CFDate.c

   1 /*
   2  * Copyright (c) 2012 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 /*      CFDate.c
  25         Copyright (c) 1998-2011, Apple Inc. All rights reserved.
  26         Responsibility: Christopher Kane
  27 */
  28
  29 #include <CoreFoundation/CFDate.h>
  30 #include <CoreFoundation/CFTimeZone.h>
  31 #include <CoreFoundation/CFDictionary.h>
  32 #include <CoreFoundation/CFArray.h>
  33 #include <CoreFoundation/CFString.h>
  34 #include <CoreFoundation/CFNumber.h>
  35 #include "CFInternal.h"
  36 #include <math.h>
  37 #if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_LINUX
  38 #include <sys/time.h>
  39 #elif DEPLOYMENT_TARGET_WINDOWS
  40 #else
  41 #error Unknown or unspecified DEPLOYMENT_TARGET
  42 #endif
  43
  44
  45 /* cjk: The Julian Date for the reference date is 2451910.5,
  46         I think, in case that's ever useful. */
  47
  48 #define DEFINE_CFDATE_FUNCTIONS 1
  49
  50 #if DEFINE_CFDATE_FUNCTIONS
  51
  52 const CFTimeInterval kCFAbsoluteTimeIntervalSince1970 = 978307200.0L;
  53 const CFTimeInterval kCFAbsoluteTimeIntervalSince1904 = 3061152000.0L;
  54
  55 __private_extern__ double __CFTSRRate = 0.0;
  56 static double __CF1_TSRRate = 0.0;
  57
  58 __private_extern__ int64_t __CFTimeIntervalToTSR(CFTimeInterval ti) {
  59     if ((ti * __CFTSRRate) > INT64_MAX / 2) return (INT64_MAX / 2);
  60     return (int64_t)(ti * __CFTSRRate);
  61 }
  62
  63 __private_extern__ CFTimeInterval __CFTSRToTimeInterval(int64_t tsr) {
  64     return (CFTimeInterval)((double)tsr * __CF1_TSRRate);
  65 }
  66
  67 CFAbsoluteTime CFAbsoluteTimeGetCurrent(void) {
  68     CFAbsoluteTime ret;
  69 #if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED || DEPLOYMENT_TARGET_LINUX
  70     struct timeval tv;
  71     gettimeofday(&tv, NULL);
  72     ret = (CFTimeInterval)tv.tv_sec - kCFAbsoluteTimeIntervalSince1970;
  73     ret += (1.0E-6 * (CFTimeInterval)tv.tv_usec);
  74 #elif DEPLOYMENT_TARGET_WINDOWS
  75     FILETIME ft;
  76     GetSystemTimeAsFileTime(&ft);
  77     ret = _CFAbsoluteTimeFromFileTime(&ft);
  78 #else
  79 #error Unknown or unspecified DEPLOYMENT_TARGET
  80 #endif
  81     return ret;
  82 }
  83
  84 __private_extern__ void __CFDateInitialize(void) {
  85 #if DEPLOYMENT_TARGET_MACOSX || DEPLOYMENT_TARGET_EMBEDDED
  86     struct mach_timebase_info info;
  87     mach_timebase_info(&info);
  88     __CFTSRRate = (1.0E9 / (double)info.numer) * (double)info.denom;
  89     __CF1_TSRRate = 1.0 / __CFTSRRate;
  90 #elif DEPLOYMENT_TARGET_WINDOWS
  91     LARGE_INTEGER freq;
  92     if (!QueryPerformanceFrequency(&freq)) {
  93         HALT;
  94     }
  95     __CFTSRRate = (double)freq.QuadPart;
  96     __CF1_TSRRate = 1.0 / __CFTSRRate;
  97 #elif DEPLOYMENT_TARGET_LINUX
  98     struct timespec res;
  99     if (!clock_getres(CLOCK_MONOTONIC, &res)) {
 100         HALT;
 101     }
 102     __CFTSRRate = res.tv_sec + (1000000000 * res.tv_nsec);
 103     __CF1_TSRRate = 1.0 / __CFTSRRate;
 104 #else
 105 #error Unknown or unspecified DEPLOYMENT_TARGET
 106 #endif
 107     CFDateGetTypeID(); // cause side-effects
 108 }
 109
 110 #if 1
 111 struct __CFDate {
 112     CFRuntimeBase _base;
 113     CFAbsoluteTime _time;       /* immutable */
 114 };
 115
 116 static Boolean __CFDateEqual(CFTypeRef cf1, CFTypeRef cf2) {
