source: NonGTP/Boost/boost/date_time/local_time_adjustor.hpp @ 857

Revision 857, 8.2 KB checked in by igarcia, 19 years ago (diff)
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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 or http://www.boost.org/LICENSE-1.0)
8 * Author: Jeff Garland
9 * $Date: 2003/11/23 03:29:56 $
10 */
11
12/*! @file local_time_adjustor.hpp
13  Time adjustment calculations for local times
14*/
15
16#include "boost/date_time/date_generators.hpp"
17#include "boost/date_time/dst_rules.hpp"
18#include <stdexcept>
19
20namespace boost {
21  namespace date_time {
22
23
24    //! Provides a base offset adjustment from utc
25    template<class time_duration_type,
26             short hours, unsigned short minutes = 0>
27    class utc_adjustment
28    {
29    public:
30      static time_duration_type local_to_utc_base_offset()
31      {
32        time_duration_type td(hours,minutes,0);
33        return td.invert_sign();
34      }
35      static time_duration_type utc_to_local_base_offset()
36      {
37        return time_duration_type(hours,minutes,0);
38      }
39    };
40
41
42
43    //! Allow sliding utc adjustment with fixed dst rules
44    template<class time_type, class dst_rules>
45    class dynamic_local_time_adjustor : public dst_rules
46    {
47    public:
48      typedef typename time_type::time_duration_type time_duration_type;
49      typedef typename time_type::date_type date_type;
50
51      dynamic_local_time_adjustor(time_duration_type utc_offset) :
52        utc_offset_(utc_offset)
53      {}
54     
55      //! Presumes local time
56      time_duration_type utc_offset(bool is_dst)
57      {
58        if (is_dst) {
59          return utc_offset_ + this->dst_offset();
60        }
61        else {
62          return utc_offset_;
63        }
64
65      }
66    private:
67      time_duration_type utc_offset_;
68
69    };
70
71
72
73    //! Embed the rules for local time adjustments at compile time
74    template<class time_type, class dst_rules, class utc_offset_rules>
75    class static_local_time_adjustor: public dst_rules, public utc_offset_rules
76    {
77    public:
78      typedef typename time_type::time_duration_type time_duration_type;
79      typedef typename time_type::date_type date_type;
80
81      //! Calculates the offset from a utc time to local based on dst and utc offset
82      /*! @param t UTC time to calculate offset to local time
83       *  This adjustment depends on the following observations about the
84       *  workings of the DST boundary offset.  Since UTC time labels are
85       *  monotonically increasing we can determine if a given local time
86       *  is in DST or not and therefore adjust the offset appropriately.
87       *
88       *  The logic is as follows.  Starting with UTC time use the offset to
89       *  create a label for an non-dst adjusted local time.  Then call
90       *  dst_rules::local_is_dst with the non adjust local time.  The
91       *  results of this function will either unabiguously decide that
92       *  the initial local time is in dst or return an illegal or
93       *  ambiguous result.  An illegal result only occurs at the end
94       *  of dst (where labels are skipped) and indicates that dst has
95       *  ended.  An ambiguous result means that we need to recheck by
96       *  making a dst adjustment and then rechecking.  If the dst offset
97       *  is added to the utc time and the recheck proves non-ambiguous
98       *  then we are past the boundary.  If it is still ambiguous then
99       *  we are ahead of the boundary and dst is still in effect.
100       *
101       *  TODO -- check if all dst offsets are positive.  If not then
102       *  the algorithm needs to check for this and reverse the
103       *  illegal/ambiguous logic.
