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). 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. 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