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/mktime.h"
10 #include "src/__support/common.h"
11 #include "src/__support/macros/config.h"
12 #include "src/time/time_utils.h"
13
14 namespace LIBC_NAMESPACE_DECL {
15
16 using LIBC_NAMESPACE::time_utils::TimeConstants;
17
18 static constexpr int NON_LEAP_YEAR_DAYS_IN_MONTH[] = {31, 28, 31, 30, 31, 30,
19 31, 31, 30, 31, 30, 31};
20
21 // Returns number of years from (1, year).
get_num_of_leap_years_before(int64_t year)22 static constexpr int64_t get_num_of_leap_years_before(int64_t year) {
23 return (year / 4) - (year / 100) + (year / 400);
24 }
25
26 // Returns True if year is a leap year.
is_leap_year(const int64_t year)27 static constexpr bool is_leap_year(const int64_t year) {
28 return (((year) % 4) == 0 && (((year) % 100) != 0 || ((year) % 400) == 0));
29 }
30
31 LLVM_LIBC_FUNCTION(time_t, mktime, (struct tm * tm_out)) {
32 // Unlike most C Library functions, mktime doesn't just die on bad input.
33 // TODO(rtenneti); Handle leap seconds.
34 int64_t tm_year_from_base = tm_out->tm_year + TimeConstants::TIME_YEAR_BASE;
35
36 // 32-bit end-of-the-world is 03:14:07 UTC on 19 January 2038.
37 if (sizeof(time_t) == 4 &&
38 tm_year_from_base >= TimeConstants::END_OF32_BIT_EPOCH_YEAR) {
39 if (tm_year_from_base > TimeConstants::END_OF32_BIT_EPOCH_YEAR)
40 return time_utils::out_of_range();
41 if (tm_out->tm_mon > 0)
42 return time_utils::out_of_range();
43 if (tm_out->tm_mday > 19)
44 return time_utils::out_of_range();
45 else if (tm_out->tm_mday == 19) {
46 if (tm_out->tm_hour > 3)
47 return time_utils::out_of_range();
48 else if (tm_out->tm_hour == 3) {
49 if (tm_out->tm_min > 14)
50 return time_utils::out_of_range();
51 else if (tm_out->tm_min == 14) {
52 if (tm_out->tm_sec > 7)
53 return time_utils::out_of_range();
54 }
55 }
56 }
57 }
58
59 // Years are ints. A 32-bit year will fit into a 64-bit time_t.
60 // A 64-bit year will not.
61 static_assert(
62 sizeof(int) == 4,
63 "ILP64 is unimplemented. This implementation requires 32-bit integers.");
64
65 // Calculate number of months and years from tm_mon.
66 int64_t month = tm_out->tm_mon;
67 if (month < 0 || month >= TimeConstants::MONTHS_PER_YEAR - 1) {
68 int64_t years = month / 12;
69 month %= 12;
70 if (month < 0) {
71 years--;
72 month += 12;
73 }
74 tm_year_from_base += years;
75 }
76 bool tm_year_is_leap = is_leap_year(tm_year_from_base);
77
78 // Calculate total number of days based on the month and the day (tm_mday).
79 int64_t total_days = tm_out->tm_mday - 1;
80 for (int64_t i = 0; i < month; ++i)
81 total_days += NON_LEAP_YEAR_DAYS_IN_MONTH[i];
82 // Add one day if it is a leap year and the month is after February.
83 if (tm_year_is_leap && month > 1)
84 total_days++;
85
86 // Calculate total numbers of days based on the year.
87 total_days += (tm_year_from_base - TimeConstants::EPOCH_YEAR) *
88 TimeConstants::DAYS_PER_NON_LEAP_YEAR;
89 if (tm_year_from_base >= TimeConstants::EPOCH_YEAR) {
90 total_days += get_num_of_leap_years_before(tm_year_from_base - 1) -
91 get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR);
92 } else if (tm_year_from_base >= 1) {
93 total_days -= get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR) -
94 get_num_of_leap_years_before(tm_year_from_base - 1);
95 } else {
96 // Calculate number of leap years until 0th year.
97 total_days -= get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR) -
98 get_num_of_leap_years_before(0);
99 if (tm_year_from_base <= 0) {
100 total_days -= 1; // Subtract 1 for 0th year.
101 // Calculate number of leap years until -1 year
102 if (tm_year_from_base < 0) {
103 total_days -= get_num_of_leap_years_before(-tm_year_from_base) -
104 get_num_of_leap_years_before(1);
105 }
106 }
107 }
108
109 // TODO(rtenneti): Need to handle timezone and update of tm_isdst.
110 int64_t seconds = tm_out->tm_sec +
111 tm_out->tm_min * TimeConstants::SECONDS_PER_MIN +
112 tm_out->tm_hour * TimeConstants::SECONDS_PER_HOUR +
113 total_days * TimeConstants::SECONDS_PER_DAY;
114
115 // Update the tm structure's year, month, day, etc. from seconds.
116 if (time_utils::update_from_seconds(seconds, tm_out) < 0)
117 return time_utils::out_of_range();
118
119 return static_cast<time_t>(seconds);
120 }
121
122 } // namespace LIBC_NAMESPACE_DECL
123