ClickHouse/base/common/DateLUTImpl.cpp

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#include "DateLUTImpl.h"
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#include <cctz/civil_time.h>
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#include <cctz/time_zone.h>
#include <Poco/Exception.h>
#include <cassert>
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#include <chrono>
#include <cstring>
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#include <iostream>
#include <memory>
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#define DATE_LUT_MIN 0
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namespace
{
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UInt8 getDayOfWeek(const cctz::civil_day & date)
{
cctz::weekday day_of_week = cctz::get_weekday(date);
switch (day_of_week)
{
case cctz::weekday::monday: return 1;
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case cctz::weekday::tuesday: return 2;
case cctz::weekday::wednesday: return 3;
case cctz::weekday::thursday: return 4;
case cctz::weekday::friday: return 5;
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case cctz::weekday::saturday: return 6;
case cctz::weekday::sunday: return 7;
default:
throw Poco::Exception("Logical error: incorrect week day.");
}
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}
}
__attribute__((__weak__)) extern bool inside_main;
DateLUTImpl::DateLUTImpl(const std::string & time_zone_)
: time_zone(time_zone_)
{
/// DateLUT should not be initialized in global constructors for the following reasons:
/// 1. It is too heavy.
if (&inside_main)
assert(inside_main);
size_t i = 0;
time_t start_of_day = DATE_LUT_MIN;
cctz::time_zone cctz_time_zone;
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if (!cctz::load_time_zone(time_zone, &cctz_time_zone))
throw Poco::Exception("Cannot load time zone " + time_zone_);
cctz::time_zone::absolute_lookup start_of_epoch_lookup = cctz_time_zone.lookup(std::chrono::system_clock::from_time_t(start_of_day));
offset_at_start_of_epoch = start_of_epoch_lookup.offset;
offset_is_whole_number_of_hours_everytime = true;
cctz::civil_day date{1970, 1, 1};
do
{
cctz::time_zone::civil_lookup lookup = cctz_time_zone.lookup(date);
start_of_day = std::chrono::system_clock::to_time_t(lookup.pre); /// Ambiguity is possible.
Values & values = lut[i];
values.year = date.year();
values.month = date.month();
values.day_of_month = date.day();
values.day_of_week = getDayOfWeek(date);
values.date = start_of_day;
if (values.day_of_month == 1)
{
cctz::civil_month month(date);
values.days_in_month = cctz::civil_day(month + 1) - cctz::civil_day(month);
}
else
values.days_in_month = i != 0 ? lut[i - 1].days_in_month : 31;
values.time_at_offset_change = 0;
values.amount_of_offset_change = 0;
if (start_of_day % 3600)
offset_is_whole_number_of_hours_everytime = false;
/// If UTC offset was changed in previous day.
if (i != 0)
{
auto amount_of_offset_change_at_prev_day = 86400 - (lut[i].date - lut[i - 1].date);
if (amount_of_offset_change_at_prev_day)
{
lut[i - 1].amount_of_offset_change = amount_of_offset_change_at_prev_day;
const auto utc_offset_at_beginning_of_day = cctz_time_zone.lookup(std::chrono::system_clock::from_time_t(lut[i - 1].date)).offset;
/// Find a time (timestamp offset from beginning of day),
/// when UTC offset was changed. Search is performed with 15-minute granularity, assuming it is enough.
time_t time_at_offset_change = 900;
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while (time_at_offset_change < 86400)
{
auto utc_offset_at_current_time = cctz_time_zone.lookup(std::chrono::system_clock::from_time_t(
lut[i - 1].date + time_at_offset_change)).offset;
if (utc_offset_at_current_time != utc_offset_at_beginning_of_day)
break;
time_at_offset_change += 900;
}
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lut[i - 1].time_at_offset_change = time_at_offset_change;
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/// We doesn't support cases when time change results in switching to previous day.
if (static_cast<int>(lut[i - 1].time_at_offset_change) + static_cast<int>(lut[i - 1].amount_of_offset_change) < 0)
lut[i - 1].time_at_offset_change = -lut[i - 1].amount_of_offset_change;
}
}
/// Going to next day.
++date;
++i;
}
while (start_of_day <= DATE_LUT_MAX && i <= DATE_LUT_MAX_DAY_NUM);
/// Fill excessive part of lookup table. This is needed only to simplify handling of overflow cases.
while (i < DATE_LUT_SIZE)
{
lut[i] = lut[DATE_LUT_MAX_DAY_NUM];
++i;
}
/// Fill lookup table for years and months.
size_t year_months_lut_index = 0;
size_t first_day_of_last_month = 0;
for (size_t day = 0; day < DATE_LUT_SIZE; ++day)
{
const Values & values = lut[day];
if (values.day_of_month == 1)
{
if (values.month == 1)
years_lut[values.year - DATE_LUT_MIN_YEAR] = day;
year_months_lut_index = (values.year - DATE_LUT_MIN_YEAR) * 12 + values.month - 1;
years_months_lut[year_months_lut_index] = day;
first_day_of_last_month = day;
}
}
/// Fill the rest of lookup table with the same last month (2106-02-01).
for (; year_months_lut_index < DATE_LUT_YEARS * 12; ++year_months_lut_index)
{
years_months_lut[year_months_lut_index] = first_day_of_last_month;
}
}