 117     CFDateRef date1 = (CFDateRef)cf1;
 118     CFDateRef date2 = (CFDateRef)cf2;
 119     if (date1->_time != date2->_time) return false;
 120     return true;
 121 }
 122
 123 static CFHashCode __CFDateHash(CFTypeRef cf) {
 124     CFDateRef date = (CFDateRef)cf;
 125     return (CFHashCode)(float)floor(date->_time);
 126 }
 127
 128 static CFStringRef __CFDateCopyDescription(CFTypeRef cf) {
 129     CFDateRef date = (CFDateRef)cf;
 130     return CFStringCreateWithFormat(CFGetAllocator(date), NULL, CFSTR("<CFDate %p [%p]>{time = %0.09g}"), cf, CFGetAllocator(date), date->_time);
 131 }
 132
 133 static CFTypeID __kCFDateTypeID = _kCFRuntimeNotATypeID;
 134
 135 static const CFRuntimeClass __CFDateClass = {
 136     0,
 137     "CFDate",
 138     NULL,       // init
 139     NULL,       // copy
 140     NULL,       // dealloc
 141     __CFDateEqual,
 142     __CFDateHash,
 143     NULL,       //
 144     __CFDateCopyDescription
 145 };
 146
 147 CFTypeID CFDateGetTypeID(void) {
 148     if (_kCFRuntimeNotATypeID == __kCFDateTypeID) __kCFDateTypeID = _CFRuntimeRegisterClass(&__CFDateClass);
 149     return __kCFDateTypeID;
 150 }
 151
 152 CFDateRef CFDateCreate(CFAllocatorRef allocator, CFAbsoluteTime at) {
 153     CFDateRef memory;
 154     uint32_t size;
 155     size = sizeof(struct __CFDate) - sizeof(CFRuntimeBase);
 156     memory = (CFDateRef)_CFRuntimeCreateInstance(allocator, CFDateGetTypeID(), size, NULL);
 157     if (NULL == memory) {
 158         return NULL;
 159     }
 160     ((struct __CFDate *)memory)->_time = at;
 161     return memory;
 162 }
 163
 164 CFTimeInterval CFDateGetAbsoluteTime(CFDateRef date) {
 165     CF_OBJC_FUNCDISPATCH0(CFDateGetTypeID(), CFTimeInterval, date, "timeIntervalSinceReferenceDate");
 166     __CFGenericValidateType(date, CFDateGetTypeID());
 167     return date->_time;
 168 }
 169
 170 CFTimeInterval CFDateGetTimeIntervalSinceDate(CFDateRef date, CFDateRef otherDate) {
 171     CF_OBJC_FUNCDISPATCH1(CFDateGetTypeID(), CFTimeInterval, date, "timeIntervalSinceDate:", otherDate);
 172     __CFGenericValidateType(date, CFDateGetTypeID());
 173     __CFGenericValidateType(otherDate, CFDateGetTypeID());
 174     return date->_time - otherDate->_time;
 175 }
 176
 177 CFComparisonResult CFDateCompare(CFDateRef date, CFDateRef otherDate, void *context) {
 178     CF_OBJC_FUNCDISPATCH1(CFDateGetTypeID(), CFComparisonResult, date, "compare:", otherDate);
 179     __CFGenericValidateType(date, CFDateGetTypeID());
 180     __CFGenericValidateType(otherDate, CFDateGetTypeID());
 181     if (date->_time < otherDate->_time) return kCFCompareLessThan;
 182     if (date->_time > otherDate->_time) return kCFCompareGreaterThan;
 183     return kCFCompareEqualTo;
 184 }
 185 #endif
 186
 187 #endif
 188
 189 CF_INLINE int32_t __CFDoubleModToInt(double d, int32_t modulus) {
 190     int32_t result = (int32_t)(float)floor(d - floor(d / modulus) * modulus);
 191     if (result < 0) result += modulus;
 192     return result;
 193 }
 194
 195 CF_INLINE double __CFDoubleMod(double d, int32_t modulus) {
 196     double result = d - floor(d / modulus) * modulus;
 197     if (result < 0.0) result += (double)modulus;
 198     return result;
 199 }
 200
 201 static const uint8_t daysInMonth[16] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 0, 0, 0};
