1 | //===-- Implementation of mktime function ---------------------------------===// |
2 | // |
3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
4 | // See https://llvm.org/LICENSE.txt for license information. |
5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
6 | // |
7 | //===----------------------------------------------------------------------===// |
8 | |
9 | #include "src/time/time_utils.h" |
10 | #include "src/__support/CPP/limits.h" // INT_MIN, INT_MAX |
11 | #include "src/__support/common.h" |
12 | |
13 | namespace LIBC_NAMESPACE { |
14 | namespace time_utils { |
15 | |
16 | using LIBC_NAMESPACE::time_utils::TimeConstants; |
17 | |
18 | static int64_t computeRemainingYears(int64_t daysPerYears, |
19 | int64_t quotientYears, |
20 | int64_t *remainingDays) { |
21 | int64_t years = *remainingDays / daysPerYears; |
22 | if (years == quotientYears) |
23 | years--; |
24 | *remainingDays -= years * daysPerYears; |
25 | return years; |
26 | } |
27 | |
28 | // First, divide "total_seconds" by the number of seconds in a day to get the |
29 | // number of days since Jan 1 1970. The remainder will be used to calculate the |
30 | // number of Hours, Minutes and Seconds. |
31 | // |
32 | // Then, adjust that number of days by a constant to be the number of days |
33 | // since Mar 1 2000. Year 2000 is a multiple of 400, the leap year cycle. This |
34 | // makes it easier to count how many leap years have passed using division. |
35 | // |
36 | // While calculating numbers of years in the days, the following algorithm |
37 | // subdivides the days into the number of 400 years, the number of 100 years and |
38 | // the number of 4 years. These numbers of cycle years are used in calculating |
39 | // leap day. This is similar to the algorithm used in getNumOfLeapYearsBefore() |
40 | // and isLeapYear(). Then compute the total number of years in days from these |
41 | // subdivided units. |
42 | // |
43 | // Compute the number of months from the remaining days. Finally, adjust years |
44 | // to be 1900 and months to be from January. |
45 | int64_t update_from_seconds(int64_t total_seconds, struct tm *tm) { |
46 | // Days in month starting from March in the year 2000. |
47 | static const char daysInMonth[] = {31 /* Mar */, 30, 31, 30, 31, 31, |
48 | 30, 31, 30, 31, 31, 29}; |
49 | |
50 | constexpr time_t time_min = |
51 | (sizeof(time_t) == 4) |
52 | ? INT_MIN |
53 | : INT_MIN * static_cast<int64_t>( |
54 | TimeConstants::NUMBER_OF_SECONDS_IN_LEAP_YEAR); |
55 | constexpr time_t time_max = |
56 | (sizeof(time_t) == 4) |
57 | ? INT_MAX |
58 | : INT_MAX * static_cast<int64_t>( |
59 | TimeConstants::NUMBER_OF_SECONDS_IN_LEAP_YEAR); |
60 | |
61 | time_t ts = static_cast<time_t>(total_seconds); |
62 | if (ts < time_min || ts > time_max) |
63 | return time_utils::out_of_range(); |
64 | |
65 | int64_t seconds = |
66 | total_seconds - TimeConstants::SECONDS_UNTIL2000_MARCH_FIRST; |
67 | int64_t days = seconds / TimeConstants::SECONDS_PER_DAY; |
68 | int64_t remainingSeconds = seconds % TimeConstants::SECONDS_PER_DAY; |
69 | if (remainingSeconds < 0) { |
70 | remainingSeconds += TimeConstants::SECONDS_PER_DAY; |
71 | days--; |
72 | } |
73 | |
74 | int64_t wday = (TimeConstants::WEEK_DAY_OF2000_MARCH_FIRST + days) % |
75 | TimeConstants::DAYS_PER_WEEK; |
76 | if (wday < 0) |
77 | wday += TimeConstants::DAYS_PER_WEEK; |
78 | |
