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diff --git a/intl/icu/source/i18n/gregoimp.cpp b/intl/icu/source/i18n/gregoimp.cpp
new file mode 100644
index 0000000000..31b5aeed83
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+++ b/intl/icu/source/i18n/gregoimp.cpp
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+// © 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+ **********************************************************************
+ * Copyright (c) 2003-2008, International Business Machines
+ * Corporation and others.  All Rights Reserved.
+ **********************************************************************
+ * Author: Alan Liu
+ * Created: September 2 2003
+ * Since: ICU 2.8
+ **********************************************************************
+ */
+
+#include "gregoimp.h"
+
+#if !UCONFIG_NO_FORMATTING
+
+#include "unicode/ucal.h"
+#include "uresimp.h"
+#include "cstring.h"
+#include "uassert.h"
+
+U_NAMESPACE_BEGIN
+
+int32_t ClockMath::floorDivide(int32_t numerator, int32_t denominator) {
+    return (numerator >= 0) ?
+        numerator / denominator : ((numerator + 1) / denominator) - 1;
+}
+
+int64_t ClockMath::floorDivide(int64_t numerator, int64_t denominator) {
+    return (numerator >= 0) ?
+        numerator / denominator : ((numerator + 1) / denominator) - 1;
+}
+
+int32_t ClockMath::floorDivide(double numerator, int32_t denominator,
+                          int32_t* remainder) {
+    // For an integer n and representable ⌊x/n⌋, ⌊RN(x/n)⌋=⌊x/n⌋, where RN is
+    // rounding to nearest.
+    double quotient = uprv_floor(numerator / denominator);
+    if (remainder != nullptr) {
+      // For doubles x and n, where n is an integer and ⌊x+n⌋ < 2³¹, the
+      // expression `(int32_t) (x + n)` evaluated with rounding to nearest
+      // differs from ⌊x+n⌋ if 0 < ⌈x⌉−x ≪ x+n, as `x + n` is rounded up to
+      // n+⌈x⌉ = ⌊x+n⌋ + 1.  Rewriting it as ⌊x⌋+n makes the addition exact.
+      *remainder = (int32_t) (uprv_floor(numerator) - (quotient * denominator));
+    }
+    return (int32_t) quotient;
+}
+
+double ClockMath::floorDivide(double dividend, double divisor,
+                         double* remainder) {
+    // Only designed to work for positive divisors
+    U_ASSERT(divisor > 0);
+    double quotient = floorDivide(dividend, divisor);
+    double r = dividend - (quotient * divisor);
+    // N.B. For certain large dividends, on certain platforms, there
+    // is a bug such that the quotient is off by one.  If you doubt
+    // this to be true, set a breakpoint below and run cintltst.
+    if (r < 0 || r >= divisor) {
+        // E.g. 6.7317038241449352e+022 / 86400000.0 is wrong on my
+        // machine (too high by one).  4.1792057231752762e+024 /
+        // 86400000.0 is wrong the other way (too low).
+        double q = quotient;
+        quotient += (r < 0) ? -1 : +1;
+        if (q == quotient) {
+            // For quotients > ~2^53, we won't be able to add or
+            // subtract one, since the LSB of the mantissa will be >
+            // 2^0; that is, the exponent (base 2) will be larger than
+            // the length, in bits, of the mantissa.  In that case, we
+            // can't give a correct answer, so we set the remainder to
+            // zero.  This has the desired effect of making extreme
+            // values give back an approximate answer rather than
+            // crashing.  For example, UDate values above a ~10^25
+            // might all have a time of midnight.
