| #ifndef DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
| #define DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__ |
| |
| /* Copyright (c) 2002,2003 CrystalClear Software, Inc. |
| * Use, modification and distribution is subject to the |
| * Boost Software License, Version 1.0. (See accompanying |
| * file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt) |
| * Author: Jeff Garland |
| * $Date: 2008-11-12 14:37:53 -0500 (Wed, 12 Nov 2008) $ |
| */ |
| |
| /*! @file local_time_adjustor.hpp |
| Time adjustment calculations for local times |
| */ |
| |
| #include <stdexcept> |
| #include <boost/throw_exception.hpp> |
| #include <boost/date_time/compiler_config.hpp> |
| #include <boost/date_time/date_generators.hpp> |
| #include <boost/date_time/dst_rules.hpp> |
| #include <boost/date_time/time_defs.hpp> // boost::date_time::dst_flags |
| #include <boost/date_time/special_defs.hpp> // not_a_date_time |
| |
| namespace boost { |
| namespace date_time { |
| |
| |
| //! Provides a base offset adjustment from utc |
| template<class time_duration_type, |
| short hours, unsigned short minutes = 0> |
| class utc_adjustment |
| { |
| public: |
| static time_duration_type local_to_utc_base_offset() |
| { |
| time_duration_type td(hours,minutes,0); |
| return td.invert_sign(); |
| } |
| static time_duration_type utc_to_local_base_offset() |
| { |
| return time_duration_type(hours,minutes,0); |
| } |
| }; |
| |
| |
| |
| //! Allow sliding utc adjustment with fixed dst rules |
| template<class time_type, class dst_rules> |
| class dynamic_local_time_adjustor : public dst_rules |
| { |
| public: |
| typedef typename time_type::time_duration_type time_duration_type; |
| typedef typename time_type::date_type date_type; |
| |
| dynamic_local_time_adjustor(time_duration_type utc_offset) : |
| utc_offset_(utc_offset) |
| {} |
| |
| //! Presumes local time |
| time_duration_type utc_offset(bool is_dst) |
| { |
| if (is_dst) { |
| return utc_offset_ + this->dst_offset(); |
| } |
| else { |
| return utc_offset_; |
| } |
| |
| } |
| private: |
| time_duration_type utc_offset_; |
| |
| }; |
| |
| |
| |
| //! Embed the rules for local time adjustments at compile time |
| template<class time_type, class dst_rules, class utc_offset_rules> |
| class static_local_time_adjustor: public dst_rules, public utc_offset_rules |
| { |
| public: |
| typedef typename time_type::time_duration_type time_duration_type; |
| typedef typename time_type::date_type date_type; |
| |
| //! Calculates the offset from a utc time to local based on dst and utc offset |
| /*! @param t UTC time to calculate offset to local time |
| * This adjustment depends on the following observations about the |
| * workings of the DST boundary offset. Since UTC time labels are |
| * monotonically increasing we can determine if a given local time |
| * is in DST or not and therefore adjust the offset appropriately. |
| * |
| * The logic is as follows. Starting with UTC time use the offset to |
| * create a label for an non-dst adjusted local time. Then call |
| * dst_rules::local_is_dst with the non adjust local time. The |
| * results of this function will either unabiguously decide that |
| * the initial local time is in dst or return an illegal or |
| * ambiguous result. An illegal result only occurs at the end |
| * of dst (where labels are skipped) and indicates that dst has |
| * ended. An ambiguous result means that we need to recheck by |
| * making a dst adjustment and then rechecking. If the dst offset |
| * is added to the utc time and the recheck proves non-ambiguous |
| * then we are past the boundary. If it is still ambiguous then |
| * we are ahead of the boundary and dst is still in effect. |
| * |
| * TODO -- check if all dst offsets are positive. If not then |
| * the algorithm needs to check for this and reverse the |
| * illegal/ambiguous logic. |
| */ |
| static time_duration_type utc_to_local_offset(const time_type& t) |
| { |
| //get initial local time guess by applying utc offset |
| time_type initial = t + utc_offset_rules::utc_to_local_base_offset(); |
| time_is_dst_result dst_flag = |
| dst_rules::local_is_dst(initial.date(), initial.time_of_day()); |
| switch(dst_flag) { |
| case is_in_dst: return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
| case is_not_in_dst: return utc_offset_rules::utc_to_local_base_offset(); |
| case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
| case ambiguous: { |
| time_type retry = initial + dst_rules::dst_offset(); |
| dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day()); |
| //if still ambibuous then the utc time still translates to a dst time |
| if (dst_flag == ambiguous) { |
| return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset(); |
| } |
| // we are past the dst boundary |
| else { |
| return utc_offset_rules::utc_to_local_base_offset(); |
| } |
| } |
| }//case |
| //TODO better exception type |
| boost::throw_exception(std::out_of_range("Unreachable case")); |
| BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
| } |
| |
| //! Get the offset to UTC given a local time |
| static time_duration_type local_to_utc_offset(const time_type& t, |
| date_time::dst_flags dst=date_time::calculate) |
| { |
| switch (dst) { |
| case is_dst: |
| return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
| case not_dst: |
| return utc_offset_rules::local_to_utc_base_offset(); |
| case calculate: |
| time_is_dst_result res = |
| dst_rules::local_is_dst(t.date(), t.time_of_day()); |
| switch(res) { |
| case is_in_dst: return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset(); |
| case is_not_in_dst: return utc_offset_rules::local_to_utc_base_offset(); |
| case ambiguous: return utc_offset_rules::local_to_utc_base_offset(); |
| case invalid_time_label: break; |
| } |
| } |
| boost::throw_exception(std::out_of_range("Time label invalid")); |
| BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach |
| } |
| |
| |
| private: |
| |
| }; |
| |
| void dummy_to_prevent_msvc6_ice(); //why ask why? |
| |
| //! Template that simplifies the creation of local time calculator |
| /*! Use this template to create the timezone to utc convertors as required. |
| * |
| * This class will also work for other regions that don't use dst and |
| * have a utc offset which is an integral number of hours. |
| * |
| * <b>Template Parameters</b> |
| * -time_type -- Time class to use |
| * -utc_offset -- Number hours local time is adjust from utc |
| * -use_dst -- true (default) if region uses dst, false otherwise |
| * For example: |
| * @code |
| * //eastern timezone is utc-5 |
| typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern; |
| typedef date_time::local_adjustor<ptime, -6, us_dst> us_central; |
| typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain; |
| typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific; |
| typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona; |
| @endcode |
| |
| */ |
| template<class time_type, short utc_offset, class dst_rule> |
| class local_adjustor |
| { |
| public: |
| typedef typename time_type::time_duration_type time_duration_type; |
| typedef typename time_type::date_type date_type; |
| typedef static_local_time_adjustor<time_type, |
| dst_rule, |
| utc_adjustment<time_duration_type, |
| utc_offset> > dst_adjustor; |
| //! Convert a utc time to local time |
| static time_type utc_to_local(const time_type& t) |
| { |
| time_duration_type td = dst_adjustor::utc_to_local_offset(t); |
| return t + td; |
| } |
| //! Convert a local time to utc |
| static time_type local_to_utc(const time_type& t, |
| date_time::dst_flags dst=date_time::calculate) |
| { |
| time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst); |
| return t + td; |
| } |
| }; |
| |
| |
| } } //namespace date_time |
| |
| |
| |
| #endif |