From f07320ca1b7473b36bdc2b6cbc0841d7f024ae4e Mon Sep 17 00:00:00 2001
From: Frank Tang <ftang@chromium.org>
Date: Wed, 27 Nov 2024 13:40:54 -0800
Subject: [PATCH] ICU-22983 Fix DecimalQuantity::shiftLeft ubsan issue

---
 icu4c/source/i18n/number_decimalquantity.cpp | 2 +-
 icu4c/source/test/intltest/numfmtst.cpp      | 5 +++++
 icu4c/source/test/intltest/numfmtst.h        | 1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/icu4c/source/i18n/number_decimalquantity.cpp b/icu4c/source/i18n/number_decimalquantity.cpp
index f9350d5d5cc8..ca1dacd3579d 100644
--- a/icu4c/source/i18n/number_decimalquantity.cpp
+++ b/icu4c/source/i18n/number_decimalquantity.cpp
@@ -1133,7 +1133,7 @@ void DecimalQuantity::setDigitPos(int32_t position, int8_t value) {
 }
 
 void DecimalQuantity::shiftLeft(int32_t numDigits) {
-    if (!usingBytes && precision + numDigits > 16) {
+    if (!usingBytes && precision + numDigits >= 16) {
         switchStorage();
     }
     if (usingBytes) {
diff --git a/icu4c/source/test/intltest/numfmtst.cpp b/icu4c/source/test/intltest/numfmtst.cpp
index a37111a8540d..ede924722952 100644
--- a/icu4c/source/test/intltest/numfmtst.cpp
+++ b/icu4c/source/test/intltest/numfmtst.cpp
@@ -253,6 +253,7 @@ void NumberFormatTest::runIndexedTest( int32_t index, UBool exec, const char* &n
   TESTCASE_AUTO(Test10997_FormatCurrency);
   TESTCASE_AUTO(Test21556_CurrencyAsDecimal);
   TESTCASE_AUTO(Test22088_Ethiopic);
+  TESTCASE_AUTO(Test22983_LongFraction);
   TESTCASE_AUTO_END;
 }
 
@@ -10161,5 +10162,9 @@ void NumberFormatTest::Test22088_Ethiopic() {
         assertEquals("Wrong result with UNUM_NUMBERING_SYSTEM and English", u"123", nf3->format(123, result));
     }
 }
+void NumberFormatTest::Test22983_LongFraction() {
+    IcuTestErrorCode status(*this, "Test22983_LongFraction");
+    DecimalFormat df(u"0.0000000000000001", status);
+}
 
 #endif /* #if !UCONFIG_NO_FORMATTING */
diff --git a/icu4c/source/test/intltest/numfmtst.h b/icu4c/source/test/intltest/numfmtst.h
index 5bdbc131cda3..10dd3386d4c9 100644
--- a/icu4c/source/test/intltest/numfmtst.h
+++ b/icu4c/source/test/intltest/numfmtst.h
@@ -309,6 +309,7 @@ class NumberFormatTest: public CalendarTimeZoneTest {
     void Test10997_FormatCurrency();
     void Test21556_CurrencyAsDecimal();
     void Test22088_Ethiopic();
+    void Test22983_LongFraction();
 
  private:
     UBool testFormattableAsUFormattable(const char *file, int line, Formattable &f);