 202 static const uint16_t daysBeforeMonth[16] = {0, 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365, 0, 0};
 203 static const uint16_t daysAfterMonth[16] = {365, 334, 306, 275, 245, 214, 184, 153, 122, 92, 61, 31, 0, 0, 0, 0};
 204
 205 CF_INLINE bool isleap(int64_t year) {
 206     int64_t y = (year + 1) % 400;       /* correct to nearest multiple-of-400 year, then find the remainder */
 207     if (y < 0) y = -y;
 208     return (0 == (y & 3) && 100 != y && 200 != y && 300 != y);
 209 }
 210
 211 /* year arg is absolute year; Gregorian 2001 == year 0; 2001/1/1 = absolute date 0 */
 212 CF_INLINE uint8_t __CFDaysInMonth(int8_t month, int64_t year, bool leap) {
 213     return daysInMonth[month] + (2 == month && leap);
 214 }
 215
 216 /* year arg is absolute year; Gregorian 2001 == year 0; 2001/1/1 = absolute date 0 */
 217 CF_INLINE uint16_t __CFDaysBeforeMonth(int8_t month, int64_t year, bool leap) {
 218     return daysBeforeMonth[month] + (2 < month && leap);
 219 }
 220
 221 /* year arg is absolute year; Gregorian 2001 == year 0; 2001/1/1 = absolute date 0 */
 222 CF_INLINE uint16_t __CFDaysAfterMonth(int8_t month, int64_t year, bool leap) {
 223     return daysAfterMonth[month] + (month < 2 && leap);
 224 }
 225
 226 /* year arg is absolute year; Gregorian 2001 == year 0; 2001/1/1 = absolute date 0 */
 227 static void __CFYMDFromAbsolute(int64_t absolute, int64_t *year, int8_t *month, int8_t *day) {
 228     int64_t b = absolute / 146097; // take care of as many multiples of 400 years as possible
 229     int64_t y = b * 400;
 230     uint16_t ydays;
 231     absolute -= b * 146097;
 232     while (absolute < 0) {
 233         y -= 1;
 234         absolute += __CFDaysAfterMonth(0, y, isleap(y));
 235     }
 236     /* Now absolute is non-negative days to add to year */
 237     ydays = __CFDaysAfterMonth(0, y, isleap(y));
 238     while (ydays <= absolute) {
 239         y += 1;
 240         absolute -= ydays;
 241         ydays = __CFDaysAfterMonth(0, y, isleap(y));
 242     }
 243     /* Now we have year and days-into-year */
 244     if (year) *year = y;
 245     if (month || day) {
 246         int8_t m = absolute / 33 + 1; /* search from the approximation */
 247         bool leap = isleap(y);
 248         while (__CFDaysBeforeMonth(m + 1, y, leap) <= absolute) m++;
 249         if (month) *month = m;
 250         if (day) *day = absolute - __CFDaysBeforeMonth(m, y, leap) + 1;
 251     }
 252 }
 253
 254 /* year arg is absolute year; Gregorian 2001 == year 0; 2001/1/1 = absolute date 0 */
 255 static double __CFAbsoluteFromYMD(int64_t year, int8_t month, int8_t day) {
 256     double absolute = 0.0;
 257     int64_t idx;
 258     int64_t b = year / 400; // take care of as many multiples of 400 years as possible
 259     absolute += b * 146097.0;
 260     year -= b * 400;
 261     if (year < 0) {
 262         for (idx = year; idx < 0; idx++)
 263             absolute -= __CFDaysAfterMonth(0, idx, isleap(idx));
 264     } else {
 265         for (idx = 0; idx < year; idx++)
 266             absolute += __CFDaysAfterMonth(0, idx, isleap(idx));
 267     }
 268     /* Now add the days into the original year */
 269     absolute += __CFDaysBeforeMonth(month, year, isleap(year)) + day - 1;
 270     return absolute;
 271 }
 272
