| 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 | Perl_localtime64_r() is a 64-bit equivalent of localtime_r(). |
| 37 | |
| 38 | Perl_gmtime64_r() is a 64-bit equivalent of gmtime_r(). |
| 39 | |
| 40 | */ |
| 41 | |
| 42 | #include "EXTERN.h" |
| 43 | #define PERL_IN_TIME64_C |
| 44 | #include "perl.h" |
| 45 | #include "time64.h" |
| 46 | |
| 47 | static const char days_in_month[2][12] = { |
| 48 | {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, |
| 49 | {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}, |
| 50 | }; |
| 51 | |
| 52 | static const short julian_days_by_month[2][12] = { |
| 53 | {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334}, |
| 54 | {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335}, |
| 55 | }; |
| 56 | |
| 57 | static const short length_of_year[2] = { 365, 366 }; |
| 58 | |
| 59 | /* Number of days in a 400 year Gregorian cycle */ |
| 60 | static const Year years_in_gregorian_cycle = 400; |
| 61 | static const int days_in_gregorian_cycle = (365 * 400) + 100 - 4 + 1; |
| 62 | |
| 63 | /* 28 year calendar cycle between 2010 and 2037 */ |
| 64 | #define SOLAR_CYCLE_LENGTH 28 |
| 65 | static const short safe_years[SOLAR_CYCLE_LENGTH] = { |
| 66 | 2016, 2017, 2018, 2019, |
| 67 | 2020, 2021, 2022, 2023, |
| 68 | 2024, 2025, 2026, 2027, |
| 69 | 2028, 2029, 2030, 2031, |
| 70 | 2032, 2033, 2034, 2035, |
| 71 | 2036, 2037, 2010, 2011, |
| 72 | 2012, 2013, 2014, 2015 |
| 73 | }; |
| 74 | |
| 75 | /* Let's assume people are going to be looking for dates in the future. |
| 76 | Let's provide some cheats so you can skip ahead. |
| 77 | This has a 4x speed boost when near 2008. |
| 78 | */ |
| 79 | /* Number of days since epoch on Jan 1st, 2008 GMT */ |
| 80 | #define CHEAT_DAYS (1199145600 / 24 / 60 / 60) |
| 81 | #define CHEAT_YEARS 108 |
| 82 | |
| 83 | #define IS_LEAP(n) ((!(((n) + 1900) % 400) || (!(((n) + 1900) % 4) && (((n) + 1900) % 100))) != 0) |
| 84 | #undef WRAP /* some <termios.h> define this */ |
| 85 | #define WRAP(a,b,m) ((a) = ((a) < 0 ) ? ((b)--, (a) + (m)) : (a)) |
| 86 | |
| 87 | #ifdef USE_SYSTEM_LOCALTIME |
| 88 | # define SHOULD_USE_SYSTEM_LOCALTIME(a) ( \ |
| 89 | (a) <= SYSTEM_LOCALTIME_MAX && \ |
| 90 | (a) >= SYSTEM_LOCALTIME_MIN \ |
| 91 | ) |
| 92 | #else |
| 93 | # define SHOULD_USE_SYSTEM_LOCALTIME(a) (0) |
| 94 | #endif |
| 95 | |
| 96 | #ifdef USE_SYSTEM_GMTIME |
| 97 | # define SHOULD_USE_SYSTEM_GMTIME(a) ( \ |
| 98 | (a) <= SYSTEM_GMTIME_MAX && \ |
| 99 | (a) >= SYSTEM_GMTIME_MIN \ |
| 100 | ) |
| 101 | #else |
| 102 | # define SHOULD_USE_SYSTEM_GMTIME(a) (0) |
| 103 | #endif |
| 104 | |
| 105 | /* Multi varadic macros are a C99 thing, alas */ |
| 106 | #ifdef TIME_64_DEBUG |
| 107 | # define TIME64_TRACE(format) (fprintf(stderr, format)) |
| 108 | # define TIME64_TRACE1(format, var1) (fprintf(stderr, format, var1)) |