+            r = 0;
+        } else {
+            r = dividend - (quotient * divisor);
+        }
+    }
+    U_ASSERT(0 <= r && r < divisor);
+    if (remainder != nullptr) {
+        *remainder = r;
+    }
+    return quotient;
+}
+
+const int32_t JULIAN_1_CE    = 1721426; // January 1, 1 CE Gregorian
+const int32_t JULIAN_1970_CE = 2440588; // January 1, 1970 CE Gregorian
+
+const int16_t Grego::DAYS_BEFORE[24] =
+    {0,31,59,90,120,151,181,212,243,273,304,334,
+     0,31,60,91,121,152,182,213,244,274,305,335};
+
+const int8_t Grego::MONTH_LENGTH[24] =
+    {31,28,31,30,31,30,31,31,30,31,30,31,
+     31,29,31,30,31,30,31,31,30,31,30,31};
+
+double Grego::fieldsToDay(int32_t year, int32_t month, int32_t dom) {
+
+    int32_t y = year - 1;
+
+    double julian = 365 * y + ClockMath::floorDivide(y, 4) + (JULIAN_1_CE - 3) + // Julian cal
+        ClockMath::floorDivide(y, 400) - ClockMath::floorDivide(y, 100) + 2 + // => Gregorian cal
+        DAYS_BEFORE[month + (isLeapYear(year) ? 12 : 0)] + dom; // => month/dom
+
+    return julian - JULIAN_1970_CE; // JD => epoch day
+}
+
+void Grego::dayToFields(double day, int32_t& year, int32_t& month,
+                        int32_t& dom, int32_t& dow, int32_t& doy) {
+
+    // Convert from 1970 CE epoch to 1 CE epoch (Gregorian calendar)
+    day += JULIAN_1970_CE - JULIAN_1_CE;
+
+    // Convert from the day number to the multiple radix
+    // representation.  We use 400-year, 100-year, and 4-year cycles.
+    // For example, the 4-year cycle has 4 years + 1 leap day; giving
+    // 1461 == 365*4 + 1 days.
+    int32_t n400 = ClockMath::floorDivide(day, 146097, &doy); // 400-year cycle length
+    int32_t n100 = ClockMath::floorDivide(doy, 36524, &doy); // 100-year cycle length
+    int32_t n4   = ClockMath::floorDivide(doy, 1461, &doy); // 4-year cycle length
+    int32_t n1   = ClockMath::floorDivide(doy, 365, &doy);
+    year = 400*n400 + 100*n100 + 4*n4 + n1;
+    if (n100 == 4 || n1 == 4) {
+        doy = 365; // Dec 31 at end of 4- or 400-year cycle
+    } else {
+        ++year;
+    }
+    
+    UBool isLeap = isLeapYear(year);
+    
+    // Gregorian day zero is a Monday.
+    dow = (int32_t) uprv_fmod(day + 1, 7);
+    dow += (dow < 0) ? (UCAL_SUNDAY + 7) : UCAL_SUNDAY;
+
+    // Common Julian/Gregorian calculation
+    int32_t correction = 0;
+    int32_t march1 = isLeap ? 60 : 59; // zero-based DOY for March 1
+    if (doy >= march1) {
+        correction = isLeap ? 1 : 2;
+    }
+    month = (12 * (doy + correction) + 6) / 367; // zero-based month
+    dom = doy - DAYS_BEFORE[month + (isLeap ? 12 : 0)] + 1; // one-based DOM
+    doy++; // one-based doy
+}
+
+void Grego::timeToFields(UDate time, int32_t& year, int32_t& month,
+                        int32_t& dom, int32_t& dow, int32_t& doy, int32_t& mid) {
+    double millisInDay;
+    double day = ClockMath::floorDivide((double)time, (double)U_MILLIS_PER_DAY, &millisInDay);
+    mid = (int32_t)millisInDay;
+    dayToFields(day, year, month, dom, dow, doy);
+}
+
+int32_t Grego::dayOfWeek(double day) {
+    int32_t dow;
+    ClockMath::floorDivide(day + int{UCAL_THURSDAY}, 7, &dow);
+    return (dow == 0) ? UCAL_SATURDAY : dow;
+}
+
+int32_t Grego::dayOfWeekInMonth(int32_t year, int32_t month, int32_t dom) {
+    int32_t weekInMonth = (dom + 6)/7;
+    if (weekInMonth == 4) {
+        if (dom + 7 > monthLength(year, month)) {
+            weekInMonth = -1;
+        }
+    } else if (weekInMonth == 5) {
+        weekInMonth = -1;
+    }
+    return weekInMonth;
+}
+
+U_NAMESPACE_END
+
+#endif
+//eof