From 3328b4ecf225f95edfce6ab848dcfb62ddc1aaff Mon Sep 17 00:00:00 2001
From: Sonia Zaldana Calles <szaldana@openjdk.org>
Date: Tue, 19 Nov 2024 19:13:09 +0000
Subject: [PATCH] 8343700: ceil_log2 should not loop endlessly

Reviewed-by: shade, kbarrett, aph, stuefe
---
 src/hotspot/share/classfile/dictionary.cpp    |  2 +-
 src/hotspot/share/utilities/powerOfTwo.hpp    |  9 ++--
 .../gtest/utilities/test_powerOfTwo.cpp       | 43 ++++++++++++++++++-
 3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/src/hotspot/share/classfile/dictionary.cpp b/src/hotspot/share/classfile/dictionary.cpp
index 73d58ac3687..92f362860eb 100644
--- a/src/hotspot/share/classfile/dictionary.cpp
+++ b/src/hotspot/share/classfile/dictionary.cpp
@@ -44,7 +44,7 @@ const size_t REHASH_LEN = 100;
 Dictionary::Dictionary(ClassLoaderData* loader_data, size_t table_size)
   : _number_of_entries(0), _loader_data(loader_data) {
 
-  size_t start_size_log_2 = MAX2(ceil_log2(table_size), (size_t)2); // 2 is minimum size even though some dictionaries only have one entry
+  size_t start_size_log_2 = MAX2(ceil_log2(table_size), 2); // 2 is minimum size even though some dictionaries only have one entry
   size_t current_size = ((size_t)1) << start_size_log_2;
   log_info(class, loader, data)("Dictionary start size: " SIZE_FORMAT " (" SIZE_FORMAT ")",
                                 current_size, start_size_log_2);
diff --git a/src/hotspot/share/utilities/powerOfTwo.hpp b/src/hotspot/share/utilities/powerOfTwo.hpp
index 786977a347f..6c1e413f403 100644
--- a/src/hotspot/share/utilities/powerOfTwo.hpp
+++ b/src/hotspot/share/utilities/powerOfTwo.hpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -122,10 +122,9 @@ inline T next_power_of_2(T value)  {
 
 // Find log2 value greater than this input
 template <typename T, ENABLE_IF(std::is_integral<T>::value)>
-inline T ceil_log2(T value) {
-  T ret;
-  for (ret = 1; ((T)1 << ret) < value; ++ret);
-  return ret;
+inline int ceil_log2(T value) {
+  assert(value > 0, "Invalid value");
+  return log2i_graceful(value - 1) + 1;
 }
 
 // Return the largest power of two that is a submultiple of the given value.
diff --git a/test/hotspot/gtest/utilities/test_powerOfTwo.cpp b/test/hotspot/gtest/utilities/test_powerOfTwo.cpp
index 4d16e13ab31..fc4080bcefd 100644
--- a/test/hotspot/gtest/utilities/test_powerOfTwo.cpp
+++ b/test/hotspot/gtest/utilities/test_powerOfTwo.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2024, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -305,3 +305,44 @@ TEST(power_of_2, log2i) {
   check_log2i_variants_for((uint)0);
   check_log2i_variants_for((jlong)0);
 }
+
+template <typename T> void test_ceil_log2() {
+  EXPECT_EQ(ceil_log2(T(1)), 0) << "value = " << T(1);
+  EXPECT_EQ(ceil_log2(T(2)), 1) << "value = " << T(2);
+  EXPECT_EQ(ceil_log2(T(3)), 2) << "value = " << T(3);
+  EXPECT_EQ(ceil_log2(T(4)), 2) << "value = " << T(4);
+  EXPECT_EQ(ceil_log2(T(5)), 3) << "value = " << T(5);
+  EXPECT_EQ(ceil_log2(T(6)), 3) << "value = " << T(6);
+  EXPECT_EQ(ceil_log2(T(7)), 3) << "value = " << T(7);
+  EXPECT_EQ(ceil_log2(T(8)), 3) << "value = " << T(8);
+  EXPECT_EQ(ceil_log2(T(9)), 4) << "value = " << T(9);
+  EXPECT_EQ(ceil_log2(T(10)), 4) << "value = " << T(10);
+
+  // Test max values
+  if (std::is_unsigned<T>::value) {
+    EXPECT_EQ(ceil_log2(std::numeric_limits<T>::max()),
+            (int)(sizeof(T) * 8)) << "value = " << std::numeric_limits<T>::max();
+  } else {
+    EXPECT_EQ(ceil_log2(std::numeric_limits<T>::max()),
+            (int)(sizeof(T) * 8 - 1)) << "value = " << std::numeric_limits<T>::max();
+  }
+}
+
+TEST(power_of_2, ceil_log2) {
+  test_ceil_log2<int8_t>();
+  test_ceil_log2<int16_t>();
+  test_ceil_log2<int32_t>();
+  test_ceil_log2<int64_t>();
+  test_ceil_log2<uint8_t>();
+  test_ceil_log2<uint16_t>();
+  test_ceil_log2<uint32_t>();
+  test_ceil_log2<uint64_t>();
+}
+
+#ifdef ASSERT
+TEST_VM_ASSERT_MSG(power_of_2, ceil_log2_invalid,
+    ".*Invalid value") {
+  ceil_log2(0);
+}
+
+#endif // ASSERT