Commit | Line | Data |
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a272e669 MS |
1 | /* |
2 | ||
3 | Copyright (c) 2007-2008 Michael G Schwern | |
4 | ||
5 | This software originally derived from Paul Sheer's pivotal_gmtime_r.c. | |
6 | ||
7 | The MIT License: | |
8 | ||
9 | Permission is hereby granted, free of charge, to any person obtaining a copy | |
10 | of this software and associated documentation files (the "Software"), to deal | |
11 | in the Software without restriction, including without limitation the rights | |
12 | to use, copy, modify, merge, publish, distribute, sublicense, and/or sell | |
13 | copies of the Software, and to permit persons to whom the Software is | |
14 | furnished to do so, subject to the following conditions: | |
15 | ||
16 | The above copyright notice and this permission notice shall be included in | |
17 | all copies or substantial portions of the Software. | |
18 | ||
19 | THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR | |
20 | IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, | |
21 | FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE | |
22 | AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER | |
23 | LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, | |
24 | OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN | |
25 | THE SOFTWARE. | |
26 | ||
27 | */ | |
28 | ||
29 | /* | |
30 | ||
31 | Programmers who have available to them 64-bit time values as a 'long | |
32 | long' type can use localtime64_r() and gmtime64_r() which correctly | |
33 | converts the time even on 32-bit systems. Whether you have 64-bit time | |
34 | values will depend on the operating system. | |
35 | ||
36 | localtime64_r() is a 64-bit equivalent of localtime_r(). | |
37 | ||
38 | gmtime64_r() is a 64-bit equivalent of gmtime_r(). | |
39 | ||
40 | */ | |
41 | ||
7643e68f | 42 | #include "time64.h" |
af9b2bf5 | 43 | |
a272e669 MS |
44 | static const int days_in_month[2][12] = { |
45 | {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, | |
46 | {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, | |
47 | }; | |
48 | ||
49 | static const int julian_days_by_month[2][12] = { | |
50 | {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}, | |
51 | {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}, | |
52 | }; | |
53 | ||
54 | static const int length_of_year[2] = { 365, 366 }; | |
55 | ||
56 | /* Number of days in a 400 year Gregorian cycle */ | |
806a119a | 57 | static const Year years_in_gregorian_cycle = 400; |
a272e669 MS |
58 | static const int days_in_gregorian_cycle = (365 * 400) + 100 - 4 + 1; |
59 | ||
60 | /* 28 year calendar cycle between 2010 and 2037 */ | |
806a119a MS |
61 | #define SOLAR_CYCLE_LENGTH 28 |
62 | static const int safe_years[SOLAR_CYCLE_LENGTH] = { | |
a272e669 MS |
63 | 2016, 2017, 2018, 2019, |
64 | 2020, 2021, 2022, 2023, | |
65 | 2024, 2025, 2026, 2027, | |
66 | 2028, 2029, 2030, 2031, | |
67 | 2032, 2033, 2034, 2035, | |
68 | 2036, 2037, 2010, 2011, | |
69 | 2012, 2013, 2014, 2015 | |
70 | }; | |
71 | ||
ea722b76 | 72 | static const int dow_year_start[SOLAR_CYCLE_LENGTH] = { |
003c3b95 MS |
73 | 5, 0, 1, 2, /* 0 2016 - 2019 */ |
74 | 3, 5, 6, 0, /* 4 */ | |
