--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/gtest/runtime/test_os.cpp	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2016, 2017, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "precompiled.hpp"
+#include "runtime/os.hpp"
+#include "unittest.hpp"
+
+static size_t small_page_size() {
+  return os::vm_page_size();
+}
+
+static size_t large_page_size() {
+  const size_t large_page_size_example = 4 * M;
+  return os::page_size_for_region_aligned(large_page_size_example, 1);
+}
+
+TEST_VM(os, page_size_for_region) {
+  size_t large_page_example = 4 * M;
+  size_t large_page = os::page_size_for_region_aligned(large_page_example, 1);
+
+  size_t small_page = os::vm_page_size();
+  if (large_page > small_page) {
+    size_t num_small_in_large = large_page / small_page;
+    size_t page = os::page_size_for_region_aligned(large_page, num_small_in_large);
+    ASSERT_EQ(page, small_page) << "Did not get a small page";
+  }
+}
+
+TEST_VM(os, page_size_for_region_aligned) {
+  if (UseLargePages) {
+    const size_t small_page = small_page_size();
+    const size_t large_page = large_page_size();
+
+    if (large_page > small_page) {
+      size_t num_small_pages_in_large = large_page / small_page;
+      size_t page = os::page_size_for_region_aligned(large_page, num_small_pages_in_large);
+
+      ASSERT_EQ(page, small_page);
+    }
+  }
+}
+
+TEST_VM(os, page_size_for_region_alignment) {
+  if (UseLargePages) {
+    const size_t small_page = small_page_size();
+    const size_t large_page = large_page_size();
+    if (large_page > small_page) {
+      const size_t unaligned_region = large_page + 17;
+      size_t page = os::page_size_for_region_aligned(unaligned_region, 1);
+      ASSERT_EQ(page, small_page);
+
+      const size_t num_pages = 5;
+      const size_t aligned_region = large_page * num_pages;
+      page = os::page_size_for_region_aligned(aligned_region, num_pages);
+      ASSERT_EQ(page, large_page);
+    }
+  }
+}
+
+TEST_VM(os, page_size_for_region_unaligned) {
+  if (UseLargePages) {
+    // Given exact page size, should return that page size.
+    for (size_t i = 0; os::_page_sizes[i] != 0; i++) {
+      size_t expected = os::_page_sizes[i];
+      size_t actual = os::page_size_for_region_unaligned(expected, 1);
+      ASSERT_EQ(expected, actual);
+    }
+
+    // Given slightly larger size than a page size, return the page size.
+    for (size_t i = 0; os::_page_sizes[i] != 0; i++) {
+      size_t expected = os::_page_sizes[i];
+      size_t actual = os::page_size_for_region_unaligned(expected + 17, 1);
+      ASSERT_EQ(expected, actual);
+    }
+
+    // Given a slightly smaller size than a page size,
+    // return the next smaller page size.
+    if (os::_page_sizes[1] > os::_page_sizes[0]) {
+      size_t expected = os::_page_sizes[0];
+      size_t actual = os::page_size_for_region_unaligned(os::_page_sizes[1] - 17, 1);
+      ASSERT_EQ(actual, expected);
+    }
+
+    // Return small page size for values less than a small page.
+    size_t small_page = small_page_size();
+    size_t actual = os::page_size_for_region_unaligned(small_page - 17, 1);
+    ASSERT_EQ(small_page, actual);
+  }
+}
+
+TEST(os, test_random) {
+  const double m = 2147483647;
+  double mean = 0.0, variance = 0.0, t;
+  const int reps = 10000;
+  unsigned int seed = 1;
+
+  // tty->print_cr("seed %ld for %ld repeats...", seed, reps);
+  os::init_random(seed);
+  int num;
+  for (int k = 0; k < reps; k++) {
+    num = os::random();
+    double u = (double)num / m;
+    ASSERT_TRUE(u >= 0.0 && u <= 1.0) << "bad random number!";
+
+    // calculate mean and variance of the random sequence
+    mean += u;
+    variance += (u*u);
+  }
+  mean /= reps;
+  variance /= (reps - 1);
+
+  ASSERT_EQ(num, 1043618065) << "bad seed";
+  // tty->print_cr("mean of the 1st 10000 numbers: %f", mean);
+  int intmean = mean*100;
+  ASSERT_EQ(intmean, 50);
+  // tty->print_cr("variance of the 1st 10000 numbers: %f", variance);
+  int intvariance = variance*100;
+  ASSERT_EQ(intvariance, 33);
+  const double eps = 0.0001;
+  t = fabsd(mean - 0.5018);
+  ASSERT_LT(t, eps) << "bad mean";
+  t = (variance - 0.3355) < 0.0 ? -(variance - 0.3355) : variance - 0.3355;
+  ASSERT_LT(t, eps) << "bad variance";
+}
+
+
+#ifdef ASSERT
+TEST_VM_ASSERT_MSG(os, page_size_for_region_with_zero_min_pages, "sanity") {
+  size_t region_size = 16 * os::vm_page_size();
+  os::page_size_for_region_aligned(region_size, 0); // should assert
+}
+#endif