diff --git a/libc/test/src/stdbit/stdc_bit_floor_ul_test.cpp b/libc/test/src/stdbit/stdc_bit_floor_ul_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_bit_floor_ul -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_bit_floor_ul.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcBitfloorUlTest, Zero) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_ul(0UL), 0UL);
+}
+
+TEST(LlvmLibcStdcBitfloorUlTest, Ones) {
+  for (unsigned i = 0U; i != ULONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_ul(ULONG_MAX >> i),
+              1UL << (ULONG_WIDTH - i - 1));
+}
diff --git a/libc/test/src/stdbit/stdc_bit_floor_ull_test.cpp b/libc/test/src/stdbit/stdc_bit_floor_ull_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_bit_floor_ull ----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_bit_floor_ull.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcBitfloorUllTest, Zero) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_ull(0ULL), 0ULL);
+}
+
+TEST(LlvmLibcStdcBitfloorUllTest, Ones) {
+  for (unsigned i = 0U; i != ULLONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_ull(ULLONG_MAX >> i),
+              1ULL << (ULLONG_WIDTH - i - 1));
+}
diff --git a/libc/test/src/stdbit/stdc_bit_floor_us_test.cpp b/libc/test/src/stdbit/stdc_bit_floor_us_test.cpp
@@ -0,0 +1,22 @@
+//===-- Unittests for stdc_bit_floor_us -----------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_bit_floor_us.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcBitfloorUsTest, Zero) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_us(0U),
+            static_cast<unsigned short>(0));
+}
+
+TEST(LlvmLibcStdcBitfloorUsTest, Ones) {
+  for (unsigned i = 0U; i != USHRT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_bit_floor_us(USHRT_MAX >> i),
+              static_cast<unsigned short>(1 << (USHRT_WIDTH - i - 1)));
+}