75 | 1, 3, 4, 5, /* 8 */ | |
76 | 6, 1, 2, 3, /* 12 */ | |
77 | 4, 6, 0, 1, /* 16 */ | |
78 | 2, 4, 5, 6, /* 20 2036, 2037, 2010, 2011 */ | |
79 | 0, 2, 3, 4 /* 24 2012, 2013, 2014, 2015 */ | |
a272e669 MS |
80 | }; |
81 | ||
9af24521 MS |
82 | /* Let's assume people are going to be looking for dates in the future. |
83 | Let's provide some cheats so you can skip ahead. | |
84 | This has a 4x speed boost when near 2008. | |
85 | */ | |
86 | /* Number of days since epoch on Jan 1st, 2008 GMT */ | |
87 | #define CHEAT_DAYS (1199145600 / 24 / 60 / 60) | |
88 | #define CHEAT_YEARS 108 | |
a272e669 MS |
89 | |
90 | #define IS_LEAP(n) ((!(((n) + 1900) % 400) || (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0) | |
91 | #define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a)) | |
92 | ||
7bda3dfc MS |
93 | #define SHOULD_USE_SYSTEM_LOCALTIME(a) ( \ |
94 | USE_SYSTEM_LOCALTIME && \ | |
95 | (a) <= SYSTEM_LOCALTIME_MAX && \ | |
96 | (a) >= SYSTEM_LOCALTIME_MIN \ | |
97 | ) | |
98 | #define SHOULD_USE_SYSTEM_GMTIME(a) ( \ | |
99 | USE_SYSTEM_GMTIME && \ | |
100 | (a) <= SYSTEM_GMTIME_MAX && \ | |
101 | (a) >= SYSTEM_GMTIME_MIN \ | |
102 | ) | |
a64acb40 MS |
103 | |
104 | ||
806a119a | 105 | static int is_exception_century(Int64 year) |
a272e669 MS |
106 | { |
107 | int is_exception = ((year % 100 == 0) && !(year % 400 == 0)); | |
108 | /* printf("is_exception_century: %s\n", is_exception ? "yes" : "no"); */ | |
109 | ||
110 | return(is_exception); | |
111 | } | |
112 | ||
9af24521 | 113 | |
806a119a | 114 | Time64_T timegm64(struct TM *date) { |
ea722b76 MS |
115 | int days = 0; |
116 | Int64 seconds = 0; | |
117 | Int64 year; | |
a272e669 | 118 | |
9af24521 MS |
119 | if( date->tm_year > 70 ) { |
120 | year = 70; | |
121 | while( year < date->tm_year ) { | |
122 | days += length_of_year[IS_LEAP(year)]; | |
123 | year++; | |
a272e669 MS |
124 | } |
125 | } | |
9af24521 MS |
126 | else if ( date->tm_year < 70 ) { |
127 | year = 69; | |
128 | do { | |
129 | days -= length_of_year[IS_LEAP(year)]; | |
130 | year--; | |
131 | } while( year >= date->tm_year ); | |
132 | } | |
133 | ||
134 | days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon]; | |
135 | days += date->tm_mday - 1; | |
136 | ||
ea722b76 MS |
137 | /* Avoid overflowing the days integer */ |
138 | seconds = days; | |
139 | seconds = seconds * 60 * 60 * 24; | |
140 | ||
9af24521 MS |
141 | seconds += date->tm_hour * 60 * 60; |
142 | seconds += date->tm_min * 60; | |
143 | seconds += date->tm_sec; | |
144 | ||
ea722b76 | 145 | return((Time64_T)seconds); |
9af24521 MS |
146 | } |
147 | ||
148 | ||
806a119a | 149 | static int check_tm(struct TM *tm) |
9af24521 | 150 | { |
9af24521 | 151 | /* Don't forget leap seconds */ |
af9b2bf5 | 152 | assert(tm->tm_sec >= 0); |
9af24521 MS |
153 | assert(tm->tm_sec <= 61); |
154 | ||
af9b2bf5 | 155 | assert(tm->tm_min >= 0); |
9af24521 MS |
156 | assert(tm->tm_min <= 59); |
157 | ||
158 | assert(tm->tm_hour >= 0); | |
159 | assert(tm->tm_hour <= 23); | |
160 | ||
161 | assert(tm->tm_mday >= 1); | |
af9b2bf5 | 162 | assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]); |
9af24521 MS |
163 | |
164 | assert(tm->tm_mon >= 0); | |