104       */
105      static time_duration_type utc_to_local_offset(const time_type& t)
106      {
107        //get initial local time guess by applying utc offset
108        time_type initial = t + utc_offset_rules::utc_to_local_base_offset();
109        time_is_dst_result dst_flag =
110          dst_rules::local_is_dst(initial.date(), initial.time_of_day());
111        switch(dst_flag) {
112    case is_in_dst:        return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
113        case is_not_in_dst:    return utc_offset_rules::utc_to_local_base_offset();
114        case invalid_time_label:return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
115        case ambiguous: {
116          time_type retry = initial + dst_rules::dst_offset();
117          dst_flag = dst_rules::local_is_dst(retry.date(), retry.time_of_day());
118          //if still ambibuous then the utc time still translates to a dst time
119          if (dst_flag == ambiguous) {
120            return utc_offset_rules::utc_to_local_base_offset() + dst_rules::dst_offset();
121          }
122          // we are past the dst boundary
123          else {
124            return utc_offset_rules::utc_to_local_base_offset();
125          }
126        }
127        }//case
128        //TODO  better excpetion type
129        throw std::out_of_range("Unreachable case");
130
131      }
132
133      //! Get the offset to UTC given a local time
134      static time_duration_type local_to_utc_offset(const time_type& t,
135                                                    date_time::dst_flags dst=date_time::calculate)
136      {
137        switch (dst) {
138        case is_dst:
139          return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
140        case not_dst:
141          return utc_offset_rules::local_to_utc_base_offset();
142        case calculate:
143          time_is_dst_result res =
144            dst_rules::local_is_dst(t.date(), t.time_of_day());
145          switch(res) {
146          case is_in_dst:      return utc_offset_rules::local_to_utc_base_offset() - dst_rules::dst_offset();
147          case is_not_in_dst:      return utc_offset_rules::local_to_utc_base_offset();
148          case ambiguous:          return utc_offset_rules::local_to_utc_base_offset();
149          case invalid_time_label: throw std::out_of_range("Time label invalid");
150          }
151        } 
152        throw std::out_of_range("Time label invalid");
153      }
154
155   
156    private:
157
158    };
159
160    void dummy_to_prevent_msvc6_ice(); //why ask why?
161
162    //! Template that simplifies the creation of local time calculator
163    /*! Use this template to create the timezone to utc convertors as required.
164     *
165     *  This class will also work for other regions that don't use dst and
166     *  have a utc offset which is an integral number of hours.
167     *
168     *  <b>Template Parameters</b>
169     *  -time_type  -- Time class to use
170     *  -utc_offset -- Number hours local time is adjust from utc
171     *  -use_dst -- true (default) if region uses dst, false otherwise
172     *  For example:
173     *  @code
174     *  //eastern timezone is utc-5
175     typedef date_time::local_adjustor<ptime, -5, us_dst> us_eastern;
176     typedef date_time::local_adjustor<ptime, -6, us_dst> us_central;
177     typedef date_time::local_adjustor<ptime, -7, us_dst> us_mountain;
178     typedef date_time::local_adjustor<ptime, -8, us_dst> us_pacific;
179     typedef date_time::local_adjustor<ptime, -7, no_dst> us_arizona;
180     @endcode
181     
182    */
183    template<class time_type, short utc_offset, class dst_rule>
184    class local_adjustor
185    {
186    public:
187      typedef typename time_type::time_duration_type time_duration_type;
188      typedef typename time_type::date_type date_type;
189      typedef static_local_time_adjustor<time_type,
190                                         dst_rule,
191                                         utc_adjustment<time_duration_type,
192                                                        utc_offset> > dst_adjustor;
193      //! Convert a utc time to local time
194      static time_type utc_to_local(const time_type& t)
195      {
196        time_duration_type td = dst_adjustor::utc_to_local_offset(t);
197        return t + td;
198      }
199      //! Convert a local time to utc
200      static time_type local_to_utc(const time_type& t,
201                                    date_time::dst_flags dst=date_time::calculate)
202      {
203        time_duration_type td = dst_adjustor::local_to_utc_offset(t, dst);
204        return t + td;
205      }
206    };
207
208
209  } } //namespace date_time
210
211
212
213#endif
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