| 109 | # define TIME64_TRACE2(format, var1, var2) (fprintf(stderr, format, var1, var2)) |
| 110 | # define TIME64_TRACE3(format, var1, var2, var3) (fprintf(stderr, format, var1, var2, var3)) |
| 111 | #else |
| 112 | # define TIME64_TRACE(format) ((void)0) |
| 113 | # define TIME64_TRACE1(format, var1) ((void)0) |
| 114 | # define TIME64_TRACE2(format, var1, var2) ((void)0) |
| 115 | # define TIME64_TRACE3(format, var1, var2, var3) ((void)0) |
| 116 | #endif |
| 117 | |
| 118 | static int S_is_exception_century(Year year) |
| 119 | { |
| 120 | const int is_exception = ((year % 100 == 0) && !(year % 400 == 0)); |
| 121 | TIME64_TRACE1("# is_exception_century: %s\n", is_exception ? "yes" : "no"); |
| 122 | |
| 123 | return(is_exception); |
| 124 | } |
| 125 | |
| 126 | |
| 127 | static Time64_T S_timegm64(const struct TM *date) { |
| 128 | int days = 0; |
| 129 | Time64_T seconds = 0; |
| 130 | |
| 131 | if( date->tm_year > 70 ) { |
| 132 | Year year = 70; |
| 133 | while( year < date->tm_year ) { |
| 134 | days += length_of_year[IS_LEAP(year)]; |
| 135 | year++; |
| 136 | } |
| 137 | } |
| 138 | else if ( date->tm_year < 70 ) { |
| 139 | Year year = 69; |
| 140 | do { |
| 141 | days -= length_of_year[IS_LEAP(year)]; |
| 142 | year--; |
| 143 | } while( year >= date->tm_year ); |
| 144 | } |
| 145 | |
| 146 | days += julian_days_by_month[IS_LEAP(date->tm_year)][date->tm_mon]; |
| 147 | days += date->tm_mday - 1; |
| 148 | |
| 149 | /* Avoid overflowing the days integer */ |
| 150 | seconds = days; |
| 151 | seconds = seconds * 60 * 60 * 24; |
| 152 | |
| 153 | seconds += date->tm_hour * 60 * 60; |
| 154 | seconds += date->tm_min * 60; |
| 155 | seconds += date->tm_sec; |
| 156 | |
| 157 | return(seconds); |
| 158 | } |
| 159 | |
| 160 | |
| 161 | #ifdef DEBUGGING |
| 162 | static int S_check_tm(const struct TM *tm) |
| 163 | { |
| 164 | /* Don't forget leap seconds */ |
| 165 | assert(tm->tm_sec >= 0); |
| 166 | assert(tm->tm_sec <= 61); |
| 167 | |
| 168 | assert(tm->tm_min >= 0); |
| 169 | assert(tm->tm_min <= 59); |
| 170 | |
| 171 | assert(tm->tm_hour >= 0); |
| 172 | assert(tm->tm_hour <= 23); |
| 173 | |
| 174 | assert(tm->tm_mday >= 1); |
| 175 | assert(tm->tm_mday <= days_in_month[IS_LEAP(tm->tm_year)][tm->tm_mon]); |
| 176 | |
| 177 | assert(tm->tm_mon >= 0); |
| 178 | assert(tm->tm_mon <= 11); |
| 179 | |
| 180 | assert(tm->tm_wday >= 0); |
| 181 | assert(tm->tm_wday <= 6); |
| 182 | |
| 183 | assert(tm->tm_yday >= 0); |
| 184 | assert(tm->tm_yday <= length_of_year[IS_LEAP(tm->tm_year)]); |
| 185 | |
| 186 | #ifdef HAS_TM_TM_GMTOFF |
| 187 | assert(tm->tm_gmtoff >= -24 * 60 * 60); |
| 188 | assert(tm->tm_gmtoff <= 24 * 60 * 60); |
| 189 | #endif |
| 190 | |
| 191 | return 1; |
| 192 | } |
| 193 | #endif |
| 194 | |
| 195 | |
