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_constants.h" 13 #include "src/time/time_utils.h" 14 15 namespace LIBC_NAMESPACE_DECL { 16 17 // Returns number of years from (1, year). 18 static constexpr int64_t get_num_of_leap_years_before(int64_t year) { 19 return (year / 4) - (year / 100) + (year / 400); 20 } 21 22 // Returns True if year is a leap year. 23 static constexpr bool is_leap_year(const int64_t year) { 24 return (((year) % 4) == 0 && (((year) % 100) != 0 || ((year) % 400) == 0)); 25 } 26 27 LLVM_LIBC_FUNCTION(time_t, mktime, (struct tm * tm_out)) { 28 // Unlike most C Library functions, mktime doesn't just die on bad input. 29 // TODO(rtenneti); Handle leap seconds. 30 int64_t tm_year_from_base = tm_out->tm_year + time_constants::TIME_YEAR_BASE; 31 32 // 32-bit end-of-the-world is 03:14:07 UTC on 19 January 2038. 33 if (sizeof(time_t) == 4 && 34 tm_year_from_base >= time_constants::END_OF32_BIT_EPOCH_YEAR) { 35 if (tm_year_from_base > time_constants::END_OF32_BIT_EPOCH_YEAR) 36 return time_utils::out_of_range(); 37 if (tm_out->tm_mon > 0) 38 return time_utils::out_of_range(); 39 if (tm_out->tm_mday > 19) 40 return time_utils::out_of_range(); 41 else if (tm_out->tm_mday == 19) { 42 if (tm_out->tm_hour > 3) 43 return time_utils::out_of_range(); 44 else if (tm_out->tm_hour == 3) { 45 if (tm_out->tm_min > 14) 46 return time_utils::out_of_range(); 47 else if (tm_out->tm_min == 14) { 48 if (tm_out->tm_sec > 7) 49 return time_utils::out_of_range(); 50 } 51 } 52 } 53 } 54 55 // Years are ints. A 32-bit year will fit into a 64-bit time_t. 56 // A 64-bit year will not. 57 static_assert( 58 sizeof(int) == 4, 59 "ILP64 is unimplemented. This implementation requires 32-bit integers."); 60 61 // Calculate number of months and years from tm_mon. 62 int64_t month = tm_out->tm_mon; 63 if (month < 0 || month >= time_constants::MONTHS_PER_YEAR - 1) { 64 int64_t years = month / 12; 65 month %= 12; 66 if (month < 0) { 67 years--; 68 month += 12; 69 } 70 tm_year_from_base += years; 71 } 72 bool tm_year_is_leap = is_leap_year(tm_year_from_base); 73 74 // Calculate total number of days based on the month and the day (tm_mday). 75 int64_t total_days = tm_out->tm_mday - 1; 76 for (int64_t i = 0; i < month; ++i) 77 total_days += time_constants::NON_LEAP_YEAR_DAYS_IN_MONTH[i]; 78 // Add one day if it is a leap year and the month is after February. 79 if (tm_year_is_leap && month > 1) 80 total_days++; 81 82 // Calculate total numbers of days based on the year. 83 total_days += (tm_year_from_base - time_constants::EPOCH_YEAR) * 84 time_constants::DAYS_PER_NON_LEAP_YEAR; 85 if (tm_year_from_base >= time_constants::EPOCH_YEAR) { 86 total_days += get_num_of_leap_years_before(tm_year_from_base - 1) - 87 get_num_of_leap_years_before(time_constants::EPOCH_YEAR); 88 } else if (tm_year_from_base >= 1) { 89 total_days -= get_num_of_leap_years_before(time_constants::EPOCH_YEAR) - 90 get_num_of_leap_years_before(tm_year_from_base - 1); 91 } else { 92 // Calculate number of leap years until 0th year. 93 total_days -= get_num_of_leap_years_before(time_constants::EPOCH_YEAR) - 94 get_num_of_leap_years_before(0); 95 if (tm_year_from_base <= 0) { 96 total_days -= 1; // Subtract 1 for 0th year. 97 // Calculate number of leap years until -1 year 98 if (tm_year_from_base < 0) { 99 total_days -= get_num_of_leap_years_before(-tm_year_from_base) - 100 get_num_of_leap_years_before(1); 101 } 102 } 103 } 104 105 // TODO: https://github.com/llvm/llvm-project/issues/121962 106 // Need to handle timezone and update of tm_isdst. 107 int64_t seconds = tm_out->tm_sec + 108 tm_out->tm_min * time_constants::SECONDS_PER_MIN + 109 tm_out->tm_hour * time_constants::SECONDS_PER_HOUR + 110 total_days * time_constants::SECONDS_PER_DAY; 111 112 // Update the tm structure's year, month, day, etc. from seconds. 113 if (time_utils::update_from_seconds(seconds, tm_out) < 0) 114 return time_utils::out_of_range(); 115 116 return static_cast<time_t>(seconds); 117 } 118 119 } // namespace LIBC_NAMESPACE_DECL 120