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#include "src/__support/macros/config.h"
13#include "src/time/time_constants.h"
14
15#include <stdint.h>
16
17namespace LIBC_NAMESPACE_DECL {
18namespace time_utils {
19
20// TODO: clean this up in a followup patch
21cpp::optional<time_t> mktime_internal(const tm *tm_out) {
22 // Unlike most C Library functions, mktime doesn't just die on bad input.
23 // TODO(rtenneti); Handle leap seconds.
24 int64_t tm_year_from_base = tm_out->tm_year + time_constants::TIME_YEAR_BASE;
25
26 // 32-bit end-of-the-world is 03:14:07 UTC on 19 January 2038.
27 if (sizeof(time_t) == 4 &&
28 tm_year_from_base >= time_constants::END_OF32_BIT_EPOCH_YEAR) {
29 if (tm_year_from_base > time_constants::END_OF32_BIT_EPOCH_YEAR)
30 return cpp::nullopt;
31 if (tm_out->tm_mon > 0)
32 return cpp::nullopt;
33 if (tm_out->tm_mday > 19)
34 return cpp::nullopt;
35 else if (tm_out->tm_mday == 19) {
36 if (tm_out->tm_hour > 3)
37 return cpp::nullopt;
38 else if (tm_out->tm_hour == 3) {
39 if (tm_out->tm_min > 14)
40 return cpp::nullopt;
41 else if (tm_out->tm_min == 14) {
42 if (tm_out->tm_sec > 7)
43 return cpp::nullopt;
44 }
45 }
46 }
47 }
48
49 // Years are ints. A 32-bit year will fit into a 64-bit time_t.
50 // A 64-bit year will not.
51 static_assert(
52 sizeof(int) == 4,
53 "ILP64 is unimplemented. This implementation requires 32-bit integers.");
54
55 // Calculate number of months and years from tm_mon.
56 int64_t month = tm_out->tm_mon;
57 if (month < 0 || month >= time_constants::MONTHS_PER_YEAR - 1) {
58 int64_t years = month / 12;
59 month %= 12;
60 if (month < 0) {
61 years--;
62 month += 12;
63 }
64 tm_year_from_base += years;
65 }
66 bool tm_year_is_leap = time_utils::is_leap_year(tm_year_from_base);
67
68 // Calculate total number of days based on the month and the day (tm_mday).
69 int64_t total_days = tm_out->tm_mday - 1;
70 for (int64_t i = 0; i < month; ++i)
71 total_days += time_constants::NON_LEAP_YEAR_DAYS_IN_MONTH[i];
72 // Add one day if it is a leap year and the month is after February.
73 if (tm_year_is_leap && month > 1)
74 total_days++;
75
76 // Calculate total numbers of days based on the year.
77 total_days += (tm_year_from_base - time_constants::EPOCH_YEAR) *
78 time_constants::DAYS_PER_NON_LEAP_YEAR;
79 if (tm_year_from_base >= time_constants::EPOCH_YEAR) {
80 total_days +=
81 time_utils::get_num_of_leap_years_before(tm_year_from_base - 1) -
82 time_utils::get_num_of_leap_years_before(time_constants::EPOCH_YEAR);
83 } else if (tm_year_from_base >= 1) {
84 total_days -=
85 time_utils::get_num_of_leap_years_before(time_constants::EPOCH_YEAR) -
86 time_utils::get_num_of_leap_years_before(tm_year_from_base - 1);
87 } else {
88 // Calculate number of leap years until 0th year.
89 total_days -=
90 time_utils::get_num_of_leap_years_before(time_constants::EPOCH_YEAR) -
91 time_utils::get_num_of_leap_years_before(0);
92 if (tm_year_from_base <= 0) {
93 total_days -= 1; // Subtract 1 for 0th year.
94 // Calculate number of leap years until -1 year
95 if (tm_year_from_base < 0) {
96 total_days -=
97 time_utils::get_num_of_leap_years_before(-tm_year_from_base) -
98 time_utils::get_num_of_leap_years_before(1);
99 }
100 }
101 }
102
103 // TODO: https://github.com/llvm/llvm-project/issues/121962
104 // Need to handle timezone and update of tm_isdst.
105 time_t seconds = static_cast<time_t>(
106 tm_out->tm_sec + tm_out->tm_min * time_constants::SECONDS_PER_MIN +
107 tm_out->tm_hour * time_constants::SECONDS_PER_HOUR +
108 total_days * time_constants::SECONDS_PER_DAY);
109 return seconds;
110}
111
112static int64_t computeRemainingYears(int64_t daysPerYears,
113 int64_t quotientYears,
114 int64_t *remainingDays) {
115 int64_t years = *remainingDays / daysPerYears;
116 if (years == quotientYears)
117 years--;
118 *remainingDays -= years * daysPerYears;
119 return years;
120}
121
122// First, divide "total_seconds" by the number of seconds in a day to get the
123// number of days since Jan 1 1970. The remainder will be used to calculate the
124// number of Hours, Minutes and Seconds.
125//
126// Then, adjust that number of days by a constant to be the number of days
127// since Mar 1 2000. Year 2000 is a multiple of 400, the leap year cycle. This
128// makes it easier to count how many leap years have passed using division.
129//
130// While calculating numbers of years in the days, the following algorithm
131// subdivides the days into the number of 400 years, the number of 100 years and
132// the number of 4 years. These numbers of cycle years are used in calculating
133// leap day. This is similar to the algorithm used in getNumOfLeapYearsBefore()
134// and isLeapYear(). Then compute the total number of years in days from these
135// subdivided units.
