1 | #include "time_impl.h"
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2 | #include <limits.h>
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3 |
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4 | /* 2000-03-01 (mod 400 year, immediately after feb29 */
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5 | #define LEAPOCH (946684800LL + 86400*(31+29))
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6 |
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7 | #define DAYS_PER_400Y (365*400 + 97)
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8 | #define DAYS_PER_100Y (365*100 + 24)
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9 | #define DAYS_PER_4Y (365*4 + 1)
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10 |
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11 | int __secs_to_tm(long long t, struct tm *tm)
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12 | {
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13 | long long days, secs, years;
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14 | int remdays, remsecs, remyears;
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15 | int qc_cycles, c_cycles, q_cycles;
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16 | int months;
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17 | int wday, yday, leap;
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18 | static const char days_in_month[] = {31,30,31,30,31,31,30,31,30,31,31,29};
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19 |
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20 | /* Reject time_t values whose year would overflow int */
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21 | if (t < INT_MIN * 31622400LL || t > INT_MAX * 31622400LL)
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22 | return -1;
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23 |
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24 | secs = t - LEAPOCH;
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25 | days = secs / 86400;
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26 | remsecs = secs % 86400;
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27 | if (remsecs < 0) {
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28 | remsecs += 86400;
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29 | days--;
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30 | }
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31 |
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32 | wday = (3+days)%7;
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33 | if (wday < 0) wday += 7;
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34 |
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35 | qc_cycles = days / DAYS_PER_400Y;
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36 | remdays = days % DAYS_PER_400Y;
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37 | if (remdays < 0) {
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38 | remdays += DAYS_PER_400Y;
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39 | qc_cycles--;
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40 | }
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41 |
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42 | c_cycles = remdays / DAYS_PER_100Y;
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43 | if (c_cycles == 4) c_cycles--;
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44 | remdays -= c_cycles * DAYS_PER_100Y;
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45 |
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46 | q_cycles = remdays / DAYS_PER_4Y;
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47 | if (q_cycles == 25) q_cycles--;
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48 | remdays -= q_cycles * DAYS_PER_4Y;
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49 |
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50 | remyears = remdays / 365;
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51 | if (remyears == 4) remyears--;
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52 | remdays -= remyears * 365;
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53 |
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54 | leap = !remyears && (q_cycles || !c_cycles);
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55 | yday = remdays + 31 + 28 + leap;
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56 | if (yday >= 365+leap) yday -= 365+leap;
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57 |
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58 | years = remyears + 4*q_cycles + 100*c_cycles + 400LL*qc_cycles;
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59 |
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60 | for (months=0; days_in_month[months] <= remdays; months++)
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61 | remdays -= days_in_month[months];
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62 |
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63 | if (months >= 10) {
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64 | months -= 12;
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65 | years++;
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66 | }
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67 |
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68 | if (years+100 > INT_MAX || years+100 < INT_MIN)
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69 | return -1;
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70 |
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71 | tm->tm_year = years + 100;
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72 | tm->tm_mon = months + 2;
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73 | tm->tm_mday = remdays + 1;
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74 | tm->tm_wday = wday;
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75 | tm->tm_yday = yday;
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76 |
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77 | tm->tm_hour = remsecs / 3600;
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78 | tm->tm_min = remsecs / 60 % 60;
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79 | tm->tm_sec = remsecs % 60;
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80 |
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81 | return 0;
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82 | }
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