, safe_year); + */ + + return safe_year; +} + +struct tm *gmtime64_r (const Time64_T *in_time, struct tm *p) +{ + int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday; + Time64_T v_tm_tday; + int leap; + Time64_T m; + Time64_T time = *in_time; + Time64_T year; + +#ifdef TM_HAS_GMTOFF + p->tm_gmtoff = 0; +#endif + p->tm_isdst = 0; + +#ifdef TM_HAS_ZONE + p->tm_zone = "UTC"; +#endif + + v_tm_sec = time % 60; + time /= 60; + v_tm_min = time % 60; + time /= 60; + v_tm_hour = time % 24; + time /= 24; + v_tm_tday = time; + WRAP (v_tm_sec, v_tm_min, 60); + WRAP (v_tm_min, v_tm_hour, 60); + WRAP (v_tm_hour, v_tm_tday, 24); + if ((v_tm_wday = (v_tm_tday + 4) % 7) < 0) + v_tm_wday += 7; + m = v_tm_tday; + if (m >= 0) { + year = 70; + + /* Gregorian cycles, this is huge optimization for distant times */ + while (m >= (Time64_T) days_in_gregorian_cycle) { + m -= (Time64_T) days_in_gregorian_cycle; + year += years_in_gregorian_cycle; + } + + /* Years */ + leap = IS_LEAP (year); + while (m >= (Time64_T) length_of_year[leap]) { + m -= (Time64_T) length_of_year[leap]; + year++; + leap = IS_LEAP (year); + } + + /* Months */ + v_tm_mon = 0; + while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) { + m -= (Time64_T) days_in_month[leap][v_tm_mon]; + v_tm_mon++; + } + } else { + year = 69; + + /* Gregorian cycles */ + while (m < (Time64_T) -days_in_gregorian_cycle) { + m += (Time64_T) days_in_gregorian_cycle; + year -= years_in_gregorian_cycle; + } + + /* Years */ + leap = IS_LEAP (year); + while (m < (Time64_T) -length_of_year[leap]) { + m += (Time64_T) length_of_year[leap]; + year--; + leap = IS_LEAP (year); + } + + /* Months */ + v_tm_mon = 11; + while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) { + m += (Time64_T) days_in_month[leap][v_tm_mon]; + v_tm_mon--; + } + m += (Time64_T) days_in_month[leap][v_tm_mon]; + } + + p->tm_year = year; + if( p->tm_year != year ) { + errno = EOVERFLOW; + return NULL; + } + + p->tm_mday = (int) m + 1; + p->tm_yday = julian_days_by_month[leap][v_tm_mon] + m; + p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour, + p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday; + + _check_tm(p); + + return p; +} + + +struct tm *localtime64_r (const Time64_T *time, struct tm *local_tm) +{ + time_t safe_time; + struct tm gm_tm; + long orig_year; + int month_diff; + + gmtime64_r(time, &gm_tm); + orig_year = gm_tm.tm_year; + + if (gm_tm.tm_year > (2037 - 1900)) + gm_tm.tm_year = _safe_year(gm_tm.tm_year + 1900) - 1900; + + safe_time = timegm(&gm_tm); + localtime_r(&safe_time, local_tm); + + local_tm->tm_year = orig_year; + month_diff = local_tm->tm_mon - gm_tm.tm_mon; + + /* When localtime is Dec 31st previous year and + gmtime is Jan 1st next year. + */ + if( month_diff == 11 ) { + local_tm->tm_year--; + } + + /* When localtime is Jan 1st, next year and + gmtime is Dec 31st, previous year. + */ + if( month_diff == -11 ) { + local_tm->tm_year++; + } + + /* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st + in a non-leap xx00. There is one point in the cycle + we can't account for which the safe xx00 year is a leap + year. So we need to correct for Dec 31st comming out as + the 366th day of the year. + */ + if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 ) + local_tm->tm_yday--; + + _check_tm(local_tm); + + return local_tm; +} |