165 | assert(tm->tm_mon <= 11); | |
166 | ||
167 | assert(tm->tm_wday >= 0); | |
168 | assert(tm->tm_wday <= 6); | |
169 | ||
170 | assert(tm->tm_yday >= 0); | |
af9b2bf5 | 171 | assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]); |
9af24521 MS |
172 | |
173 | #ifdef HAS_TM_TM_GMTOFF | |
174 | assert(tm->tm_gmtoff >= -24 * 60 * 60); | |
175 | assert(tm->tm_gmtoff <= 24 * 60 * 60); | |
176 | #endif | |
af9b2bf5 MS |
177 | |
178 | return 1; | |
a272e669 | 179 | } |
a64acb40 | 180 | |
a272e669 MS |
181 | |
182 | /* The exceptional centuries without leap years cause the cycle to | |
183 | shift by 16 | |
184 | */ | |
806a119a | 185 | static Year cycle_offset(Year year) |
a272e669 | 186 | { |
750c447b MS |
187 | const Year start_year = 2000; |
188 | Year year_diff = year - start_year; | |
189 | Year exceptions; | |
003c3b95 MS |
190 | |
191 | if( year > start_year ) | |
192 | year_diff--; | |
193 | ||
750c447b MS |
194 | exceptions = year_diff / 100; |
195 | exceptions -= year_diff / 400; | |
a272e669 | 196 | |
003c3b95 MS |
197 | /* |
198 | fprintf(stderr, "# year: %lld, exceptions: %lld, year_diff: %lld\n", | |
199 | year, exceptions, year_diff); | |
200 | */ | |
a272e669 MS |
201 | |
202 | return exceptions * 16; | |
203 | } | |
204 | ||
205 | /* For a given year after 2038, pick the latest possible matching | |
206 | year in the 28 year calendar cycle. | |
ea722b76 MS |
207 | |
208 | A matching year... | |
209 | 1) Starts on the same day of the week. | |
210 | 2) Has the same leap year status. | |
211 | ||
212 | This is so the calendars match up. | |
213 | ||
214 | Also the previous year must match. When doing Jan 1st you might | |
215 | wind up on Dec 31st the previous year when doing a -UTC time zone. | |
003c3b95 MS |
216 | |
217 | Finally, the next year must have the same start day of week. This | |
218 | is for Dec 31st with a +UTC time zone. | |
219 | It doesn't need the same leap year status since we only care about | |
220 | January 1st. | |
a272e669 | 221 | */ |
806a119a | 222 | static int safe_year(Year year) |
a272e669 MS |
223 | { |
224 | int safe_year; | |
806a119a | 225 | Year year_cycle = year + cycle_offset(year); |
a272e669 MS |
226 | |
227 | /* Change non-leap xx00 years to an equivalent */ | |
806a119a | 228 | if( is_exception_century(year) ) |
a272e669 MS |
229 | year_cycle += 11; |
230 | ||
003c3b95 | 231 | /* Also xx01 years, since the previous year will be wrong */ |
806a119a | 232 | if( is_exception_century(year - 1) ) |
003c3b95 MS |
233 | year_cycle += 17; |
234 | ||
a272e669 | 235 | year_cycle %= SOLAR_CYCLE_LENGTH; |
ea722b76 MS |
236 | if( year_cycle < 0 ) |
237 | year_cycle = SOLAR_CYCLE_LENGTH + year_cycle; | |
a272e669 | 238 | |
003c3b95 MS |
239 | assert( year_cycle >= 0 ); |
240 | assert( year_cycle < SOLAR_CYCLE_LENGTH ); | |
a272e669 MS |
241 | safe_year = safe_years[year_cycle]; |
242 | ||
243 | assert(safe_year <= 2037 && safe_year >= 2010); | |
244 | ||
245 | /* | |
246 | printf("year: %d, year_cycle: %d, safe_year: %d\n", | |
247 | year, year_cycle, safe_year); | |
248 | */ | |
249 | ||
250 | return safe_year; | |
251 | } | |
252 | ||
750c447b | 253 | |
806a119a MS |
254 | void copy_tm_to_TM(const struct tm *src, struct TM *dest) { |
