1 files changed, 56 insertions, 0 deletions
diff --git a/extern/draco/dracoenc/src/draco/compression/entropy/shannon_entropy_test.cc b/extern/draco/dracoenc/src/draco/compression/entropy/shannon_entropy_test.cc
new file mode 100644
index 00000000000..c2fe64440be
--- /dev/null
+++ b/extern/draco/dracoenc/src/draco/compression/entropy/shannon_entropy_test.cc
@@ -0,0 +1,56 @@
+#include "draco/compression/entropy/shannon_entropy.h"
+#include "draco/core/draco_test_base.h"
+
+namespace {
+
+TEST(ShannonEntropyTest, TestBinaryEntropy) {
+  // Test verifies that computing binary entropy works as expected.
+  ASSERT_EQ(draco::ComputeBinaryShannonEntropy(0, 0), 0);
+  ASSERT_EQ(draco::ComputeBinaryShannonEntropy(10, 0), 0);
+  ASSERT_EQ(draco::ComputeBinaryShannonEntropy(10, 10), 0);
+  ASSERT_NEAR(draco::ComputeBinaryShannonEntropy(10, 5), 1.0, 1e-4);
+}
+
+TEST(ShannonEntropyTest, TestStreamEntropy) {
+  // Test verifies that the entropy of streamed data is computed correctly.
+  const std::vector<uint32_t> symbols = {1, 5, 1, 100, 2, 1};
+
+  draco::ShannonEntropyTracker entropy_tracker;
+
+  // Nothing added, 0 entropy.
+  ASSERT_EQ(entropy_tracker.GetNumberOfDataBits(), 0);
+
+  // Try to push symbols one by one.
+  uint32_t max_symbol = 0;
+  for (int i = 0; i < symbols.size(); ++i) {
+    if (symbols[i] > max_symbol)
+      max_symbol = symbols[i];
+    const auto entropy_data = entropy_tracker.Push(&symbols[i], 1);
+
+    const int64_t stream_entropy_bits = entropy_tracker.GetNumberOfDataBits();
+    // Ensure the returned entropy_data is in sync with the stream.
+    ASSERT_EQ(draco::ShannonEntropyTracker::GetNumberOfDataBits(entropy_data),
+              stream_entropy_bits);
+
+    // Make sure the entropy is approximately the same as the one we compute
+    // directly from all symbols.
+    const int64_t expected_entropy_bits = draco::ComputeShannonEntropy(
+        symbols.data(), i + 1, max_symbol, nullptr);
+
+    // For now hardcoded tolerance of 2 bits.
+    ASSERT_NEAR(expected_entropy_bits, stream_entropy_bits, 2);
+  }
+
+  // Compare it also to the case when we add all symbols in one call.
+  draco::ShannonEntropyTracker entropy_tracker_2;
+  entropy_tracker_2.Push(symbols.data(), symbols.size());
+  const int64_t stream_2_entropy_bits = entropy_tracker_2.GetNumberOfDataBits();
+  ASSERT_EQ(entropy_tracker.GetNumberOfDataBits(), stream_2_entropy_bits);
+
+  // Ensure that peeking does not change the entropy.
+  entropy_tracker_2.Peek(symbols.data(), 1);
+
+  ASSERT_EQ(stream_2_entropy_bits, entropy_tracker_2.GetNumberOfDataBits());
+}
+
+}  // namespace