From 26734536f7be53647643a5d9845a5caee77cc1ff Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Mon, 30 Dec 2024 20:33:10 -0800
Subject: [PATCH] ICU-22991 Reduce fStamp to 8 bits

Reduce 24x3=72 bytes per Calendar object by changing
from 32 bits integer to 8 bits integer for the stamp array.
---
 icu4c/source/i18n/calendar.cpp                 | 18 ++++++------------
 icu4c/source/i18n/unicode/calendar.h           |  6 +++---
 .../main/java/com/ibm/icu/util/Calendar.java   | 14 +++++++-------
 3 files changed, 16 insertions(+), 22 deletions(-)

diff --git a/icu4c/source/i18n/calendar.cpp b/icu4c/source/i18n/calendar.cpp
index ca3de520c8f2..a1d80af5f011 100644
--- a/icu4c/source/i18n/calendar.cpp
+++ b/icu4c/source/i18n/calendar.cpp
@@ -156,7 +156,7 @@ U_CFUNC void ucal_dump(UCalendar* cal) {
 #endif
 
 /* Max value for stamp allowable before recalculation */
-#define STAMP_MAX 10000
+#define STAMP_MAX 127
 
 static const char * const gCalTypes[] = {
     "gregorian",
@@ -1166,12 +1166,8 @@ Calendar::setTimeInMillis( double millis, UErrorCode& status ) {
     fAreFieldsSet = fAreAllFieldsSet = false;
     fIsTimeSet = fAreFieldsVirtuallySet = true;
 
-    for (int32_t i=0; i<UCAL_FIELD_COUNT; ++i) {
-        fFields[i]     = 0;
-        fStamp[i]     = kUnset;
-    }
-
-
+    uprv_memset(fFields, 0, sizeof(fFields));
+    uprv_memset(fStamp, 0, sizeof(fStamp));
 }
 
 // -------------------------------------
@@ -1206,7 +1202,7 @@ Calendar::set(UCalendarDateFields field, int32_t value)
         computeFields(ec);
     }
     fFields[field]     = value;
-    /* Ensure that the fNextStamp value doesn't go pass max value for int32_t */
+    /* Ensure that the fNextStamp value doesn't go pass max value for int8_t */
     if (fNextStamp == STAMP_MAX) {
         recalculateStamp();
     }
@@ -1267,10 +1263,8 @@ void Calendar::setRelatedYear(int32_t year)
 void
 Calendar::clear()
 {
-    for (int32_t i=0; i<UCAL_FIELD_COUNT; ++i) {
-        fFields[i]     = 0; // Must do this; other code depends on it
-        fStamp[i]     = kUnset;
-    }
+    uprv_memset(fFields, 0, sizeof(fFields));
+    uprv_memset(fStamp, 0, sizeof(fStamp));
     fIsTimeSet = fAreFieldsSet = fAreAllFieldsSet = fAreFieldsVirtuallySet = false;
     // fTime is not 'cleared' - may be used if no fields are set.
 }
diff --git a/icu4c/source/i18n/unicode/calendar.h b/icu4c/source/i18n/unicode/calendar.h
index 1d2104be607d..9be0a2bb8dc5 100644
--- a/icu4c/source/i18n/unicode/calendar.h
+++ b/icu4c/source/i18n/unicode/calendar.h
@@ -1951,9 +1951,9 @@ class U_I18N_API Calendar : public UObject {
     /**
      * Pseudo-time-stamps which specify when each field was set. There
      * are two special values, UNSET and INTERNALLY_SET. Values from
-     * MINIMUM_USER_SET to Integer.MAX_VALUE are legal user set values.
+     * MINIMUM_USER_SET to 127 are legal user set values.
      */
-    int32_t        fStamp[UCAL_FIELD_COUNT];
+    int8_t        fStamp[UCAL_FIELD_COUNT];
 
 protected:
     /**
@@ -2169,7 +2169,7 @@ class U_I18N_API Calendar : public UObject {
     /**
      * The next available value for fStamp[]
      */
-    int32_t fNextStamp;// = MINIMUM_USER_STAMP;
+    int8_t fNextStamp;// = MINIMUM_USER_STAMP;
 
     /**
      * Recalculates the time stamp array (fStamp).
diff --git a/icu4j/main/core/src/main/java/com/ibm/icu/util/Calendar.java b/icu4j/main/core/src/main/java/com/ibm/icu/util/Calendar.java
index 47e4d6a205fb..e1009c75466d 100644
--- a/icu4j/main/core/src/main/java/com/ibm/icu/util/Calendar.java
+++ b/icu4j/main/core/src/main/java/com/ibm/icu/util/Calendar.java
@@ -1355,9 +1355,9 @@ public abstract class Calendar implements Serializable, Cloneable, Comparable<Ca
     /**
      * Pseudo-time-stamps which specify when each field was set. There
      * are two special values, UNSET and INTERNALLY_SET. Values from
-     * MINIMUM_USER_SET to Integer.MAX_VALUE are legal user set values.
+     * MINIMUM_USER_SET to Byte.MAX_VALUE are legal user set values.
      */
-    private transient int           stamp[];
+    private transient byte           stamp[];
 
     /**
      * The currently set time for this calendar, expressed in milliseconds after
@@ -1507,10 +1507,10 @@ public abstract class Calendar implements Serializable, Cloneable, Comparable<Ca
      * The next available value for <code>stamp[]</code>, an internal array.
      * @serial
      */
-    private transient int             nextStamp = MINIMUM_USER_STAMP;
+    private transient byte             nextStamp = MINIMUM_USER_STAMP;
 
     /* Max value for stamp allowable before recalculation */
-    private static int STAMP_MAX = 10000;
+    private static byte STAMP_MAX = Byte.MAX_VALUE;
 
     // the internal serial version which says which version was written
     // - 0 (default) for version up to JDK 1.1.5
@@ -1684,7 +1684,7 @@ private void setCalendarLocale(ULocale locale) {
 
     private void recalculateStamp() {
         int index;
-        int currentValue;
+        byte currentValue;
         int j, i;
 
         nextStamp = 1;
@@ -1721,7 +1721,7 @@ private void initInternal()
             throw new IllegalStateException("Invalid fields[]");
         }
         ///CLOVER:ON
-        stamp = new int[fields.length];
+        stamp = new byte[fields.length];
         int mask = (1 << ERA) |
                 (1 << YEAR) |
                 (1 << MONTH) |
@@ -4904,7 +4904,7 @@ public Object clone()
             Calendar other = (Calendar) super.clone();
 
             other.fields = new int[fields.length];
-            other.stamp = new int[fields.length];
+            other.stamp = new byte[fields.length];
             System.arraycopy(this.fields, 0, other.fields, 0, fields.length);
             System.arraycopy(this.stamp, 0, other.stamp, 0, fields.length);