src/time/time_utils.h

//===-- Collection of utils for mktime and friends --------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIBC_SRC_TIME_TIME_UTILS_H
#define LLVM_LIBC_SRC_TIME_TIME_UTILS_H

#include "include/errno.h"

#include "src/errno/llvmlibc_errno.h"
#include "src/time/mktime.h"

#include <stdint.h>

namespace __llvm_libc {
namespace time_utils {

struct TimeConstants {
  static constexpr int SecondsPerMin = 60;
  static constexpr int SecondsPerHour = 3600;
  static constexpr int SecondsPerDay = 86400;
  static constexpr int DaysPerWeek = 7;
  static constexpr int MonthsPerYear = 12;
  static constexpr int DaysPerNonLeapYear = 365;
  static constexpr int DaysPerLeapYear = 366;
  static constexpr int TimeYearBase = 1900;
  static constexpr int EpochYear = 1970;
  static constexpr int EpochWeekDay = 4;
  static constexpr int NumberOfSecondsInLeapYear =
      (DaysPerNonLeapYear + 1) * SecondsPerDay;

  /* 2000-03-01 (mod 400 year, immediately after feb29 */
  static constexpr int64_t SecondsUntil2000MarchFirst =
      (946684800LL + SecondsPerDay * (31 + 29));
  static constexpr int WeekDayOf2000MarchFirst = 3;

  static constexpr int DaysPer400Years =
      (DaysPerNonLeapYear * 400 + (400 / 4) - 3);
  static constexpr int DaysPer100Years =
      (DaysPerNonLeapYear * 100 + (100 / 4) - 1);
  static constexpr int DaysPer4Years = (DaysPerNonLeapYear * 4 + 1);

  // The latest time that can be represented in this form is 03:14:07 UTC on
  // Tuesday, 19 January 2038 (corresponding to 2,147,483,647 seconds since the
  // start of the epoch). This means that systems using a 32-bit time_t type are
  // susceptible to the Year 2038 problem.
  static constexpr int EndOf32BitEpochYear = 2038;

  static constexpr time_t OutOfRangeReturnValue = -1;
};

// Update the "tm" structure's year, month, etc. members from seconds.
// "total_seconds" is the number of seconds since January 1st, 1970.
extern int64_t UpdateFromSeconds(int64_t total_seconds, struct tm *tm);

// POSIX.1-2017 requires this.
static inline time_t OutOfRange() {
  llvmlibc_errno = EOVERFLOW;
  return static_cast<time_t>(-1);
}

static inline struct tm *gmtime_internal(const time_t *timer,
                                         struct tm *result) {
  int64_t seconds = *timer;
  // Update the tm structure's year, month, day, etc. from seconds.
  if (UpdateFromSeconds(seconds, result) < 0) {
    OutOfRange();
    return nullptr;
  }

  return result;
}

} // namespace time_utils
} // namespace __llvm_libc

#endif // LLVM_LIBC_SRC_TIME_TIME_UTILS_H