diff --git a/libs/ftl/Android.bp b/libs/ftl/Android.bp
index 97626be..2226791 100644
--- a/libs/ftl/Android.bp
+++ b/libs/ftl/Android.bp
@@ -14,6 +14,7 @@
         address: true,
     },
     srcs: [
+        "cast_test.cpp",
         "future_test.cpp",
         "small_map_test.cpp",
         "small_vector_test.cpp",
diff --git a/libs/ftl/cast_test.cpp b/libs/ftl/cast_test.cpp
new file mode 100644
index 0000000..2abcb8f
--- /dev/null
+++ b/libs/ftl/cast_test.cpp
@@ -0,0 +1,200 @@
+/*
+ * Copyright 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <ftl/cast.h>
+#include <gtest/gtest.h>
+
+#include <cfloat>
+#include <cmath>
+#include <limits>
+
+namespace android::test {
+
+using ftl::cast_safety;
+using ftl::CastSafety;
+
+template <typename T>
+constexpr T min = std::numeric_limits<T>::lowest();
+
+template <typename T>
+constexpr T max = std::numeric_limits<T>::max();
+
+template <typename T>
+constexpr T inf = std::numeric_limits<T>::infinity();
+
+template <typename T>
+constexpr T NaN = std::numeric_limits<T>::quiet_NaN();
+
+// Keep in sync with example usage in header file.
+
+static_assert(cast_safety<uint8_t>(-1) == CastSafety::kUnderflow);
+static_assert(cast_safety<int8_t>(128u) == CastSafety::kOverflow);
+
+static_assert(cast_safety<uint32_t>(-.1f) == CastSafety::kUnderflow);
+static_assert(cast_safety<int32_t>(static_cast<float>(INT32_MAX)) == CastSafety::kOverflow);
+
+static_assert(cast_safety<float>(-DBL_MAX) == CastSafety::kUnderflow);
+
+// Unsigned to unsigned.
+
+static_assert(cast_safety<uint8_t>(0u) == CastSafety::kSafe);
+static_assert(cast_safety<uint16_t>(max<uint8_t>) == CastSafety::kSafe);
+static_assert(cast_safety<uint8_t>(static_cast<uint32_t>(max<uint8_t>)) == CastSafety::kSafe);
+
+static_assert(cast_safety<uint32_t>(max<uint64_t>) == CastSafety::kOverflow);
+static_assert(cast_safety<uint8_t>(static_cast<uint32_t>(max<uint8_t>) + 1) ==
+              CastSafety::kOverflow);
+
+// Unsigned to signed.
+
+static_assert(cast_safety<int16_t>(0u) == CastSafety::kSafe);
+static_assert(cast_safety<int16_t>(max<uint8_t>) == CastSafety::kSafe);
+static_assert(cast_safety<int16_t>(max<uint16_t>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<int64_t>(static_cast<uint64_t>(max<int64_t>) - 1) == CastSafety::kSafe);
+static_assert(cast_safety<int64_t>(static_cast<uint64_t>(max<int64_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int64_t>(static_cast<uint64_t>(max<int64_t>) + 1) ==
+              CastSafety::kOverflow);
+
+// Signed to unsigned.
+
+static_assert(cast_safety<uint16_t>(0) == CastSafety::kSafe);
+static_assert(cast_safety<uint16_t>(max<int8_t>) == CastSafety::kSafe);
+static_assert(cast_safety<uint16_t>(max<int16_t>) == CastSafety::kSafe);
+
+static_assert(cast_safety<uint32_t>(-1) == CastSafety::kUnderflow);
+static_assert(cast_safety<uint32_t>(max<int64_t>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<uint32_t>(static_cast<int64_t>(max<uint32_t>) - 1) == CastSafety::kSafe);
+static_assert(cast_safety<uint32_t>(static_cast<int64_t>(max<uint32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<uint32_t>(static_cast<int64_t>(max<uint32_t>) + 1) ==
+              CastSafety::kOverflow);
+
+// Signed to signed.
+
+static_assert(cast_safety<int8_t>(-129) == CastSafety::kUnderflow);
+static_assert(cast_safety<int8_t>(-128) == CastSafety::kSafe);
+static_assert(cast_safety<int8_t>(127) == CastSafety::kSafe);
+static_assert(cast_safety<int8_t>(128) == CastSafety::kOverflow);
+
+static_assert(cast_safety<int32_t>(static_cast<int64_t>(min<int32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int32_t>(static_cast<int64_t>(max<int32_t>)) == CastSafety::kSafe);
+
+static_assert(cast_safety<int16_t>(min<int32_t>) == CastSafety::kUnderflow);
+static_assert(cast_safety<int32_t>(max<int64_t>) == CastSafety::kOverflow);
+
+// Float to float.
+
+static_assert(cast_safety<double>(max<float>) == CastSafety::kSafe);
+static_assert(cast_safety<double>(min<float>) == CastSafety::kSafe);
+
+static_assert(cast_safety<float>(min<double>) == CastSafety::kUnderflow);
+static_assert(cast_safety<float>(max<double>) == CastSafety::kOverflow);
+
+TEST(CastSafety, FloatToFloat) {
+  EXPECT_EQ(cast_safety<float>(std::nexttoward(static_cast<double>(min<float>), min<double>)),
+            CastSafety::kUnderflow);
+  EXPECT_EQ(cast_safety<float>(std::nexttoward(static_cast<double>(max<float>), max<double>)),
+            CastSafety::kOverflow);
+}
+
+// Unsigned to float.