79 | // Compute the number of 400 year cycles. |
80 | int64_t numOfFourHundredYearCycles = days / TimeConstants::DAYS_PER400_YEARS; |
81 | int64_t remainingDays = days % TimeConstants::DAYS_PER400_YEARS; |
82 | if (remainingDays < 0) { |
83 | remainingDays += TimeConstants::DAYS_PER400_YEARS; |
84 | numOfFourHundredYearCycles--; |
85 | } |
86 | |
87 | // The remaining number of years after computing the number of |
88 | // "four hundred year cycles" will be 4 hundred year cycles or less in 400 |
89 | // years. |
90 | int64_t numOfHundredYearCycles = computeRemainingYears( |
91 | daysPerYears: TimeConstants::DAYS_PER100_YEARS, quotientYears: 4, remainingDays: &remainingDays); |
92 | |
93 | // The remaining number of years after computing the number of |
94 | // "hundred year cycles" will be 25 four year cycles or less in 100 years. |
95 | int64_t numOfFourYearCycles = |
96 | computeRemainingYears(daysPerYears: TimeConstants::DAYS_PER4_YEARS, quotientYears: 25, remainingDays: &remainingDays); |
97 | |
98 | // The remaining number of years after computing the number of |
99 | // "four year cycles" will be 4 one year cycles or less in 4 years. |
100 | int64_t remainingYears = computeRemainingYears( |
101 | daysPerYears: TimeConstants::DAYS_PER_NON_LEAP_YEAR, quotientYears: 4, remainingDays: &remainingDays); |
102 | |
103 | // Calculate number of years from year 2000. |
104 | int64_t years = remainingYears + 4 * numOfFourYearCycles + |
105 | 100 * numOfHundredYearCycles + |
106 | 400LL * numOfFourHundredYearCycles; |
107 | |
108 | int leapDay = |
109 | !remainingYears && (numOfFourYearCycles || !numOfHundredYearCycles); |
110 | |
111 | // We add 31 and 28 for the number of days in January and February, since our |
112 | // starting point was March 1st. |
113 | int64_t yday = remainingDays + 31 + 28 + leapDay; |
114 | if (yday >= TimeConstants::DAYS_PER_NON_LEAP_YEAR + leapDay) |
115 | yday -= TimeConstants::DAYS_PER_NON_LEAP_YEAR + leapDay; |
116 | |
117 | int64_t months = 0; |
118 | while (daysInMonth[months] <= remainingDays) { |
119 | remainingDays -= daysInMonth[months]; |
120 | months++; |
121 | } |
122 | |
123 | if (months >= TimeConstants::MONTHS_PER_YEAR - 2) { |
124 | months -= TimeConstants::MONTHS_PER_YEAR; |
125 | years++; |
126 | } |
127 | |
128 | if (years > INT_MAX || years < INT_MIN) |
129 | return time_utils::out_of_range(); |
130 | |
131 | // All the data (years, month and remaining days) was calculated from |
132 | // March, 2000. Thus adjust the data to be from January, 1900. |
133 | tm->tm_year = static_cast<int>(years + 2000 - TimeConstants::TIME_YEAR_BASE); |
134 | tm->tm_mon = static_cast<int>(months + 2); |
135 | tm->tm_mday = static_cast<int>(remainingDays + 1); |
136 | tm->tm_wday = static_cast<int>(wday); |
137 | tm->tm_yday = static_cast<int>(yday); |
138 | |
139 | tm->tm_hour = |
140 | static_cast<int>(remainingSeconds / TimeConstants::SECONDS_PER_HOUR); |
141 | tm->tm_min = |
142 | static_cast<int>(remainingSeconds / TimeConstants::SECONDS_PER_MIN % |
143 | TimeConstants::SECONDS_PER_MIN); |
144 | tm->tm_sec = |
145 | static_cast<int>(remainingSeconds % TimeConstants::SECONDS_PER_MIN); |
146 | // TODO(rtenneti): Need to handle timezone and update of tm_isdst. |
147 | tm->tm_isdst = 0; |
148 | |
149 | return 0; |
150 | } |
151 | |
152 | } // namespace time_utils |
153 | } // namespace LIBC_NAMESPACE |
154 | |