| 196 | /* The exceptional centuries without leap years cause the cycle to |
| 197 | shift by 16 |
| 198 | */ |
| 199 | static Year S_cycle_offset(Year year) |
| 200 | { |
| 201 | const Year start_year = 2000; |
| 202 | Year year_diff = year - start_year; |
| 203 | Year exceptions; |
| 204 | |
| 205 | if( year > start_year ) |
| 206 | year_diff--; |
| 207 | |
| 208 | exceptions = year_diff / 100; |
| 209 | exceptions -= year_diff / 400; |
| 210 | |
| 211 | TIME64_TRACE3("# year: %lld, exceptions: %lld, year_diff: %lld\n", |
| 212 | year, exceptions, year_diff); |
| 213 | |
| 214 | return exceptions * 16; |
| 215 | } |
| 216 | |
| 217 | /* For a given year after 2038, pick the latest possible matching |
| 218 | year in the 28 year calendar cycle. |
| 219 | |
| 220 | A matching year... |
| 221 | 1) Starts on the same day of the week. |
| 222 | 2) Has the same leap year status. |
| 223 | |
| 224 | This is so the calendars match up. |
| 225 | |
| 226 | Also the previous year must match. When doing Jan 1st you might |
| 227 | wind up on Dec 31st the previous year when doing a -UTC time zone. |
| 228 | |
| 229 | Finally, the next year must have the same start day of week. This |
| 230 | is for Dec 31st with a +UTC time zone. |
| 231 | It doesn't need the same leap year status since we only care about |
| 232 | January 1st. |
| 233 | */ |
| 234 | static int S_safe_year(Year year) |
| 235 | { |
| 236 | int safe_year; |
| 237 | Year year_cycle = year + S_cycle_offset(year); |
| 238 | |
| 239 | /* Change non-leap xx00 years to an equivalent */ |
| 240 | if( S_is_exception_century(year) ) |
| 241 | year_cycle += 11; |
| 242 | |
| 243 | /* Also xx01 years, since the previous year will be wrong */ |
| 244 | if( S_is_exception_century(year - 1) ) |
| 245 | year_cycle += 17; |
| 246 | |
| 247 | year_cycle %= SOLAR_CYCLE_LENGTH; |
| 248 | if( year_cycle < 0 ) |
| 249 | year_cycle = SOLAR_CYCLE_LENGTH + year_cycle; |
| 250 | |
| 251 | assert( year_cycle >= 0 ); |
| 252 | assert( year_cycle < SOLAR_CYCLE_LENGTH ); |
| 253 | safe_year = safe_years[year_cycle]; |
| 254 | |
| 255 | assert(safe_year <= 2037 && safe_year >= 2010); |
| 256 | |
| 257 | TIME64_TRACE3("# year: %lld, year_cycle: %lld, safe_year: %d\n", |
| 258 | year, year_cycle, safe_year); |
| 259 | |
| 260 | return safe_year; |
| 261 | } |
| 262 | |
| 263 | |
| 264 | static void S_copy_little_tm_to_big_TM(const struct tm *src, struct TM *dest) { |
| 265 | assert(src); |
| 266 | assert(dest); |
| 267 | #ifdef USE_TM64 |
| 268 | dest->tm_sec = src->tm_sec; |
| 269 | dest->tm_min = src->tm_min; |
| 270 | dest->tm_hour = src->tm_hour; |
| 271 | dest->tm_mday = src->tm_mday; |
| 272 | dest->tm_mon = src->tm_mon; |
| 273 | dest->tm_year = (Year)src->tm_year; |
| 274 | dest->tm_wday = src->tm_wday; |
| 275 | dest->tm_yday = src->tm_yday; |