136//
137// Compute the number of months from the remaining days. Finally, adjust years
138// to be 1900 and months to be from January.
139int64_t update_from_seconds(time_t total_seconds, tm *tm) {
140 // Days in month starting from March in the year 2000.
141 static const char daysInMonth[] = {31 /* Mar */, 30, 31, 30, 31, 31,
142 30, 31, 30, 31, 31, 29};
143
144 constexpr time_t time_min =
145 (sizeof(time_t) == 4)
146 ? INT_MIN
147 : INT_MIN * static_cast<int64_t>(
148 time_constants::NUMBER_OF_SECONDS_IN_LEAP_YEAR);
149 constexpr time_t time_max =
150 (sizeof(time_t) == 4)
151 ? INT_MAX
152 : INT_MAX * static_cast<int64_t>(
153 time_constants::NUMBER_OF_SECONDS_IN_LEAP_YEAR);
154
155 if (total_seconds < time_min || total_seconds > time_max)
156 return time_utils::out_of_range();
157
158 int64_t seconds =
159 total_seconds - time_constants::SECONDS_UNTIL2000_MARCH_FIRST;
160 int64_t days = seconds / time_constants::SECONDS_PER_DAY;
161 int64_t remainingSeconds = seconds % time_constants::SECONDS_PER_DAY;
162 if (remainingSeconds < 0) {
163 remainingSeconds += time_constants::SECONDS_PER_DAY;
164 days--;
165 }
166
167 int64_t wday = (time_constants::WEEK_DAY_OF2000_MARCH_FIRST + days) %
168 time_constants::DAYS_PER_WEEK;
169 if (wday < 0)
170 wday += time_constants::DAYS_PER_WEEK;
171
172 // Compute the number of 400 year cycles.
173 int64_t numOfFourHundredYearCycles = days / time_constants::DAYS_PER400_YEARS;
174 int64_t remainingDays = days % time_constants::DAYS_PER400_YEARS;
175 if (remainingDays < 0) {
176 remainingDays += time_constants::DAYS_PER400_YEARS;
177 numOfFourHundredYearCycles--;
178 }
179
180 // The remaining number of years after computing the number of
181 // "four hundred year cycles" will be 4 hundred year cycles or less in 400
182 // years.
183 int64_t numOfHundredYearCycles = computeRemainingYears(
184 time_constants::DAYS_PER100_YEARS, 4, &remainingDays);
185
186 // The remaining number of years after computing the number of
187 // "hundred year cycles" will be 25 four year cycles or less in 100 years.
188 int64_t numOfFourYearCycles = computeRemainingYears(
189 time_constants::DAYS_PER4_YEARS, 25, &remainingDays);
190
191 // The remaining number of years after computing the number of
192 // "four year cycles" will be 4 one year cycles or less in 4 years.
193 int64_t remainingYears = computeRemainingYears(
194 time_constants::DAYS_PER_NON_LEAP_YEAR, 4, &remainingDays);
195
196 // Calculate number of years from year 2000.
197 int64_t years = remainingYears + 4 * numOfFourYearCycles +
198 100 * numOfHundredYearCycles +
199 400LL * numOfFourHundredYearCycles;
200
201 int leapDay =
202 !remainingYears && (numOfFourYearCycles || !numOfHundredYearCycles);
203
204 // We add 31 and 28 for the number of days in January and February, since our
205 // starting point was March 1st.
206 int64_t yday = remainingDays + 31 + 28 + leapDay;
207 if (yday >= time_constants::DAYS_PER_NON_LEAP_YEAR + leapDay)
208 yday -= time_constants::DAYS_PER_NON_LEAP_YEAR + leapDay;
209
210 int64_t months = 0;
211 while (daysInMonth[months] <= remainingDays) {
212 remainingDays -= daysInMonth[months];
213 months++;
214 }
215
216 if (months >= time_constants::MONTHS_PER_YEAR - 2) {
217 months -= time_constants::MONTHS_PER_YEAR;
218 years++;
219 }
220
221 if (years > INT_MAX || years < INT_MIN)
222 return time_utils::out_of_range();
223
224 // All the data (years, month and remaining days) was calculated from
225 // March, 2000. Thus adjust the data to be from January, 1900.
226 tm->tm_year = static_cast<int>(years + 2000 - time_constants::TIME_YEAR_BASE);
227 tm->tm_mon = static_cast<int>(months + 2);
228 tm->tm_mday = static_cast<int>(remainingDays + 1);
229 tm->tm_wday = static_cast<int>(wday);
230 tm->tm_yday = static_cast<int>(yday);
231
232 tm->tm_hour =
233 static_cast<int>(remainingSeconds / time_constants::SECONDS_PER_HOUR);
234 tm->tm_min =
235 static_cast<int>(remainingSeconds / time_constants::SECONDS_PER_MIN %
236 time_constants::SECONDS_PER_MIN);
237 tm->tm_sec =
238 static_cast<int>(remainingSeconds % time_constants::SECONDS_PER_MIN);
239 // TODO(rtenneti): Need to handle timezone and update of tm_isdst.
240 tm->tm_isdst = 0;
241
242 return 0;
243}
244
245} // namespace time_utils
246} // namespace LIBC_NAMESPACE_DECL
247

source code of libc/src/time/time_utils.cpp