ICU-22991 Simplified Grego code

Use timeToFields instead of dayToFields

ICU-22991 Revert back gregoimp interface change

icu4c/source/i18n/chnsecal.cpp

diff --git a/icu4c/source/i18n/chnsecal.cpp b/icu4c/source/i18n/chnsecal.cpp
index 8257bba..fdb8915 100644
--- a/icu4c/source/i18n/chnsecal.cpp
+++ b/icu4c/source/i18n/chnsecal.cpp
@@ -339,12 +339,10 @@ int64_t ChineseCalendar::handleComputeMonthStart(int32_t eyear, int32_t month, U
     // If the month is out of range, adjust it into range, and
     // modify the extended year value accordingly.
     if (month < 0 || month > 11) {
-        double m = month;
-        if (uprv_add32_overflow(eyear, ClockMath::floorDivide(m, 12.0, &m), &eyear)) {
+        if (uprv_add32_overflow(eyear, ClockMath::floorDivide(month, 12, &month), &eyear)) {
             status = U_ILLEGAL_ARGUMENT_ERROR;
             return 0;
         }
-        month = static_cast<int32_t>(m);
     }
 
     const Setting setting = getSetting(status);

icu4c/source/i18n/gregoimp.cpp

diff --git a/icu4c/source/i18n/gregoimp.cpp b/icu4c/source/i18n/gregoimp.cpp
index 161897b..03bf9d2 100644
--- a/icu4c/source/i18n/gregoimp.cpp
+++ b/icu4c/source/i18n/gregoimp.cpp
@@ -203,16 +203,21 @@ void Grego::timeToFields(UDate time, int32_t& year, int8_t& month,
 void Grego::timeToFields(UDate time, int32_t& year, int8_t& month,
                         int8_t& dom, int8_t& dow, int16_t& doy, int32_t& mid, UErrorCode& status) {
     if (U_FAILURE(status)) return;
-    double millisInDay;
-    double day = ClockMath::floorDivide(static_cast<double>(time), static_cast<double>(U_MILLIS_PER_DAY), &millisInDay);
-    mid = static_cast<int32_t>(millisInDay);
+    double day = ClockMath::floorDivide(time, U_MILLIS_PER_DAY, &mid);
+    if (day > INT32_MAX || day < INT32_MIN) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return;
+    }
     dayToFields(day, year, month, dom, dow, doy, status);
 }
 
 int32_t Grego::timeToYear(UDate time, UErrorCode& status) {
     if (U_FAILURE(status)) return 0;
-    double millisInDay;
-    int32_t day = ClockMath::floorDivide(static_cast<double>(time), static_cast<double>(U_MILLIS_PER_DAY), &millisInDay);
+    double day = ClockMath::floorDivide(time, double(U_MILLIS_PER_DAY));
+    if (day > INT32_MAX || day < INT32_MIN) {
+        status = U_ILLEGAL_ARGUMENT_ERROR;
+        return 0;
+    }
     return Grego::dayToYear(day, status);
 }
 

icu4c/source/i18n/olsontz.cpp

diff --git a/icu4c/source/i18n/olsontz.cpp b/icu4c/source/i18n/olsontz.cpp
index c795e9a..7826d47 100644
--- a/icu4c/source/i18n/olsontz.cpp
+++ b/icu4c/source/i18n/olsontz.cpp
@@ -436,11 +436,11 @@ int32_t OlsonTimeZone::getRawOffset() const {
 
 #if defined U_DEBUG_TZ
 void printTime(double ms) {
-            int32_t year, month, dom, dow;
-            double millis=0;
-            double days = ClockMath::floorDivide(((double)ms), (double)U_MILLIS_PER_DAY, millis);
-            
-            Grego::dayToFields(days, year, month, dom, dow);
+            int32_t year;
+            int8_t month, dom, dow;
+            int32_t millis=0;
+            UErrorCode status = U_ZERO_ERROR;
+            Grego::timeToFields(ms, year, month, dom, dow, millis, status);
             U_DEBUG_TZ_MSG(("   getHistoricalOffset:  time %.1f (%04d.%02d.%02d+%.1fh)\n", ms,
                             year, month+1, dom, (millis/kOneHour)));
     }

icu4c/source/i18n/simpletz.cpp

diff --git a/icu4c/source/i18n/simpletz.cpp b/icu4c/source/i18n/simpletz.cpp
index ec80db4..3f3b236 100644
--- a/icu4c/source/i18n/simpletz.cpp
+++ b/icu4c/source/i18n/simpletz.cpp
@@ -520,14 +520,8 @@ SimpleTimeZone::getOffsetFromLocal(UDate date, UTimeZoneLocalOption nonExistingT
     rawOffsetGMT = getRawOffset();
     int32_t year, millis;
     int8_t month, dom, dow;
-    double dday = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-    if (dday > INT32_MAX || dday < INT32_MIN) {
-        status = U_ILLEGAL_ARGUMENT_ERROR;
-        return;
-    }
-    int32_t day = dday;
 
-    Grego::dayToFields(day, year, month, dom, dow, status);
+    Grego::timeToFields(date, year, month, dom, dow, millis, status);
     if (U_FAILURE(status)) return;
 
     savingsDST = getOffset(GregorianCalendar::AD, year, month, dom,
@@ -555,8 +549,7 @@ SimpleTimeZone::getOffsetFromLocal(UDate date, UTimeZoneLocalOption nonExistingT
         }
     }
     if (recalc) {
-        day = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-        Grego::dayToFields(day, year, month, dom, dow, status);
+        Grego::timeToFields(date, year, month, dom, dow, millis, status);
         if (U_FAILURE(status)) return;
         savingsDST = getOffset(GregorianCalendar::AD, year, month, dom,
                           static_cast<uint8_t>(dow), millis,

icu4c/source/i18n/timezone.cpp

diff --git a/icu4c/source/i18n/timezone.cpp b/icu4c/source/i18n/timezone.cpp
index e2cf359..bc3a642 100644
--- a/icu4c/source/i18n/timezone.cpp
+++ b/icu4c/source/i18n/timezone.cpp
@@ -732,14 +732,7 @@ void TimeZone::getOffset(UDate date, UBool local, int32_t& rawOffset,
     for (int32_t pass=0; ; ++pass) {
         int32_t year, millis;
         int8_t month, dom, dow;
-        double day = ClockMath::floorDivide(date, U_MILLIS_PER_DAY, &millis);
-
-        // out of the range
-        if (day < INT32_MIN || day > INT32_MAX) {
-            ec = U_ILLEGAL_ARGUMENT_ERROR;
-            return;
-        }
-        Grego::dayToFields(day, year, month, dom, dow, ec);
+        Grego::timeToFields(date, year, month, dom, dow, millis, ec);
         if (U_FAILURE(ec)) return;
 
         dstOffset = getOffset(GregorianCalendar::AD, year, month, dom,