| 276 | dest->tm_isdst = src->tm_isdst; |
| 277 | |
| 278 | # ifdef HAS_TM_TM_GMTOFF |
| 279 | dest->tm_gmtoff = src->tm_gmtoff; |
| 280 | # endif |
| 281 | |
| 282 | # ifdef HAS_TM_TM_ZONE |
| 283 | dest->tm_zone = src->tm_zone; |
| 284 | # endif |
| 285 | |
| 286 | #else |
| 287 | /* They're the same type */ |
| 288 | memcpy(dest, src, sizeof(*dest)); |
| 289 | #endif |
| 290 | } |
| 291 | |
| 292 | |
| 293 | #ifndef HAS_LOCALTIME_R |
| 294 | /* Simulate localtime_r() to the best of our ability */ |
| 295 | static struct tm * S_localtime_r(const time_t *clock, struct tm *result) { |
| 296 | #ifdef __VMS |
| 297 | dTHX; /* the following is defined as Perl_my_localtime(aTHX_ ...) */ |
| 298 | #endif |
| 299 | const struct tm * const static_result = localtime(clock); |
| 300 | |
| 301 | assert(result != NULL); |
| 302 | |
| 303 | if( static_result == NULL ) { |
| 304 | memset(result, 0, sizeof(*result)); |
| 305 | return NULL; |
| 306 | } |
| 307 | else { |
| 308 | memcpy(result, static_result, sizeof(*result)); |
| 309 | return result; |
| 310 | } |
| 311 | } |
| 312 | #endif |
| 313 | |
| 314 | #ifndef HAS_GMTIME_R |
| 315 | /* Simulate gmtime_r() to the best of our ability */ |
| 316 | static struct tm * S_gmtime_r(const time_t *clock, struct tm *result) { |
| 317 | #ifdef __VMS |
| 318 | dTHX; /* the following is defined as Perl_my_localtime(aTHX_ ...) */ |
| 319 | #endif |
| 320 | const struct tm * const static_result = gmtime(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 | #endif |
| 334 | |
| 335 | struct TM *Perl_gmtime64_r (const Time64_T *in_time, struct TM *p) |
| 336 | { |
| 337 | int v_tm_sec, v_tm_min, v_tm_hour, v_tm_mon, v_tm_wday; |
| 338 | Time64_T v_tm_tday; |
| 339 | int leap; |
| 340 | Time64_T m; |
| 341 | Time64_T time = *in_time; |
| 342 | Year year = 70; |
| 343 | |
| 344 | assert(p != NULL); |
| 345 | |
| 346 | /* Use the system gmtime() if time_t is small enough */ |
| 347 | if( SHOULD_USE_SYSTEM_GMTIME(*in_time) ) { |
| 348 | time_t safe_time = (time_t)*in_time; |
| 349 | struct tm safe_date; |
| 350 | GMTIME_R(&safe_time, &safe_date); |
| 351 | |
| 352 | S_copy_little_tm_to_big_TM(&safe_date, p); |
| 353 | assert(S_check_tm(p)); |
| 354 | |
| 355 | return p; |
| 356 | } |
| 357 | |
| 358 | #ifdef HAS_TM_TM_GMTOFF |
| 359 | p->tm_gmtoff = 0; |
| 360 | #endif |
| 361 | p->tm_isdst = 0; |
| 362 | |
| 363 | #ifdef HAS_TM_TM_ZONE |
| 364 | p->tm_zone = (char *)"UTC"; |
| 365 | #endif |
| 366 | |
| 367 | v_tm_sec = (int)Perl_fmod(time, 60.0); |
| 368 | time = time >= 0 ? Perl_floor(time / 60.0) : Perl_ceil(time / 60.0); |
| 369 | v_tm_min = (int)Perl_fmod(time, 60.0); |
| 370 | time = time >= 0 ? Perl_floor(time / 60.0) : Perl_ceil(time / 60.0); |
| 371 | v_tm_hour = (int)Perl_fmod(time, 24.0); |
| 372 | time = time >= 0 ? Perl_floor(time / 24.0) : Perl_ceil(time / 24.0); |
