libc/src/time/mktime.cpp

   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_utils.h"
  13
  14 namespace LIBC_NAMESPACE_DECL {
  15
  16 using LIBC_NAMESPACE::time_utils::TimeConstants;
  17
  18 static constexpr int NON_LEAP_YEAR_DAYS_IN_MONTH[] = {31, 28, 31, 30, 31, 30,
  19                                                       31, 31, 30, 31, 30, 31};
  20
  21 // Returns number of years from (1, year).
  22 static constexpr int64_t get_num_of_leap_years_before(int64_t year) {
  23   return (year / 4) - (year / 100) + (year / 400);
  24 }
  25
  26 // Returns True if year is a leap year.
  27 static constexpr bool is_leap_year(const int64_t year) {
  28   return (((year) % 4) == 0 && (((year) % 100) != 0 || ((year) % 400) == 0));
  29 }
  30
  31 LLVM_LIBC_FUNCTION(time_t, mktime, (struct tm * tm_out)) {
  32   // Unlike most C Library functions, mktime doesn't just die on bad input.
  33   // TODO(rtenneti); Handle leap seconds.
  34   int64_t tm_year_from_base = tm_out->tm_year + TimeConstants::TIME_YEAR_BASE;
  35
  36   // 32-bit end-of-the-world is 03:14:07 UTC on 19 January 2038.
  37   if (sizeof(time_t) == 4 &&
  38       tm_year_from_base >= TimeConstants::END_OF32_BIT_EPOCH_YEAR) {
  39     if (tm_year_from_base > TimeConstants::END_OF32_BIT_EPOCH_YEAR)
  40       return time_utils::out_of_range();
  41     if (tm_out->tm_mon > 0)
  42       return time_utils::out_of_range();
  43     if (tm_out->tm_mday > 19)
  44       return time_utils::out_of_range();
  45     else if (tm_out->tm_mday == 19) {
  46       if (tm_out->tm_hour > 3)
  47         return time_utils::out_of_range();
  48       else if (tm_out->tm_hour == 3) {
  49         if (tm_out->tm_min > 14)
  50           return time_utils::out_of_range();
  51         else if (tm_out->tm_min == 14) {
  52           if (tm_out->tm_sec > 7)
  53             return time_utils::out_of_range();
  54         }
  55       }
  56     }
  57   }
  58
  59   // Years are ints.  A 32-bit year will fit into a 64-bit time_t.
  60   // A 64-bit year will not.
  61   static_assert(
  62       sizeof(int) == 4,
  63       "ILP64 is unimplemented. This implementation requires 32-bit integers.");
  64
  65   // Calculate number of months and years from tm_mon.
  66   int64_t month = tm_out->tm_mon;
  67   if (month < 0 || month >= TimeConstants::MONTHS_PER_YEAR - 1) {
  68     int64_t years = month / 12;
  69     month %= 12;
  70     if (month < 0) {
  71       years--;
  72       month += 12;
  73     }
  74     tm_year_from_base += years;
  75   }
  76   bool tm_year_is_leap = is_leap_year(tm_year_from_base);
  77
  78   // Calculate total number of days based on the month and the day (tm_mday).
  79   int64_t total_days = tm_out->tm_mday - 1;
  80   for (int64_t i = 0; i < month; ++i)
  81     total_days += NON_LEAP_YEAR_DAYS_IN_MONTH[i];
  82   // Add one day if it is a leap year and the month is after February.
  83   if (tm_year_is_leap && month > 1)
  84     total_days++;
  85
  86   // Calculate total numbers of days based on the year.
  87   total_days += (tm_year_from_base - TimeConstants::EPOCH_YEAR) *
  88                 TimeConstants::DAYS_PER_NON_LEAP_YEAR;
  89   if (tm_year_from_base >= TimeConstants::EPOCH_YEAR) {
  90     total_days += get_num_of_leap_years_before(tm_year_from_base - 1) -
  91                   get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR);
  92   } else if (tm_year_from_base >= 1) {
  93     total_days -= get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR) -
  94                   get_num_of_leap_years_before(tm_year_from_base - 1);
  95   } else {
  96     // Calculate number of leap years until 0th year.
  97     total_days -= get_num_of_leap_years_before(TimeConstants::EPOCH_YEAR) -
  98                   get_num_of_leap_years_before(0);
  99     if (tm_year_from_base <= 0) {
 100       total_days -= 1; // Subtract 1 for 0th year.
 101       // Calculate number of leap years until -1 year
 102       if (tm_year_from_base < 0) {
 103         total_days -= get_num_of_leap_years_before(-tm_year_from_base) -
 104                       get_num_of_leap_years_before(1);
 105       }
 106     }
 107   }
 108
 109   // TODO(rtenneti): Need to handle timezone and update of tm_isdst.
 110   int64_t seconds = tm_out->tm_sec +
 111                     tm_out->tm_min * TimeConstants::SECONDS_PER_MIN +
 112                     tm_out->tm_hour * TimeConstants::SECONDS_PER_HOUR +
 113                     total_days * TimeConstants::SECONDS_PER_DAY;
 114
 115   // Update the tm structure's year, month, day, etc. from seconds.
 116   if (time_utils::update_from_seconds(seconds, tm_out) < 0)
 117     return time_utils::out_of_range();
 118
 119   return static_cast<time_t>(seconds);
 120 }
 121
 122 } // namespace LIBC_NAMESPACE_DECL