 273 Boolean CFGregorianDateIsValid(CFGregorianDate gdate, CFOptionFlags unitFlags) {
 274     if ((unitFlags & kCFGregorianUnitsYears) && (gdate.year <= 0)) return false;
 275     if ((unitFlags & kCFGregorianUnitsMonths) && (gdate.month < 1 || 12 < gdate.month)) return false;
 276     if ((unitFlags & kCFGregorianUnitsDays) && (gdate.day < 1 || 31 < gdate.day)) return false;
 277     if ((unitFlags & kCFGregorianUnitsHours) && (gdate.hour < 0 || 23 < gdate.hour)) return false;
 278     if ((unitFlags & kCFGregorianUnitsMinutes) && (gdate.minute < 0 || 59 < gdate.minute)) return false;
 279     if ((unitFlags & kCFGregorianUnitsSeconds) && (gdate.second < 0.0 || 60.0 <= gdate.second)) return false;
 280     if ((unitFlags & kCFGregorianUnitsDays) && (unitFlags & kCFGregorianUnitsMonths) && (unitFlags & kCFGregorianUnitsYears) && (__CFDaysInMonth(gdate.month, gdate.year - 2001, isleap(gdate.year - 2001)) < gdate.day)) return false;
 281     return true;
 282 }
 283
 284 CFAbsoluteTime CFGregorianDateGetAbsoluteTime(CFGregorianDate gdate, CFTimeZoneRef tz) {
 285     CFAbsoluteTime at;
 286     CFTimeInterval offset0, offset1;
 287     if (NULL != tz) {
 288         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 289     }
 290     at = 86400.0 * __CFAbsoluteFromYMD(gdate.year - 2001, gdate.month, gdate.day);
 291     at += 3600.0 * gdate.hour + 60.0 * gdate.minute + gdate.second;
 292     if (NULL != tz) {
 293         offset0 = CFTimeZoneGetSecondsFromGMT(tz, at);
 294         offset1 = CFTimeZoneGetSecondsFromGMT(tz, at - offset0);
 295         at -= offset1;
 296     }
 297     return at;
 298 }
 299
 300 CFGregorianDate CFAbsoluteTimeGetGregorianDate(CFAbsoluteTime at, CFTimeZoneRef tz) {
 301     CFGregorianDate gdate;
 302     int64_t absolute, year;
 303     int8_t month, day;
 304     CFAbsoluteTime fixedat;
 305     if (NULL != tz) {
 306         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 307     }
 308     fixedat = at + (NULL != tz ? CFTimeZoneGetSecondsFromGMT(tz, at) : 0.0);
 309     absolute = (int64_t)floor(fixedat / 86400.0);
 310     __CFYMDFromAbsolute(absolute, &year, &month, &day);
 311     if (INT32_MAX - 2001 < year) year = INT32_MAX - 2001;
 312     gdate.year = year + 2001;
 313     gdate.month = month;
 314     gdate.day = day;
 315     gdate.hour = __CFDoubleModToInt(floor(fixedat / 3600.0), 24);
 316     gdate.minute = __CFDoubleModToInt(floor(fixedat / 60.0), 60);
 317     gdate.second = __CFDoubleMod(fixedat, 60);
 318     if (0.0 == gdate.second) gdate.second = 0.0;        // stomp out possible -0.0
 319     return gdate;
 320 }
 321
 322 /* Note that the units of years and months are not equal length, but are treated as such. */
 323 CFAbsoluteTime CFAbsoluteTimeAddGregorianUnits(CFAbsoluteTime at, CFTimeZoneRef tz, CFGregorianUnits units) {
 324     CFGregorianDate gdate;
 325     CFGregorianUnits working;
 326     CFAbsoluteTime candidate_at0, candidate_at1;
 327     uint8_t monthdays;
 328
 329     if (NULL != tz) {
 330         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 331     }
 332
 333     /* Most people seem to expect years, then months, then days, etc.
 334         to be added in that order.  Thus, 27 April + (4 days, 1 month)
 335         = 31 May, and not 1 June. This is also relatively predictable.