| 373 | v_tm_tday = time; |
| 374 | |
| 375 | WRAP (v_tm_sec, v_tm_min, 60); |
| 376 | WRAP (v_tm_min, v_tm_hour, 60); |
| 377 | WRAP (v_tm_hour, v_tm_tday, 24); |
| 378 | |
| 379 | v_tm_wday = (int)Perl_fmod((v_tm_tday + 4.0), 7.0); |
| 380 | if (v_tm_wday < 0) |
| 381 | v_tm_wday += 7; |
| 382 | m = v_tm_tday; |
| 383 | |
| 384 | if (m >= CHEAT_DAYS) { |
| 385 | year = CHEAT_YEARS; |
| 386 | m -= CHEAT_DAYS; |
| 387 | } |
| 388 | |
| 389 | if (m >= 0) { |
| 390 | /* Gregorian cycles, this is huge optimization for distant times */ |
| 391 | const int cycles = (int)Perl_floor(m / (Time64_T) days_in_gregorian_cycle); |
| 392 | if( cycles ) { |
| 393 | m -= (cycles * (Time64_T) days_in_gregorian_cycle); |
| 394 | year += (cycles * years_in_gregorian_cycle); |
| 395 | } |
| 396 | |
| 397 | /* Years */ |
| 398 | leap = IS_LEAP (year); |
| 399 | while (m >= (Time64_T) length_of_year[leap]) { |
| 400 | m -= (Time64_T) length_of_year[leap]; |
| 401 | year++; |
| 402 | leap = IS_LEAP (year); |
| 403 | } |
| 404 | |
| 405 | /* Months */ |
| 406 | v_tm_mon = 0; |
| 407 | while (m >= (Time64_T) days_in_month[leap][v_tm_mon]) { |
| 408 | m -= (Time64_T) days_in_month[leap][v_tm_mon]; |
| 409 | v_tm_mon++; |
| 410 | } |
| 411 | } else { |
| 412 | int cycles; |
| 413 | |
| 414 | year--; |
| 415 | |
| 416 | /* Gregorian cycles */ |
| 417 | cycles = (int)Perl_ceil((m / (Time64_T) days_in_gregorian_cycle) + 1); |
| 418 | if( cycles ) { |
| 419 | m -= (cycles * (Time64_T) days_in_gregorian_cycle); |
| 420 | year += (cycles * years_in_gregorian_cycle); |
| 421 | } |
| 422 | |
| 423 | /* Years */ |
| 424 | leap = IS_LEAP (year); |
| 425 | while (m < (Time64_T) -length_of_year[leap]) { |
| 426 | m += (Time64_T) length_of_year[leap]; |
| 427 | year--; |
| 428 | leap = IS_LEAP (year); |
| 429 | } |
| 430 | |
| 431 | /* Months */ |
| 432 | v_tm_mon = 11; |
| 433 | while (m < (Time64_T) -days_in_month[leap][v_tm_mon]) { |
| 434 | m += (Time64_T) days_in_month[leap][v_tm_mon]; |
| 435 | v_tm_mon--; |
| 436 | } |
| 437 | m += (Time64_T) days_in_month[leap][v_tm_mon]; |
| 438 | } |
| 439 | |
| 440 | p->tm_year = year; |
| 441 | if( p->tm_year != year ) { |
| 442 | #ifdef EOVERFLOW |
| 443 | errno = EOVERFLOW; |
| 444 | #endif |
| 445 | return NULL; |
| 446 | } |
| 447 | |
| 448 | /* At this point m is less than a year so casting to an int is safe */ |
| 449 | p->tm_mday = (int) m + 1; |
| 450 | p->tm_yday = julian_days_by_month[leap][v_tm_mon] + (int)m; |
| 451 | p->tm_sec = v_tm_sec; |
| 452 | p->tm_min = v_tm_min; |
| 453 | p->tm_hour = v_tm_hour; |
| 454 | p->tm_mon = v_tm_mon; |
| 455 | p->tm_wday = v_tm_wday; |
| 456 | |
| 457 | assert(S_check_tm(p)); |
| 458 | |
| 459 | return p; |
| 460 | } |
| 461 | |
| 462 | |
| 463 | struct TM *Perl_localtime64_r (const Time64_T *time, struct TM *local_tm) |
