1 /*
2 * Copyright (c) 2019 Peter Bigot Consulting, LLC
3 *
4 * SPDX-License-Identifier: Apache-2.0
5 */
6
7 /*
8 * The time_civil_from_days function is derived directly from public
9 * domain content written by Howard Hinnant and available at:
10 * http://howardhinnant.github.io/date_algorithms.html#civil_from_days
11 */
12
13 #include <time.h>
14
15 /* A signed type with the representation of time_t without its
16 * impliciations.
17 */
18 typedef time_t bigint_type;
19
20 /** Convert a UNIX time to civil time.
21 *
22 * This converts integral seconds since (before) 1970-01-01T00:00:00
23 * to the POSIX standard civil time representation. Any adjustments
24 * due to time zone, leap seconds, or a different epoch must be
25 * applied to @p time before invoking this function.
26 *
27 * @param time the time represented as seconds.
28 *
29 * @return the time information for corresponding to the provided
30 * instant.
31 *
32 * @see http://howardhinnant.github.io/date_algorithms.html#civil_from_days
33 */
time_civil_from_days(bigint_type z,struct tm * _MLIBC_RESTRICT tp)34 static void time_civil_from_days(bigint_type z,
35 struct tm *_MLIBC_RESTRICT tp)
36 {
37 tp->tm_wday = (z >= -4) ? ((z + 4) % 7) : ((z + 5) % 7 + 6);
38 z += 719468;
39
40 bigint_type era = ((z >= 0) ? z : (z - 146096)) / 146097;
41 unsigned int doe = (z - era * (bigint_type)146097);
42 unsigned int yoe = (doe - doe / 1460U + doe / 36524U - doe / 146096U)
43 / 365U;
44 bigint_type y = (time_t)yoe + era * 400;
45 unsigned int doy = doe - (365U * yoe + yoe / 4U - yoe / 100U);
46 unsigned int mp = (5U * doy + 2U) / 153U;
47 unsigned int d = doy - (153U * mp + 2U) / 5U + 1U;
48 unsigned int m = mp + ((mp < 10) ? 3 : -9);
49
50 tp->tm_year = y + (m <= 2) - 1900;
51 tp->tm_mon = m - 1;
52 tp->tm_mday = d;
53
54 /* Everything above is explained on the referenced page, but
55 * doy is relative to --03-01 and we need it relative to
56 * --01-01.
57 *
58 * doy=306 corresponds to --01-01, doy=364 to --02-28, and
59 * doy=365 to --02-29. So we can just subtract 306 to handle
60 * January and February.
61 *
62 * For doy<306 we have to add the number of days before
63 * --03-01, which is 59 in a common year and 60 in a leap
64 * year. Note that the first year in the era is a leap year.
65 */
66 if (doy >= 306U) {
67 tp->tm_yday = doy - 306U;
68 } else {
69 tp->tm_yday = doy + 59U + (((yoe % 4U == 0U) && (yoe % 100U != 0U)) || (yoe == 0U));
70 }
71 }
72
73 /* Convert a UNIX time to civil time.
74 *
75 * This converts integral seconds since (before) 1970-01-01T00:00:00
76 * to the POSIX standard civil time representation. Any adjustments
77 * due to time zone, leap seconds, or a different epoch must be
78 * applied to @p time before invoking this function.
79 */
gmtime_r(const time_t * _MLIBC_RESTRICT timep,struct tm * _MLIBC_RESTRICT result)80 struct tm *gmtime_r(const time_t *_MLIBC_RESTRICT timep,
81 struct tm *_MLIBC_RESTRICT result)
82 {
83 time_t z = *timep;
84 bigint_type days = (z >= 0 ? z : z - 86399) / 86400;
85 unsigned int rem = z - days * 86400;
86
87 *result = (struct tm){ 0 };
88
89 time_civil_from_days(days, result);
90
91 result->tm_hour = rem / 60U / 60U;
92 rem -= result->tm_hour * 60 * 60;
93 result->tm_min = rem / 60;
94 result->tm_sec = rem - result->tm_min * 60;
95
96 return result;
97 }
98
gmtime(const time_t * timep)99 struct tm *gmtime(const time_t *timep)
100 {
101 static struct tm shared;
102
103 return gmtime_r(timep, &shared);
104 }
105