 336
 337         On another issue, months not being equal length, people also
 338         seem to expect late day-of-month clamping (don't clamp as you
 339         go through months), but clamp before adding in the days. Late
 340         clamping is also more predictable given random starting points
 341         and random numbers of months added (ie Jan 31 + 2 months could
 342         be March 28 or March 29 in different years with aggressive
 343         clamping). Proportionality (28 Feb + 1 month = 31 March) is
 344         also not expected.
 345
 346         Also, people don't expect time zone transitions to have any
 347         effect when adding years and/or months and/or days, only.
 348         Hours, minutes, and seconds, though, are added in as humans
 349         would experience the passing of that time. What this means
 350         is that if the date, after adding years, months, and days
 351         lands on some date, and then adding hours, minutes, and
 352         seconds crosses a time zone transition, the time zone
 353         transition is accounted for. If adding years, months, and
 354         days gets the date into a different time zone offset period,
 355         that transition is not taken into account.
 356     */
 357     gdate = CFAbsoluteTimeGetGregorianDate(at, tz);
 358     /* We must work in a CFGregorianUnits, because the fields in the CFGregorianDate can easily overflow */
 359     working.years = gdate.year;
 360     working.months = gdate.month;
 361     working.days = gdate.day;
 362     working.years += units.years;
 363     working.months += units.months;
 364     while (12 < working.months) {
 365         working.months -= 12;
 366         working.years += 1;
 367     }
 368     while (working.months < 1) {
 369         working.months += 12;
 370         working.years -= 1;
 371     }
 372     monthdays = __CFDaysInMonth(working.months, working.years - 2001, isleap(working.years - 2001));
 373     if (monthdays < working.days) {     /* Clamp day to new month */
 374         working.days = monthdays;
 375     }
 376     working.days += units.days;
 377     while (monthdays < working.days) {
 378         working.months += 1;
 379         if (12 < working.months) {
 380             working.months -= 12;
 381             working.years += 1;
 382         }
 383         working.days -= monthdays;
 384         monthdays = __CFDaysInMonth(working.months, working.years - 2001, isleap(working.years - 2001));
 385     }
 386     while (working.days < 1) {
 387         working.months -= 1;
 388         if (working.months < 1) {
 389             working.months += 12;
 390             working.years -= 1;
 391         }
 392         monthdays = __CFDaysInMonth(working.months, working.years - 2001, isleap(working.years - 2001));
 393         working.days += monthdays;
 394     }
 395     gdate.year = working.years;
 396     gdate.month = working.months;
 397     gdate.day = working.days;
 398     /* Roll in hours, minutes, and seconds */
 399     candidate_at0 = CFGregorianDateGetAbsoluteTime(gdate, tz);
 400     candidate_at1 = candidate_at0 + 3600.0 * units.hours + 60.0 * units.minutes + units.seconds;
 401     /* If summing in the hours, minutes, and seconds delta pushes us
 402      * into a new time zone offset, that will automatically be taken
 403      * care of by the fact that we just add the raw time above. To
 404      * undo that effect, we'd have to get the time zone offsets for
 405      * candidate_at0 and candidate_at1 here, and subtract the
 406      * difference (offset1 - offset0) from candidate_at1. */
 407     return candidate_at1;
 408 }
 409
 410 /* at1 - at2.  The only constraint here is that this needs to be the inverse
 411 of CFAbsoluteTimeByAddingGregorianUnits(), but that's a very rigid constraint.
