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