255 | if( src == NULL ) { | |
256 | memset(dest, 0, sizeof(*dest)); | |
257 | } | |
258 | else { | |
259 | # ifdef USE_TM64 | |
260 | dest->tm_sec = src->tm_sec; | |
261 | dest->tm_min = src->tm_min; | |
262 | dest->tm_hour = src->tm_hour; | |
263 | dest->tm_mday = src->tm_mday; | |
264 | dest->tm_mon = src->tm_mon; | |
265 | dest->tm_year = (Year)src->tm_year; | |
266 | dest->tm_wday = src->tm_wday; | |
267 | dest->tm_yday = src->tm_yday; | |
268 | dest->tm_isdst = src->tm_isdst; | |
269 | ||
270 | # ifdef HAS_TM_TM_GMTOFF | |
271 | dest->tm_gmtoff = src->tm_gmtoff; | |
272 | # endif | |
273 | ||
274 | # ifdef HAS_TM_TM_ZONE | |
275 | dest->tm_zone = src->tm_zone; | |
276 | # endif | |
277 | ||
278 | # else | |
279 | /* They're the same type */ | |
280 | memcpy(dest, src, sizeof(*dest)); | |
281 | # endif | |
282 | } | |
283 | } | |
284 | ||
285 | ||
286 | void copy_TM_to_tm(const struct TM *src, struct tm *dest) { | |
287 | if( src == NULL ) { | |
288 | memset(dest, 0, sizeof(*dest)); | |
289 | } | |
290 | else { | |
291 | # ifdef USE_TM64 | |
292 | dest->tm_sec = src->tm_sec; | |
293 | dest->tm_min = src->tm_min; | |
294 | dest->tm_hour = src->tm_hour; | |
295 | dest->tm_mday = src->tm_mday; | |
296 | dest->tm_mon = src->tm_mon; | |
297 | dest->tm_year = (int)src->tm_year; | |
298 | dest->tm_wday = src->tm_wday; | |
299 | dest->tm_yday = src->tm_yday; | |
300 | dest->tm_isdst = src->tm_isdst; | |
301 | ||
302 | # ifdef HAS_TM_TM_GMTOFF | |
303 | dest->tm_gmtoff = src->tm_gmtoff; | |
304 | # endif | |
305 | ||
306 | # ifdef HAS_TM_TM_ZONE | |
307 | dest->tm_zone = src->tm_zone; | |
308 | # endif | |
309 | ||
310 | # else | |
311 | /* They're the same type */ | |
312 | memcpy(dest, src, sizeof(*dest)); | |
313 | # endif | |
314 | } | |
315 | } | |
316 | ||
317 | ||
948ea7a9 MS |
318 | /* Simulate localtime_r() to the best of our ability */ |
319 | struct tm * fake_localtime_r(const time_t *clock, struct tm *result) { | |
320 | const struct tm *static_result = localtime(clock); | |
321 | ||
322 | assert(result != NULL); | |
323 | ||
324 | if( static_result == NULL ) { | |
325 | memset(result, 0, sizeof(*result)); | |
326 | return NULL; | |
327 | } | |
328 | else { | |
329 | memcpy(result, static_result, sizeof(*result)); | |
330 | return result; | |
331 | } | |
332 | } | |
333 | ||
334 | ||
335 | /* Simulate gmtime_r() to the best of our ability */ | |
336 | struct tm * fake_gmtime_r(const time_t *clock, struct tm *result) { | |
337 | const struct tm *static_result = gmtime(clock); | |
338 | ||
339 | assert(result != NULL); | |
340 | ||
341 | if( static_result == NULL ) { | |
342 | memset(result, 0, sizeof(*result)); | |
343 | return NULL; | |
344 | } | |
345 | else { | |
346 | memcpy(result, static_result, sizeof(*result)); | |
347 | return result; | |
348 | } | |
349 | } | |
350 | ||
351 | ||
806a119a | 352 | struct TM *gmtime64_r (const Time64_T *in_time, struct TM *p) |
a272e669 MS |
353 | { |
354 | int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday; | |
9af24521 | 355 | Int64 v_tm_tday; |
a272e669 | 356 | int leap; |
9af24521 | 357 | Int64 m; |
a272e669 | 358 | Time64_T time = *in_time; |
750c447b | 359 | Year year = 70; |
