1#ifndef DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__
2#define DATE_TIME_LOCAL_TIME_ADJUSTOR_HPP__
3
4/* Copyright (c) 2002,2003 CrystalClear Software, Inc.
5 * Use, modification and distribution is subject to the
6 * Boost Software License, Version 1.0. (See accompanying
7 * file LICENSE_1_0.txt or http://www.boost.org/LICENSE_1_0.txt)
8 * Author: Jeff Garland
9 * $Date$
10 */
11
12/*! @file local_time_adjustor.hpp
13 Time adjustment calculations for local times
14*/
15
16#include <stdexcept>
17#include <boost/throw_exception.hpp>
18#include <boost/date_time/compiler_config.hpp>
19#include <boost/date_time/date_generators.hpp>
20#include <boost/date_time/dst_rules.hpp>
21#include <boost/date_time/time_defs.hpp> // boost::date_time::dst_flags
22#include <boost/date_time/special_defs.hpp> // not_a_date_time
23
24namespace boost {
25 namespace date_time {
26
27
28 //! Provides a base offset adjustment from utc
29 template<class time_duration_type,
30 short hours, unsigned short minutes = 0>
31 class utc_adjustment
32 {
33 public:
34 static time_duration_type local_to_utc_base_offset()
35 {
36 time_duration_type td(hours,minutes,0);
37 return td.invert_sign();
38 }
39 static time_duration_type utc_to_local_base_offset()
40 {
41 return time_duration_type(hours,minutes,0);
42 }
43 };
44
45
46
47 //! Allow sliding utc adjustment with fixed dst rules
48 template<class time_type, class dst_rules>
49 class dynamic_local_time_adjustor : public dst_rules
50 {
51 public:
52 typedef typename time_type::time_duration_type time_duration_type;
53 typedef typename time_type::date_type date_type;
54
55 dynamic_local_time_adjustor(time_duration_type utc_offset) :
56 utc_offset_(utc_offset)
57 {}
58
59 //! Presumes local time
60 time_duration_type utc_offset(bool is_dst)
61 {
62 if (is_dst) {
63 return utc_offset_ + this->dst_offset();
64 }
65 else {
66 return utc_offset_;
67 }
68
69 }
70 private:
71 time_duration_type utc_offset_;
72
73 };
74
75
76
77 //! Embed the rules for local time adjustments at compile time
78 template<class time_type, class dst_rules, class utc_offset_rules>
79 class static_local_time_adjustor: public dst_rules, public utc_offset_rules
80 {
81 public:
82 typedef typename time_type::time_duration_type time_duration_type;
83 typedef typename time_type::date_type date_type;
84
85 //! Calculates the offset from a utc time to local based on dst and utc offset
86 /*! @param t UTC time to calculate offset to local time
87 * This adjustment depends on the following observations about the
88 * workings of the DST boundary offset. Since UTC time labels are
89 * monotonically increasing we can determine if a given local time
90 * is in DST or not and therefore adjust the offset appropriately.
91 *
92 * The logic is as follows. Starting with UTC time use the offset to
93 * create a label for an non-dst adjusted local time. Then call
94 * dst_rules::local_is_dst with the non adjust local time. The
95 * results of this function will either unabiguously decide that
96 * the initial local time is in dst or return an illegal or
97 * ambiguous result. An illegal result only occurs at the end
98 * of dst (where labels are skipped) and indicates that dst has
99 * ended. An ambiguous result means that we need to recheck by
100 * making a dst adjustment and then rechecking. If the dst offset
101 * is added to the utc time and the recheck proves non-ambiguous
102 * then we are past the boundary. If it is still ambiguous then
103 * we are ahead of the boundary and dst is still in effect.
104 *
105 * TODO -- check if all dst offsets are positive. If not then
106 * the algorithm needs to check for this and reverse the
107 * illegal/ambiguous logic.
108 */
109 static time_duration_type utc_to_local_offset(const time_type& t)
110 {
111 //get initial local time guess by applying utc offset
112 time_type initial = t + utc_offset_rules::utc_to_local_base_offset();
113 time_is_dst_result dst_flag =
114 dst_rules::local_is_dst(initial.date(), initial.time_of_day());
115 switch(dst_flag) {
116 case is_in_dst: return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
117 case is_not_in_dst: return utc_offset_rules::utc_to_local_base_offset();
118 case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
119 case ambiguous: {
120 time_type retry = initial + dst_rules::dst_offset();
121 dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day());
122 //if still ambibuous then the utc time still translates to a dst time
123 if (dst_flag == ambiguous) {
124 return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
125 }
126 // we are past the dst boundary
127 else {
128 return utc_offset_rules::utc_to_local_base_offset();
129 }
130 }
131 }//case
132 //TODO better exception type
133 boost::throw_exception(e: std::out_of_range("Unreachable case"));
134 BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach
135 }
136
137 //! Get the offset to UTC given a local time
138 static time_duration_type local_to_utc_offset(const time_type& t,
139 date_time::dst_flags dst=date_time::calculate)
140 {
141 switch (dst) {
142 case is_dst:
143 return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
144 case not_dst:
145 return utc_offset_rules::local_to_utc_base_offset();
146 case calculate:
147 time_is_dst_result res =
148 dst_rules::local_is_dst(t.date(), t.time_of_day());
149 switch(res) {
150 case is_in_dst: return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
151 case is_not_in_dst: return utc_offset_rules::local_to_utc_base_offset();
152 case ambiguous: return utc_offset_rules::local_to_utc_base_offset();
153 case invalid_time_label: break;
154 }
155 }
156 boost::throw_exception(e: std::out_of_range("Time label invalid"));
157 BOOST_DATE_TIME_UNREACHABLE_EXPRESSION(return time_duration_type(not_a_date_time)); // should never reach
158 }
159
160
161 private:
162
163 };
164
165 void dummy_to_prevent_msvc6_ice(); //why ask why?
166
167 //! Template that simplifies the creation of local time calculator
168 /*! Use this template to create the timezone to utc convertors as required.
169 *
170 * This class will also work for other regions that don't use dst and
171 * have a utc offset which is an integral number of hours.
172 *
173 * <b>Template Parameters</b>
174 * -time_type -- Time class to use
175 * -utc_offset -- Number hours local time is adjust from utc
176 * -use_dst -- true (default) if region uses dst, false otherwise
177 * For example:
178 * @code
179 * //eastern timezone is utc-5
180 typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern;
181 typedef date_time::local_adjustor<ptime, -6, us_dst> us_central;
182 typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain;
183 typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific;
184 typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona;
185 @endcode
186
187 */
188 template<class time_type, short utc_offset, class dst_rule>
189 class local_adjustor
190 {
191 public:
192 typedef typename time_type::time_duration_type time_duration_type;
193 typedef typename time_type::date_type date_type;
194 typedef static_local_time_adjustor<time_type,
195 dst_rule,
196 utc_adjustment<time_duration_type,
197 utc_offset> > dst_adjustor;
198 //! Convert a utc time to local time
199 static time_type utc_to_local(const time_type& t)
200 {
201 time_duration_type td = dst_adjustor::utc_to_local_offset(t);
202 return t + td;
203 }
204 //! Convert a local time to utc
205 static time_type local_to_utc(const time_type& t,
206 date_time::dst_flags dst=date_time::calculate)
207 {
208 time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst);
209 return t + td;
210 }
211 };
212
213
214 } } //namespace date_time
215
216
217
218#endif
219

source code of boost/boost/date_time/local_time_adjustor.hpp