Export of internal Abseil changes

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8e04df6fcbd062e5eaf179a6ec9b0a26f8aa8a39 by Abseil Team <absl-team@google.com>:

Use a floating point type for the example usage of absl::uniform_real_distribution.

PiperOrigin-RevId: 271167776

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5f8f1dfea50bc16a9d9af3e50c4636500a938b29 by Abseil Team <absl-team@google.com>:

the llvm wasm backend does not support this data symbol in text section, so remove it from the test.

PiperOrigin-RevId: 271138100

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2874542cb212962ac3093fd78fd5e1eb85c126c0 by Xiaoyi Zhang <zhangxy@google.com>:

Work around MSVC 2019 compiler bug related to constexpr in optional_test.
The change in optional_test is necessary to avoid another bug on MSVC
complaining about accessing invalid member of union, and also makes the test
more reasonale by checking the value of a non-static member.

Filed a bug against MSVC
https://developercommunity.visualstudio.com/content/problem/743998/internal-compiler-error-related-to-constexpr-and-u.html.

PiperOrigin-RevId: 271129805

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3a5d56f0c3362aabf68938fb95c4e2d3eca59538 by Abseil Team <absl-team@google.com>:

Improve precision of absl::GetCurrentTimeNanos() by adjusting
cycle time sooner.

PiperOrigin-RevId: 271007945

--
1e044a6dec7c0ca150fff1aee52dbdb16aa43ed7 by Abseil Team <absl-team@google.com>:

Internal change.

PiperOrigin-RevId: 270962690
GitOrigin-RevId: 8e04df6fcbd062e5eaf179a6ec9b0a26f8aa8a39
Change-Id: Icb05423a7e93ebdae16baadd59a60b75b5cfa249

2 files changed, 12 insertions, 4 deletions

diff --git a/absl/container/btree_test.cc b/absl/container/btree_test.cc
index 4edb277..48f70cb 100644
--- a/absl/container/btree_test.cc
+++ b/absl/container/btree_test.cc
@@ -2239,6 +2239,13 @@ TEST(Btree, MoveAssignmentAllocatorPropagation) {
   }
 }
 
+TEST(Btree, EmptyTree) {
+  absl::btree_set<int> s;
+  EXPECT_TRUE(s.empty());
+  EXPECT_EQ(s.size(), 0);
+  EXPECT_GT(s.max_size(), 0);
+}
+
 }  // namespace
 }  // namespace container_internal
 }  // namespace absl
diff --git a/absl/container/internal/btree.h b/absl/container/internal/btree.h
index b255984..cf7ef02 100644
--- a/absl/container/internal/btree.h
+++ b/absl/container/internal/btree.h
@@ -1226,7 +1226,7 @@ class btree {
   // The height of the btree. An empty tree will have height 0.
   size_type height() const {
     size_type h = 0;
-    if (root()) {
+    if (!empty()) {
       // Count the length of the chain from the leftmost node up to the
       // root. We actually count from the root back around to the level below
       // the root, but the calculation is the same because of the circularity
@@ -1277,16 +1277,17 @@ class btree {
   // divided by the maximum number of elements a tree with the current number
   // of nodes could hold. A value of 1 indicates perfect space
   // utilization. Smaller values indicate space wastage.
+  // Returns 0 for empty trees.
   double fullness() const {
+    if (empty()) return 0.0;
     return static_cast<double>(size()) / (nodes() * kNodeValues);
   }
   // The overhead of the btree structure in bytes per node. Computed as the
   // total number of bytes used by the btree minus the number of bytes used for
   // storing elements divided by the number of elements.
+  // Returns 0 for empty trees.
   double overhead() const {
-    if (empty()) {
-      return 0.0;
-    }
+    if (empty()) return 0.0;
     return (bytes_used() - size() * sizeof(value_type)) /
            static_cast<double>(size());
   }