+
+static_assert(cast_safety<float>(0u) == CastSafety::kSafe);
+static_assert(cast_safety<float>(max<uint64_t>) == CastSafety::kSafe);
+
+static_assert(cast_safety<double>(0u) == CastSafety::kSafe);
+static_assert(cast_safety<double>(max<uint64_t>) == CastSafety::kSafe);
+
+// Signed to float.
+
+static_assert(cast_safety<float>(min<int64_t>) == CastSafety::kSafe);
+static_assert(cast_safety<float>(max<int64_t>) == CastSafety::kSafe);
+
+static_assert(cast_safety<double>(min<int64_t>) == CastSafety::kSafe);
+static_assert(cast_safety<double>(max<int64_t>) == CastSafety::kSafe);
+
+// Float to unsigned.
+
+static_assert(cast_safety<uint32_t>(0.f) == CastSafety::kSafe);
+static_assert(cast_safety<uint32_t>(min<float>) == CastSafety::kUnderflow);
+static_assert(cast_safety<uint32_t>(max<float>) == CastSafety::kOverflow);
+static_assert(cast_safety<uint32_t>(-.1f) == CastSafety::kUnderflow);
+
+static_assert(cast_safety<uint16_t>(-inf<float>) == CastSafety::kUnderflow);
+static_assert(cast_safety<uint32_t>(inf<float>) == CastSafety::kOverflow);
+static_assert(cast_safety<uint64_t>(NaN<float>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<uint32_t>(static_cast<float>(max<int32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<uint32_t>(static_cast<float>(max<uint32_t>)) == CastSafety::kOverflow);
+static_assert(cast_safety<uint32_t>(static_cast<double>(max<int32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<uint32_t>(static_cast<double>(max<uint32_t>)) == CastSafety::kSafe);
+
+static_assert(cast_safety<uint64_t>(0.0) == CastSafety::kSafe);
+static_assert(cast_safety<uint64_t>(min<double>) == CastSafety::kUnderflow);
+static_assert(cast_safety<uint64_t>(max<double>) == CastSafety::kOverflow);
+static_assert(cast_safety<uint64_t>(-.1) == CastSafety::kUnderflow);
+
+static_assert(cast_safety<uint64_t>(static_cast<float>(max<int64_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<uint64_t>(static_cast<float>(max<uint64_t>)) == CastSafety::kOverflow);
+static_assert(cast_safety<uint64_t>(static_cast<double>(max<int64_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<uint64_t>(static_cast<double>(max<uint64_t>)) == CastSafety::kOverflow);
+
+// Float to signed.
+
+static_assert(cast_safety<int32_t>(0.f) == CastSafety::kSafe);
+static_assert(cast_safety<int32_t>(min<float>) == CastSafety::kUnderflow);
+static_assert(cast_safety<int32_t>(max<float>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<int16_t>(-inf<double>) == CastSafety::kUnderflow);
+static_assert(cast_safety<int32_t>(inf<double>) == CastSafety::kOverflow);
+static_assert(cast_safety<int64_t>(NaN<double>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<int32_t>(static_cast<float>(min<int32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int32_t>(static_cast<float>(max<int32_t>)) == CastSafety::kOverflow);
+static_assert(cast_safety<int32_t>(static_cast<double>(min<int32_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int32_t>(static_cast<double>(max<int32_t>)) == CastSafety::kSafe);
+
+static_assert(cast_safety<int64_t>(0.0) == CastSafety::kSafe);
+static_assert(cast_safety<int64_t>(min<double>) == CastSafety::kUnderflow);
+static_assert(cast_safety<int64_t>(max<double>) == CastSafety::kOverflow);
+
+static_assert(cast_safety<int64_t>(static_cast<float>(min<int64_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int64_t>(static_cast<float>(max<int64_t>)) == CastSafety::kOverflow);
+static_assert(cast_safety<int64_t>(static_cast<double>(min<int64_t>)) == CastSafety::kSafe);
+static_assert(cast_safety<int64_t>(static_cast<double>(max<int64_t>)) == CastSafety::kOverflow);
+
+TEST(CastSafety, FloatToSigned) {
+  constexpr int32_t kMax = ftl::details::safe_limits<int32_t, float>::max();
+  static_assert(kMax == 2'147'483'520);
+  EXPECT_EQ(kMax, static_cast<int32_t>(std::nexttowardf(max<int32_t>, 0)));
+
+  EXPECT_EQ(cast_safety<int32_t>(std::nexttowardf(min<int32_t>, 0)), CastSafety::kSafe);
+  EXPECT_EQ(cast_safety<int32_t>(std::nexttowardf(max<int32_t>, 0)), CastSafety::kSafe);
+  EXPECT_EQ(cast_safety<int64_t>(std::nexttoward(min<int64_t>, 0)), CastSafety::kSafe);
+  EXPECT_EQ(cast_safety<int64_t>(std::nexttoward(max<int64_t>, 0)), CastSafety::kSafe);
+
+  EXPECT_EQ(cast_safety<int32_t>(std::nexttowardf(min<int32_t>, min<float>)),
+            CastSafety::kUnderflow);
+  EXPECT_EQ(cast_safety<int32_t>(std::nexttowardf(max<int32_t>, max<float>)),
+            CastSafety::kOverflow);
+  EXPECT_EQ(cast_safety<int64_t>(std::nexttoward(min<int64_t>, min<double>)),
+            CastSafety::kUnderflow);
+  EXPECT_EQ(cast_safety<int64_t>(std::nexttoward(max<int64_t>, max<double>)),
+            CastSafety::kOverflow);
+}
+
+}  // namespace android::test