1// © 2016 and later: Unicode, Inc. and others.
2// License & terms of use: http://www.unicode.org/copyright.html
3/*
4 **********************************************************************
5 * Copyright (c) 2003-2008, International Business Machines
6 * Corporation and others.  All Rights Reserved.
7 **********************************************************************
8 * Author: Alan Liu
9 * Created: September 2 2003
10 * Since: ICU 2.8
11 **********************************************************************
12 */
13
14#include "gregoimp.h"
15
16#if !UCONFIG_NO_FORMATTING
17
18#include "unicode/ucal.h"
19#include "uresimp.h"
20#include "cstring.h"
21#include "uassert.h"
22
23U_NAMESPACE_BEGIN
24
25int32_t ClockMath::floorDivide(int32_t numerator, int32_t denominator) {
26    return (numerator >= 0) ?
27        numerator / denominator : ((numerator + 1) / denominator) - 1;
28}
29
30int64_t ClockMath::floorDivide(int64_t numerator, int64_t denominator) {
31    return (numerator >= 0) ?
32        numerator / denominator : ((numerator + 1) / denominator) - 1;
33}
34
35int32_t ClockMath::floorDivide(double numerator, int32_t denominator,
36                          int32_t* remainder) {
37    // For an integer n and representable ⌊x/n⌋, ⌊RN(x/n)⌋=⌊x/n⌋, where RN is
38    // rounding to nearest.
39    double quotient = uprv_floor(numerator / denominator);
40    if (remainder != nullptr) {
41      // For doubles x and n, where n is an integer and ⌊x+n⌋ < 2³¹, the
42      // expression `(int32_t) (x + n)` evaluated with rounding to nearest
43      // differs from ⌊x+n⌋ if 0 < ⌈x⌉−x ≪ x+n, as `x + n` is rounded up to
44      // n+⌈x⌉ = ⌊x+n⌋ + 1.  Rewriting it as ⌊x⌋+n makes the addition exact.
45      *remainder = (int32_t) (uprv_floor(numerator) - (quotient * denominator));
46    }
47    return (int32_t) quotient;
48}
49
50double ClockMath::floorDivide(double dividend, double divisor,
51                         double* remainder) {
52    // Only designed to work for positive divisors
53    U_ASSERT(divisor > 0);
54    double quotient = floorDivide(dividend, divisor);
55    double r = dividend - (quotient * divisor);
56    // N.B. For certain large dividends, on certain platforms, there
57    // is a bug such that the quotient is off by one.  If you doubt
58    // this to be true, set a breakpoint below and run cintltst.
59    if (r < 0 || r >= divisor) {
60        // E.g. 6.7317038241449352e+022 / 86400000.0 is wrong on my
61        // machine (too high by one).  4.1792057231752762e+024 /
62        // 86400000.0 is wrong the other way (too low).
63        double q = quotient;
64        quotient += (r < 0) ? -1 : +1;
65        if (q == quotient) {
66            // For quotients > ~2^53, we won't be able to add or
67            // subtract one, since the LSB of the mantissa will be >
68            // 2^0; that is, the exponent (base 2) will be larger than
69            // the length, in bits, of the mantissa.  In that case, we
70            // can't give a correct answer, so we set the remainder to
71            // zero.  This has the desired effect of making extreme
72            // values give back an approximate answer rather than
73            // crashing.  For example, UDate values above a ~10^25
74            // might all have a time of midnight.