 412 Unfortunately, due to the nonuniformity of the year and month units, this
 413 inversion essentially has to approximate until it finds the answer. */
 414 CFGregorianUnits CFAbsoluteTimeGetDifferenceAsGregorianUnits(CFAbsoluteTime at1, CFAbsoluteTime at2, CFTimeZoneRef tz, CFOptionFlags unitFlags) {
 415     const int32_t seconds[5] = {366 * 24 * 3600, 31 * 24 * 3600, 24 * 3600, 3600, 60};
 416     CFGregorianUnits units = {0, 0, 0, 0, 0, 0.0};
 417     CFAbsoluteTime atold, atnew = at2;
 418     int32_t idx, incr;
 419     incr = (at2 < at1) ? 1 : -1;
 420     /* Successive approximation: years, then months, then days, then hours, then minutes. */
 421     for (idx = 0; idx < 5; idx++) {
 422         if (unitFlags & (1 << idx)) {
 423             ((int32_t *)&units)[idx] = -3 * incr + (int32_t)((at1 - atnew) / seconds[idx]);
 424             do {
 425                 atold = atnew;
 426                 ((int32_t *)&units)[idx] += incr;
 427                 atnew = CFAbsoluteTimeAddGregorianUnits(at2, tz, units);
 428             } while ((1 == incr && atnew <= at1) || (-1 == incr && at1 <= atnew));
 429             ((int32_t *)&units)[idx] -= incr;
 430             atnew = atold;
 431         }
 432     }
 433     if (unitFlags & kCFGregorianUnitsSeconds) {
 434         units.seconds = at1 - atnew;
 435     }
 436     if (0.0 == units.seconds) units.seconds = 0.0;      // stomp out possible -0.0
 437     return units;
 438 }
 439
 440 SInt32 CFAbsoluteTimeGetDayOfWeek(CFAbsoluteTime at, CFTimeZoneRef tz) {
 441     int64_t absolute;
 442     CFAbsoluteTime fixedat;
 443     if (NULL != tz) {
 444         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 445     }
 446     fixedat = at + (NULL != tz ? CFTimeZoneGetSecondsFromGMT(tz, at) : 0.0);
 447     absolute = (int64_t)floor(fixedat / 86400.0);
 448     return (absolute < 0) ? ((absolute + 1) % 7 + 7) : (absolute % 7 + 1); /* Monday = 1, etc. */
 449 }
 450
 451 SInt32 CFAbsoluteTimeGetDayOfYear(CFAbsoluteTime at, CFTimeZoneRef tz) {
 452     CFAbsoluteTime fixedat;
 453     int64_t absolute, year;
 454     int8_t month, day;
 455     if (NULL != tz) {
 456         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 457     }
 458     fixedat = at + (NULL != tz ? CFTimeZoneGetSecondsFromGMT(tz, at) : 0.0);
 459     absolute = (int64_t)floor(fixedat / 86400.0);
 460     __CFYMDFromAbsolute(absolute, &year, &month, &day);
 461     return __CFDaysBeforeMonth(month, year, isleap(year)) + day;
 462 }
 463
 464 /* "the first week of a year is the one which includes the first Thursday" (ISO 8601) */
 465 SInt32 CFAbsoluteTimeGetWeekOfYear(CFAbsoluteTime at, CFTimeZoneRef tz) {
 466     int64_t absolute, year;
 467     int8_t month, day;
 468     CFAbsoluteTime fixedat;
 469     if (NULL != tz) {
 470         __CFGenericValidateType(tz, CFTimeZoneGetTypeID());
 471     }
 472     fixedat = at + (NULL != tz ? CFTimeZoneGetSecondsFromGMT(tz, at) : 0.0);
 473     absolute = (int64_t)floor(fixedat / 86400.0);
 474     __CFYMDFromAbsolute(absolute, &year, &month, &day);
 475     double absolute0101 = __CFAbsoluteFromYMD(year, 1, 1);
 476     int64_t dow0101 = __CFDoubleModToInt(absolute0101, 7) + 1;
 477     /* First three and last three days of a year can end up in a week of a different year */
 478     if (1 == month && day < 4) {
 479         if ((day < 4 && 5 == dow0101) || (day < 3 && 6 == dow0101) || (day < 2 && 7 == dow0101)) {
 480             return 53;
 481         }
 482     }
 483     if (12 == month && 28 < day) {
 484         double absolute20101 = __CFAbsoluteFromYMD(year + 1, 1, 1);
 485         int64_t dow20101 = __CFDoubleModToInt(absolute20101, 7) + 1;
 486         if ((28 < day && 4 == dow20101) || (29 < day && 3 == dow20101) || (30 < day && 2 == dow20101)) {
 487             return 1;
 488         }
 489     }
 490     /* Days into year, plus a week-shifting correction, divided by 7. First week is 1. */
 491     return (__CFDaysBeforeMonth(month, year, isleap(year)) + day + (dow0101 - 11) % 7 + 2) / 7 + 1;
 492 }
 493
 494