//===-- 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/CPP/limits.h" // INT_MIN, INT_MAX
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
namespace LIBC_NAMESPACE_DECL {
namespace time_utils {
using LIBC_NAMESPACE::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 update_from_seconds(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};
constexpr time_t time_min =
(sizeof(time_t) == 4)
? INT_MIN
: INT_MIN * static_cast<int64_t>(
TimeConstants::NUMBER_OF_SECONDS_IN_LEAP_YEAR);
constexpr time_t time_max =
(sizeof(time_t) == 4)
? INT_MAX
: INT_MAX * static_cast<int64_t>(
TimeConstants::NUMBER_OF_SECONDS_IN_LEAP_YEAR);
time_t ts = static_cast<time_t>(total_seconds);
if (ts < time_min || ts > time_max)
return time_utils::out_of_range();
int64_t seconds =
total_seconds - TimeConstants::SECONDS_UNTIL2000_MARCH_FIRST;
int64_t days = seconds / TimeConstants::SECONDS_PER_DAY;
int64_t remainingSeconds = seconds % TimeConstants::SECONDS_PER_DAY;
if (remainingSeconds < 0) {
remainingSeconds += TimeConstants::SECONDS_PER_DAY;
days--;
}
int64_t wday = (TimeConstants::WEEK_DAY_OF2000_MARCH_FIRST + days) %
TimeConstants::DAYS_PER_WEEK;
if (wday < 0)
wday += TimeConstants::DAYS_PER_WEEK;
// Compute the number of 400 year cycles.
int64_t numOfFourHundredYearCycles = days / TimeConstants::DAYS_PER400_YEARS;
int64_t remainingDays = days % TimeConstants::DAYS_PER400_YEARS;
if (remainingDays < 0) {
remainingDays += TimeConstants::DAYS_PER400_YEARS;
numOfFourHundredYearCycles--;
}
// The remaining number of years after computing the number of
// "four hundred year cycles" will be 4 hundred year cycles or less in 400
// years.
int64_t numOfHundredYearCycles = computeRemainingYears(
TimeConstants::DAYS_PER100_YEARS, 4, &remainingDays);
// The remaining number of years after computing the number of
// "hundred year cycles" will be 25 four year cycles or less in 100 years.
int64_t numOfFourYearCycles =
computeRemainingYears(TimeConstants::DAYS_PER4_YEARS, 25, &remainingDays);
// The remaining number of years after computing the number of
// "four year cycles" will be 4 one year cycles or less in 4 years.
int64_t remainingYears = computeRemainingYears(
TimeConstants::DAYS_PER_NON_LEAP_YEAR, 4, &remainingDays);
// Calculate number of years from year 2000.
int64_t years = remainingYears + 4 * numOfFourYearCycles +
100 * numOfHundredYearCycles +
400LL * numOfFourHundredYearCycles;
int leapDay =
!remainingYears && (numOfFourYearCycles || !numOfHundredYearCycles);
// We add 31 and 28 for the number of days in January and February, since our
// starting point was March 1st.
int64_t yday = remainingDays + 31 + 28 + leapDay;
if (yday >= TimeConstants::DAYS_PER_NON_LEAP_YEAR + leapDay)
yday -= TimeConstants::DAYS_PER_NON_LEAP_YEAR + leapDay;
int64_t months = 0;
while (daysInMonth[months] <= remainingDays) {
remainingDays -= daysInMonth[months];
months++;
}
if (months >= TimeConstants::MONTHS_PER_YEAR - 2) {
months -= TimeConstants::MONTHS_PER_YEAR;
years++;
}
if (years > INT_MAX || years < INT_MIN)
return time_utils::out_of_range();
// 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 = static_cast<int>(years + 2000 - TimeConstants::TIME_YEAR_BASE);
tm->tm_mon = static_cast<int>(months + 2);
tm->tm_mday = static_cast<int>(remainingDays + 1);
tm->tm_wday = static_cast<int>(wday);
tm->tm_yday = static_cast<int>(yday);
tm->tm_hour =
static_cast<int>(remainingSeconds / TimeConstants::SECONDS_PER_HOUR);
tm->tm_min =
static_cast<int>(remainingSeconds / TimeConstants::SECONDS_PER_MIN %
TimeConstants::SECONDS_PER_MIN);
tm->tm_sec =
static_cast<int>(remainingSeconds % TimeConstants::SECONDS_PER_MIN);
// TODO(rtenneti): Need to handle timezone and update of tm_isdst.
tm->tm_isdst = 0;
return 0;
}
} // namespace time_utils
} // namespace LIBC_NAMESPACE_DECL
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