blob: 11ac2fb0d9a0b7dfa3733026e01a7a9df9113335 [file] [log] [blame]
 //===-- Implementation of mktime function ---------------------------------===// // // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. // See https://llvm.org/LICENSE.txt for license information. // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception // //===----------------------------------------------------------------------===// #include "src/time/time_utils.h" #include "src/__support/common.h" #include namespace __llvm_libc { namespace time_utils { using __llvm_libc::time_utils::TimeConstants; static int64_t computeRemainingYears(int64_t daysPerYears, int64_t quotientYears, int64_t *remainingDays) { int64_t years = *remainingDays / daysPerYears; if (years == quotientYears) years--; *remainingDays -= years * daysPerYears; return years; } // First, divide "total_seconds" by the number of seconds in a day to get the // number of days since Jan 1 1970. The remainder will be used to calculate the // number of Hours, Minutes and Seconds. // // Then, adjust that number of days by a constant to be the number of days // since Mar 1 2000. Year 2000 is a multiple of 400, the leap year cycle. This // makes it easier to count how many leap years have passed using division. // // While calculating numbers of years in the days, the following algorithm // subdivides the days into the number of 400 years, the number of 100 years and // the number of 4 years. These numbers of cycle years are used in calculating // leap day. This is similar to the algorithm used in getNumOfLeapYearsBefore() // and isLeapYear(). Then compute the total number of years in days from these // subdivided units. // // Compute the number of months from the remaining days. Finally, adjust years // to be 1900 and months to be from January. int64_t UpdateFromSeconds(int64_t total_seconds, struct tm *tm) { // Days in month starting from March in the year 2000. static const char daysInMonth[] = {31 /* Mar */, 30, 31, 30, 31, 31, 30, 31, 30, 31, 31, 29}; if (sizeof(time_t) == 4) { if (total_seconds < 0x80000000) return time_utils::OutOfRange(); if (total_seconds > 0x7FFFFFFF) return time_utils::OutOfRange(); } else { if (total_seconds < INT_MIN * static_cast( TimeConstants::NumberOfSecondsInLeapYear) || total_seconds > INT_MAX * static_cast( TimeConstants::NumberOfSecondsInLeapYear)) return time_utils::OutOfRange(); } int64_t seconds = total_seconds - TimeConstants::SecondsUntil2000MarchFirst; int64_t days = seconds / TimeConstants::SecondsPerDay; int64_t remainingSeconds = seconds % TimeConstants::SecondsPerDay; if (remainingSeconds < 0) { remainingSeconds += TimeConstants::SecondsPerDay; days--; } int64_t wday = (TimeConstants::WeekDayOf2000MarchFirst + days) % TimeConstants::DaysPerWeek; if (wday < 0) wday += TimeConstants::DaysPerWeek; // Compute the number of 400 year cycles. int64_t numOfFourHundredYearCycles = days / TimeConstants::DaysPer400Years; int64_t remainingDays = days % TimeConstants::DaysPer400Years; if (remainingDays < 0) { remainingDays += TimeConstants::DaysPer400Years; numOfFourHundredYearCycles--; } // The reminder number of years after computing number of // "four hundred year cycles" will be 4 hundred year cycles or less in 400 // years. int64_t numOfHundredYearCycles = computeRemainingYears(TimeConstants::DaysPer100Years, 4, &remainingDays); // The reminder number of years after computing number of // "hundred year cycles" will be 25 four year cycles or less in 100 years. int64_t numOfFourYearCycles = computeRemainingYears(TimeConstants::DaysPer4Years, 25, &remainingDays); // The reminder number of years after computing number of "four year cycles" // will be 4 one year cycles or less in 4 years. int64_t remainingYears = computeRemainingYears( TimeConstants::DaysPerNonLeapYear, 4, &remainingDays); // Calculate number of years from year 2000. int64_t years = remainingYears + 4 * numOfFourYearCycles + 100 * numOfHundredYearCycles + 400LL * numOfFourHundredYearCycles; int leapDay = !remainingYears && (numOfFourYearCycles || !numOfHundredYearCycles); int64_t yday = remainingDays + 31 + 28 + leapDay; if (yday >= TimeConstants::DaysPerNonLeapYear + leapDay) yday -= TimeConstants::DaysPerNonLeapYear + leapDay; int64_t months = 0; while (daysInMonth[months] <= remainingDays) { remainingDays -= daysInMonth[months]; months++; } if (months >= TimeConstants::MonthsPerYear - 2) { months -= TimeConstants::MonthsPerYear; years++; } if (years > INT_MAX || years < INT_MIN) return time_utils::OutOfRange(); // All the data (years, month and remaining days) was calculated from // March, 2000. Thus adjust the data to be from January, 1900. tm->tm_year = years + 2000 - TimeConstants::TimeYearBase; tm->tm_mon = months + 2; tm->tm_mday = remainingDays + 1; tm->tm_wday = wday; tm->tm_yday = yday; tm->tm_hour = remainingSeconds / TimeConstants::SecondsPerHour; tm->tm_min = remainingSeconds / TimeConstants::SecondsPerMin % TimeConstants::SecondsPerMin; tm->tm_sec = remainingSeconds % TimeConstants::SecondsPerMin; // TODO(rtenneti): Need to handle timezone and update of tm_isdst. tm->tm_isdst = 0; return 0; } } // namespace time_utils } // namespace __llvm_libc