806a119a | 360 | int cycles = 0; |
a272e669 | 361 | |
948ea7a9 MS |
362 | assert(p != NULL); |
363 | ||
a64acb40 MS |
364 | /* Use the system gmtime() if time_t is small enough */ |
365 | if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) { | |
366 | time_t safe_time = *in_time; | |
806a119a MS |
367 | struct tm safe_date; |
368 | GMTIME_R(&safe_time, &safe_date); | |
369 | ||
370 | copy_tm_to_TM(&safe_date, p); | |
371 | assert(check_tm(p)); | |
372 | ||
a64acb40 MS |
373 | return p; |
374 | } | |
375 | ||
9af24521 | 376 | #ifdef HAS_TM_TM_GMTOFF |
a272e669 MS |
377 | p->tm_gmtoff = 0; |
378 | #endif | |
379 | p->tm_isdst = 0; | |
380 | ||
9af24521 | 381 | #ifdef HAS_TM_TM_ZONE |
a272e669 MS |
382 | p->tm_zone = "UTC"; |
383 | #endif | |
384 | ||
750c447b | 385 | v_tm_sec = (int)(time % 60); |
a272e669 | 386 | time /= 60; |
750c447b | 387 | v_tm_min = (int)(time % 60); |
a272e669 | 388 | time /= 60; |
750c447b | 389 | v_tm_hour = (int)(time % 24); |
a272e669 MS |
390 | time /= 24; |
391 | v_tm_tday = time; | |
750c447b | 392 | |
a272e669 MS |
393 | WRAP (v_tm_sec, v_tm_min, 60); |
394 | WRAP (v_tm_min, v_tm_hour, 60); | |
395 | WRAP (v_tm_hour, v_tm_tday, 24); | |
750c447b MS |
396 | |
397 | v_tm_wday = (int)((v_tm_tday + 4) % 7); | |
398 | if (v_tm_wday < 0) | |
a272e669 MS |
399 | v_tm_wday += 7; |
400 | m = v_tm_tday; | |
a272e669 | 401 | |
9af24521 MS |
402 | if (m >= CHEAT_DAYS) { |
403 | year = CHEAT_YEARS; | |
404 | m -= CHEAT_DAYS; | |
405 | } | |
406 | ||
407 | if (m >= 0) { | |
a272e669 | 408 | /* Gregorian cycles, this is huge optimization for distant times */ |
806a119a MS |
409 | cycles = floor(m / (Time64_T) days_in_gregorian_cycle); |
410 | if( cycles ) { | |
411 | m -= (cycles * (Time64_T) days_in_gregorian_cycle); | |
412 | year += (cycles * years_in_gregorian_cycle); | |
a272e669 MS |
413 | } |
414 | ||
415 | /* Years */ | |
416 | leap = IS_LEAP (year); | |
417 | while (m >= (Time64_T) length_of_year[leap]) { | |
418 | m -= (Time64_T) length_of_year[leap]; | |
419 | year++; | |
420 | leap = IS_LEAP (year); | |
421 | } | |
422 | ||
423 | /* Months */ | |
424 | v_tm_mon = 0; | |
425 | while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) { | |
426 | m -= (Time64_T) days_in_month[leap][v_tm_mon]; | |
427 | v_tm_mon++; | |
428 | } | |
429 | } else { | |
9af24521 | 430 | year--; |
a272e669 MS |
431 | |
432 | /* Gregorian cycles */ | |
806a119a MS |
433 | cycles = ceil(m / (Time64_T) days_in_gregorian_cycle) + 1; |
434 | if( cycles ) { | |
435 | m -= (cycles * (Time64_T) days_in_gregorian_cycle); | |
436 | year += (cycles * years_in_gregorian_cycle); | |
a272e669 MS |
437 | } |
438 | ||
439 | /* Years */ | |
440 | leap = IS_LEAP (year); | |
441 | while (m < (Time64_T) -length_of_year[leap]) { | |
442 | m += (Time64_T) length_of_year[leap]; | |
443 | year--; | |
444 | leap = IS_LEAP (year); | |
445 | } | |
446 | ||
447 | /* Months */ | |
448 | v_tm_mon = 11; | |
449 | while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) { | |
450 | m += (Time64_T) days_in_month[leap][v_tm_mon]; | |
451 | v_tm_mon--; | |
452 | } | |
453 | m += (Time64_T) days_in_month[leap][v_tm_mon]; | |
454 | } | |
455 | ||