75            r = 0;
76        } else {
77            r = dividend - (quotient * divisor);
78        }
79    }
80    U_ASSERT(0 <= r && r < divisor);
81    if (remainder != nullptr) {
82        *remainder = r;
83    }
84    return quotient;
85}
86
87const int32_t JULIAN_1_CE    = 1721426; // January 1, 1 CE Gregorian
88const int32_t JULIAN_1970_CE = 2440588; // January 1, 1970 CE Gregorian
89
90const int16_t Grego::DAYS_BEFORE[24] =
91    {0,31,59,90,120,151,181,212,243,273,304,334,
92     0,31,60,91,121,152,182,213,244,274,305,335};
93
94const int8_t Grego::MONTH_LENGTH[24] =
95    {31,28,31,30,31,30,31,31,30,31,30,31,
96     31,29,31,30,31,30,31,31,30,31,30,31};
97
98double Grego::fieldsToDay(int32_t year, int32_t month, int32_t dom) {
99
100    int32_t y = year - 1;
101
102    double julian = 365 * y + ClockMath::floorDivide(y, 4) + (JULIAN_1_CE - 3) + // Julian cal
103        ClockMath::floorDivide(y, 400) - ClockMath::floorDivide(y, 100) + 2 + // => Gregorian cal
104        DAYS_BEFORE[month + (isLeapYear(year) ? 12 : 0)] + dom; // => month/dom
105
106    return julian - JULIAN_1970_CE; // JD => epoch day
107}
108
109void Grego::dayToFields(double day, int32_t& year, int32_t& month,
110                        int32_t& dom, int32_t& dow, int32_t& doy) {
111
112    // Convert from 1970 CE epoch to 1 CE epoch (Gregorian calendar)
113    day += JULIAN_1970_CE - JULIAN_1_CE;
114
115    // Convert from the day number to the multiple radix
116    // representation.  We use 400-year, 100-year, and 4-year cycles.
117    // For example, the 4-year cycle has 4 years + 1 leap day; giving
118    // 1461 == 365*4 + 1 days.
119    int32_t n400 = ClockMath::floorDivide(day, 146097, &doy); // 400-year cycle length
120    int32_t n100 = ClockMath::floorDivide(doy, 36524, &doy); // 100-year cycle length
121    int32_t n4   = ClockMath::floorDivide(doy, 1461, &doy); // 4-year cycle length
122    int32_t n1   = ClockMath::floorDivide(doy, 365, &doy);
123    year = 400*n400 + 100*n100 + 4*n4 + n1;
124    if (n100 == 4 || n1 == 4) {
125        doy = 365; // Dec 31 at end of 4- or 400-year cycle
126    } else {
127        ++year;
128    }
129
130    UBool isLeap = isLeapYear(year);
131
132    // Gregorian day zero is a Monday.
133    dow = (int32_t) uprv_fmod(day + 1, 7);
134    dow += (dow < 0) ? (UCAL_SUNDAY + 7) : UCAL_SUNDAY;
135
136    // Common Julian/Gregorian calculation
137    int32_t correction = 0;
138    int32_t march1 = isLeap ? 60 : 59; // zero-based DOY for March 1
139    if (doy >= march1) {
140        correction = isLeap ? 1 : 2;
141    }
142    month = (12 * (doy + correction) + 6) / 367; // zero-based month
143    dom = doy - DAYS_BEFORE[month + (isLeap ? 12 : 0)] + 1; // one-based DOM
144    doy++; // one-based doy
145}
146
147void Grego::timeToFields(UDate time, int32_t& year, int32_t& month,
148                        int32_t& dom, int32_t& dow, int32_t& doy, int32_t& mid) {
149    double millisInDay;
150    double day = ClockMath::floorDivide((double)time, (double)U_MILLIS_PER_DAY, &millisInDay);
151    mid = (int32_t)millisInDay;
152    dayToFields(day, year, month, dom, dow, doy);
153}
154
155int32_t Grego::dayOfWeek(double day) {
156    int32_t dow;
157    ClockMath::floorDivide(day + int{UCAL_THURSDAY}, 7, &dow);
158    return (dow == 0) ? UCAL_SATURDAY : dow;
159}
160
161int32_t Grego::dayOfWeekInMonth(int32_t year, int32_t month, int32_t dom) {
162    int32_t weekInMonth = (dom + 6)/7;
163    if (weekInMonth == 4) {
164        if (dom + 7 > monthLength(year, month)) {
165            weekInMonth = -1;
166        }
167    } else if (weekInMonth == 5) {
168        weekInMonth = -1;
169    }
170    return weekInMonth;
171}
172
173U_NAMESPACE_END
174
175#endif
176//eof
177