From 05a6420ee35773e3a877e4003179c97696f54425 Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Mon, 6 Jan 2025 16:02:00 -0800
Subject: [PATCH] ICU-22991 Reduce Calendar object size

Gregorian monthOfYear, dayOfMonth only need one byte
dayOfYear only need two bytes to store.
---
 icu4c/source/i18n/calendar.cpp       | 13 ++++++++++---
 icu4c/source/i18n/unicode/calendar.h | 14 +++++++-------
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/icu4c/source/i18n/calendar.cpp b/icu4c/source/i18n/calendar.cpp
index ddff6255cd85..0dd0755589d8 100644
--- a/icu4c/source/i18n/calendar.cpp
+++ b/icu4c/source/i18n/calendar.cpp
@@ -1544,9 +1544,16 @@ void Calendar::computeGregorianFields(int32_t julianDay, UErrorCode& ec) {
         ec = U_ILLEGAL_ARGUMENT_ERROR;
         return;
     }
-    Grego::dayToFields(julianDay, fGregorianYear, fGregorianMonth,
-                       fGregorianDayOfMonth, gregorianDayOfWeekUnused,
-                       fGregorianDayOfYear, ec);
+    int32_t gregorianMonth, gregorianDayOfMonth, gregorianDayOfYear;
+    Grego::dayToFields(julianDay, fGregorianYear, gregorianMonth,
+                       gregorianDayOfMonth, gregorianDayOfWeekUnused,
+                       gregorianDayOfYear, ec);
+    U_ASSERT(gregorianMonth <= 12);
+    U_ASSERT(gregorianDayOfMonth <= 31);
+    U_ASSERT(gregorianDayOfYear <= 366);
+    fGregorianMonth = gregorianMonth;
+    fGregorianDayOfMonth = gregorianDayOfMonth;
+    fGregorianDayOfYear = gregorianDayOfYear;
 }
 
 /**
diff --git a/icu4c/source/i18n/unicode/calendar.h b/icu4c/source/i18n/unicode/calendar.h
index 0c36185a85c3..bed5bfeef075 100644
--- a/icu4c/source/i18n/unicode/calendar.h
+++ b/icu4c/source/i18n/unicode/calendar.h
@@ -2256,21 +2256,21 @@ class U_I18N_API Calendar : public UObject {
      * returned by getGregorianMonth().
      * @see #computeGregorianFields
      */
-    int32_t fGregorianMonth;
+    int8_t fGregorianMonth;
 
     /**
-     * The Gregorian day of the year, as computed by
-     * computeGregorianFields() and returned by getGregorianDayOfYear().
+     * The Gregorian day of the month, as computed by
+     * computeGregorianFields() and returned by getGregorianDayOfMonth().
      * @see #computeGregorianFields
      */
-    int32_t fGregorianDayOfYear;
+    int8_t fGregorianDayOfMonth;
 
     /**
-     * The Gregorian day of the month, as computed by
-     * computeGregorianFields() and returned by getGregorianDayOfMonth().
+     * The Gregorian day of the year, as computed by
+     * computeGregorianFields() and returned by getGregorianDayOfYear().
      * @see #computeGregorianFields
      */
-    int32_t fGregorianDayOfMonth;
+    int16_t fGregorianDayOfYear;
 
     /* calculations */