456 | p->tm_year = year; | |
457 | if( p->tm_year != year ) { | |
9af24521 | 458 | #ifdef EOVERFLOW |
a272e669 | 459 | errno = EOVERFLOW; |
9af24521 | 460 | #endif |
a272e669 MS |
461 | return NULL; |
462 | } | |
463 | ||
464 | p->tm_mday = (int) m + 1; | |
750c447b | 465 | p->tm_yday = (int) julian_days_by_month[leap][v_tm_mon] + m; |
a272e669 MS |
466 | p->tm_sec = v_tm_sec, p->tm_min = v_tm_min, p->tm_hour = v_tm_hour, |
467 | p->tm_mon = v_tm_mon, p->tm_wday = v_tm_wday; | |
468 | ||
806a119a | 469 | assert(check_tm(p)); |
a272e669 MS |
470 | |
471 | return p; | |
472 | } | |
473 | ||
474 | ||
806a119a | 475 | struct TM *localtime64_r (const Time64_T *time, struct TM *local_tm) |
a272e669 MS |
476 | { |
477 | time_t safe_time; | |
806a119a MS |
478 | struct tm safe_date; |
479 | struct TM gm_tm; | |
750c447b | 480 | Year orig_year; |
a272e669 MS |
481 | int month_diff; |
482 | ||
948ea7a9 MS |
483 | assert(local_tm != NULL); |
484 | ||
a64acb40 MS |
485 | /* Use the system localtime() if time_t is small enough */ |
486 | if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) { | |
487 | safe_time = *time; | |
806a119a MS |
488 | |
489 | LOCALTIME_R(&safe_time, &safe_date); | |
490 | ||
491 | copy_tm_to_TM(&safe_date, local_tm); | |
492 | assert(check_tm(local_tm)); | |
493 | ||
a64acb40 MS |
494 | return local_tm; |
495 | } | |
496 | ||
af832814 MS |
497 | if( gmtime64_r(time, &gm_tm) == NULL ) |
498 | return NULL; | |
499 | ||
a272e669 MS |
500 | orig_year = gm_tm.tm_year; |
501 | ||
c07fe26c MS |
502 | if (gm_tm.tm_year > (2037 - 1900) || |
503 | gm_tm.tm_year < (1902 - 1900) | |
504 | ) | |
505 | { | |
806a119a | 506 | gm_tm.tm_year = safe_year(gm_tm.tm_year + 1900) - 1900; |
c07fe26c | 507 | } |
a272e669 | 508 | |
806a119a MS |
509 | safe_time = timegm64(&gm_tm); |
510 | if( LOCALTIME_R(&safe_time, &safe_date) == NULL ) | |
af832814 | 511 | return NULL; |
a272e669 | 512 | |
806a119a MS |
513 | copy_tm_to_TM(&safe_date, local_tm); |
514 | ||
a272e669 | 515 | local_tm->tm_year = orig_year; |
af832814 MS |
516 | if( local_tm->tm_year != orig_year ) { |
517 | #ifdef EOVERFLOW | |
518 | errno = EOVERFLOW; | |
519 | #endif | |
520 | return NULL; | |
521 | } | |
522 | ||
523 | ||
a272e669 MS |
524 | month_diff = local_tm->tm_mon - gm_tm.tm_mon; |
525 | ||
526 | /* When localtime is Dec 31st previous year and | |
527 | gmtime is Jan 1st next year. | |
528 | */ | |
529 | if( month_diff == 11 ) { | |
530 | local_tm->tm_year--; | |
531 | } | |
532 | ||
533 | /* When localtime is Jan 1st, next year and | |
534 | gmtime is Dec 31st, previous year. | |
535 | */ | |
536 | if( month_diff == -11 ) { | |
537 | local_tm->tm_year++; | |
538 | } | |
539 | ||
540 | /* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st | |
541 | in a non-leap xx00. There is one point in the cycle | |
542 | we can't account for which the safe xx00 year is a leap | |
543 | year. So we need to correct for Dec 31st comming out as | |
544 | the 366th day of the year. | |
545 | */ | |
546 | if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 ) | |
547 | local_tm->tm_yday--; | |
548 | ||
806a119a | 549 | assert(check_tm(local_tm)); |
a272e669 MS |
550 | |
551 | return local_tm; | |
552 | } |