| 464 | { |
| 465 | time_t safe_time; |
| 466 | struct tm safe_date; |
| 467 | struct TM gm_tm; |
| 468 | Year orig_year; |
| 469 | int month_diff; |
| 470 | |
| 471 | assert(local_tm != NULL); |
| 472 | |
| 473 | /* Use the system localtime() if time_t is small enough */ |
| 474 | if( SHOULD_USE_SYSTEM_LOCALTIME(*time) ) { |
| 475 | safe_time = (time_t)*time; |
| 476 | |
| 477 | TIME64_TRACE1("Using system localtime for %lld\n", *time); |
| 478 | |
| 479 | LOCALTIME_R(&safe_time, &safe_date); |
| 480 | |
| 481 | S_copy_little_tm_to_big_TM(&safe_date, local_tm); |
| 482 | assert(S_check_tm(local_tm)); |
| 483 | |
| 484 | return local_tm; |
| 485 | } |
| 486 | |
| 487 | if( Perl_gmtime64_r(time, &gm_tm) == NULL ) { |
| 488 | TIME64_TRACE1("gmtime64_r returned null for %lld\n", *time); |
| 489 | return NULL; |
| 490 | } |
| 491 | |
| 492 | orig_year = gm_tm.tm_year; |
| 493 | |
| 494 | if (gm_tm.tm_year > (2037 - 1900) || |
| 495 | gm_tm.tm_year < (1970 - 1900) |
| 496 | ) |
| 497 | { |
| 498 | TIME64_TRACE1("Mapping tm_year %lld to safe_year\n", (Year)gm_tm.tm_year); |
| 499 | gm_tm.tm_year = S_safe_year((Year)(gm_tm.tm_year + 1900)) - 1900; |
| 500 | } |
| 501 | |
| 502 | safe_time = (time_t)S_timegm64(&gm_tm); |
| 503 | if( LOCALTIME_R(&safe_time, &safe_date) == NULL ) { |
| 504 | TIME64_TRACE1("localtime_r(%d) returned NULL\n", (int)safe_time); |
| 505 | return NULL; |
| 506 | } |
| 507 | |
| 508 | S_copy_little_tm_to_big_TM(&safe_date, local_tm); |
| 509 | |
| 510 | local_tm->tm_year = orig_year; |
| 511 | if( local_tm->tm_year != orig_year ) { |
| 512 | TIME64_TRACE2("tm_year overflow: tm_year %lld, orig_year %lld\n", |
| 513 | (Year)local_tm->tm_year, (Year)orig_year); |
| 514 | |
| 515 | #ifdef EOVERFLOW |
| 516 | errno = EOVERFLOW; |
| 517 | #endif |
| 518 | return NULL; |
| 519 | } |
| 520 | |
| 521 | |
| 522 | month_diff = local_tm->tm_mon - gm_tm.tm_mon; |
| 523 | |
| 524 | /* When localtime is Dec 31st previous year and |
| 525 | gmtime is Jan 1st next year. |
| 526 | */ |
| 527 | if( month_diff == 11 ) { |
| 528 | local_tm->tm_year--; |
| 529 | } |
| 530 | |
| 531 | /* When localtime is Jan 1st, next year and |
| 532 | gmtime is Dec 31st, previous year. |
| 533 | */ |
| 534 | if( month_diff == -11 ) { |
| 535 | local_tm->tm_year++; |
| 536 | } |
| 537 | |
| 538 | /* GMT is Jan 1st, xx01 year, but localtime is still Dec 31st |
| 539 | in a non-leap xx00. There is one point in the cycle |
| 540 | we can't account for which the safe xx00 year is a leap |
| 541 | year. So we need to correct for Dec 31st coming out as |
| 542 | the 366th day of the year. |
| 543 | */ |
| 544 | if( !IS_LEAP(local_tm->tm_year) && local_tm->tm_yday == 365 ) |
| 545 | local_tm->tm_yday--; |
| 546 | |
| 547 | assert(S_check_tm(local_tm)); |
| 548 | |
| 549 | return local_tm; |
| 550 | } |