1 | /* |
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2 | * gmtime_r.c |
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3 | * Original Author: Adapted from tzcode maintained by Arthur David Olson. |
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4 | * Modifications: |
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5 | * - Changed to mktm_r and added __tzcalc_limits - 04/10/02, Jeff Johnston |
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6 | * - Fixed bug in mday computations - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru> |
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7 | * - Fixed bug in __tzcalc_limits - 08/12/04, Alex Mogilnikov <alx@intellectronika.ru> |
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8 | * - Move code from _mktm_r() to gmtime_r() - 05/09/14, Freddie Chopin <freddie_chopin@op.pl> |
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9 | * - Fixed bug in calculations for dates after year 2069 or before year 1901. Ideas for |
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10 | * solution taken from musl's __secs_to_tm() - 07/12/2014, Freddie Chopin |
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11 | * <freddie_chopin@op.pl> |
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12 | * - Use faster algorithm from civil_from_days() by Howard Hinnant - 12/06/2014, |
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13 | * Freddie Chopin <freddie_chopin@op.pl> |
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14 | * |
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15 | * Converts the calendar time pointed to by tim_p into a broken-down time |
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16 | * expressed as local time. Returns a pointer to a structure containing the |
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17 | * broken-down time. |
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18 | */ |
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19 | |
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20 | #include "local.h" |
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21 | |
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22 | /* Move epoch from 01.01.1970 to 01.03.0000 (yes, Year 0) - this is the first |
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23 | * day of a 400-year long "era", right after additional day of leap year. |
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24 | * This adjustment is required only for date calculation, so instead of |
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25 | * modifying time_t value (which would require 64-bit operations to work |
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26 | * correctly) it's enough to adjust the calculated number of days since epoch. |
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27 | */ |
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28 | #define EPOCH_ADJUSTMENT_DAYS 719468L |
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29 | /* year to which the adjustment was made */ |
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30 | #define ADJUSTED_EPOCH_YEAR 0 |
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31 | /* 1st March of year 0 is Wednesday */ |
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32 | #define ADJUSTED_EPOCH_WDAY 3 |
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33 | /* there are 97 leap years in 400-year periods. ((400 - 97) * 365 + 97 * 366) */ |
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34 | #define DAYS_PER_ERA 146097L |
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35 | /* there are 24 leap years in 100-year periods. ((100 - 24) * 365 + 24 * 366) */ |
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36 | #define DAYS_PER_CENTURY 36524L |
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37 | /* there is one leap year every 4 years */ |
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38 | #define DAYS_PER_4_YEARS (3 * 365 + 366) |
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39 | /* number of days in a non-leap year */ |
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40 | #define DAYS_PER_YEAR 365 |
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41 | /* number of days in January */ |
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42 | #define DAYS_IN_JANUARY 31 |
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43 | /* number of days in non-leap February */ |
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44 | #define DAYS_IN_FEBRUARY 28 |
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45 | /* number of years per era */ |
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46 | #define YEARS_PER_ERA 400 |
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47 | |
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48 | struct tm * |
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49 | gmtime_r (const time_t *__restrict tim_p, |
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50 | struct tm *__restrict res) |
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51 | { |
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52 | long days, rem; |
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53 | const time_t lcltime = *tim_p; |
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54 | int era, weekday, year; |
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55 | unsigned erayear, yearday, month, day; |
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56 | unsigned long eraday; |
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57 | |
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58 | days = lcltime / SECSPERDAY + EPOCH_ADJUSTMENT_DAYS; |
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59 | rem = lcltime % SECSPERDAY; |
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60 | if (rem < 0) |
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61 | { |
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62 | rem += SECSPERDAY; |
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63 | --days; |
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64 | } |
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65 | |
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66 | /* compute hour, min, and sec */ |
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67 | res->tm_hour = (int) (rem / SECSPERHOUR); |
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68 | rem %= SECSPERHOUR; |
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69 | res->tm_min = (int) (rem / SECSPERMIN); |
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70 | res->tm_sec = (int) (rem % SECSPERMIN); |
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71 | |
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72 | /* compute day of week */ |
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73 | if ((weekday = ((ADJUSTED_EPOCH_WDAY + days) % DAYSPERWEEK)) < 0) |
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74 | weekday += DAYSPERWEEK; |
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75 | res->tm_wday = weekday; |
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76 | |
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77 | /* compute year, month, day & day of year */ |
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78 | /* for description of this algorithm see |
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79 | * http://howardhinnant.github.io/date_algorithms.html#civil_from_days */ |
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80 | era = (days >= 0 ? days : days - (DAYS_PER_ERA - 1)) / DAYS_PER_ERA; |
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81 | eraday = days - era * DAYS_PER_ERA; /* [0, 146096] */ |
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82 | erayear = (eraday - eraday / (DAYS_PER_4_YEARS - 1) + eraday / DAYS_PER_CENTURY - |
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83 | eraday / (DAYS_PER_ERA - 1)) / 365; /* [0, 399] */ |
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84 | yearday = eraday - (DAYS_PER_YEAR * erayear + erayear / 4 - erayear / 100); /* [0, 365] */ |
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85 | month = (5 * yearday + 2) / 153; /* [0, 11] */ |
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86 | day = yearday - (153 * month + 2) / 5 + 1; /* [1, 31] */ |
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87 | month += month < 10 ? 2 : -10; |
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88 | year = ADJUSTED_EPOCH_YEAR + erayear + era * YEARS_PER_ERA + (month <= 1); |
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89 | |
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90 | res->tm_yday = yearday >= DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY ? |
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91 | yearday - (DAYS_PER_YEAR - DAYS_IN_JANUARY - DAYS_IN_FEBRUARY) : |
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92 | yearday + DAYS_IN_JANUARY + DAYS_IN_FEBRUARY + isleap(erayear); |
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93 | res->tm_year = year - YEAR_BASE; |
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94 | res->tm_mon = month; |
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95 | res->tm_mday = day; |
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96 | |
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97 | res->tm_isdst = 0; |
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98 | |
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99 | return (res); |
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100 | } |
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