diff --git a/libc/test/src/__support/FPUtil/fpbits_test.cpp b/libc/test/src/__support/FPUtil/fpbits_test.cpp
diff --git a/libc/test/src/__support/integer_literals_test.cpp b/libc/test/src/__support/integer_literals_test.cpp
@@ -0,0 +1,134 @@
+
+//===-- Unittests for user defined integer literals -----------------------===//
+//
+// 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/integer_literals.h"
+#include "test/UnitTest/Test.h"
+
+using LIBC_NAMESPACE::operator""_u8;
+using LIBC_NAMESPACE::operator""_u16;
+using LIBC_NAMESPACE::operator""_u32;
+using LIBC_NAMESPACE::operator""_u64;
+using LIBC_NAMESPACE::operator""_u128;
+using LIBC_NAMESPACE::operator""_u256;
+
+TEST(LlvmLibcIntegerLiteralTest, u8) {
+  EXPECT_EQ(uint8_t(0), 0_u8);
+  EXPECT_EQ(uint8_t(UINT8_MAX), 255_u8);
+  EXPECT_EQ(uint8_t(UINT8_MAX), 0xFF_u8);
+  EXPECT_EQ(uint8_t(UINT8_MAX), 0b11111111_u8);
+}
+
+TEST(LlvmLibcIntegerLiteralTest, u16) {
+  EXPECT_EQ(uint16_t(0), 0_u16);
+  EXPECT_EQ(uint16_t(UINT8_MAX), 255_u16);
+  EXPECT_EQ(uint16_t(UINT8_MAX), 0xFF_u16);
+  EXPECT_EQ(uint16_t(UINT8_MAX), 0b11111111_u16);
+  EXPECT_EQ(uint16_t(UINT16_MAX), 65535_u16);
+  EXPECT_EQ(uint16_t(UINT16_MAX), 0xFFFF_u16);
+  EXPECT_EQ(uint16_t(UINT16_MAX), 0b11111111'11111111_u16);
+}
+
+TEST(LlvmLibcIntegerLiteralTest, u32) {
+  EXPECT_EQ(uint32_t(0), 0_u32);
+  EXPECT_EQ(uint32_t(UINT8_MAX), 255_u32);
+  EXPECT_EQ(uint32_t(UINT8_MAX), 0xFF_u32);
+  EXPECT_EQ(uint32_t(UINT8_MAX), 0b11111111_u32);
+  EXPECT_EQ(uint32_t(UINT16_MAX), 65535_u32);
+  EXPECT_EQ(uint32_t(UINT16_MAX), 0xFFFF_u32);
+  EXPECT_EQ(uint32_t(UINT16_MAX), 0b11111111'11111111_u32);
+  EXPECT_EQ(uint32_t(UINT32_MAX), 4294967295_u32);
+  EXPECT_EQ(uint32_t(UINT32_MAX), 0xFFFFFFFF_u32);
+  EXPECT_EQ(uint32_t(UINT32_MAX), 0b1111111111111111'1111111111111111_u32);
+}
+
+TEST(LlvmLibcIntegerLiteralTest, u64) {
+  EXPECT_EQ(uint64_t(0), 0_u64);
+  EXPECT_EQ(uint64_t(UINT8_MAX), 255_u64);
+  EXPECT_EQ(uint64_t(UINT8_MAX), 0xFF_u64);
+  EXPECT_EQ(uint64_t(UINT8_MAX), 0b11111111_u64);
+  EXPECT_EQ(uint64_t(UINT16_MAX), 65535_u64);
+  EXPECT_EQ(uint64_t(UINT16_MAX), 0xFFFF_u64);
+  EXPECT_EQ(uint64_t(UINT16_MAX), 0b11111111'11111111_u64);
+  EXPECT_EQ(uint64_t(UINT32_MAX), 4294967295_u64);
+  EXPECT_EQ(uint64_t(UINT32_MAX), 0xFFFFFFFF_u64);
+  EXPECT_EQ(uint64_t(UINT32_MAX), 0b1111111111111111'1111111111111111_u64);
+  EXPECT_EQ(uint64_t(UINT64_MAX), 18446744073709551615_u64);
+  EXPECT_EQ(uint64_t(UINT64_MAX), 0xFFFFFFFF'FFFFFFFF_u64);
+  EXPECT_EQ(
+      uint64_t(UINT64_MAX),
+      0b1111111111111111'1111111111111111'1111111111111111'1111111111111111_u64);
+}
+
+TEST(LlvmLibcIntegerLiteralTest, u128) {
+#if defined(__SIZEOF_INT128__)
+  const __uint128_t ZERO = 0;
+  const __uint128_t U8_MAX = UINT8_MAX;
+  const __uint128_t U16_MAX = UINT16_MAX;
+  const __uint128_t U32_MAX = UINT32_MAX;
+  const __uint128_t U64_MAX = UINT64_MAX;
+  const __uint128_t U128_MAX = (U64_MAX << 64) | U64_MAX;
+#else
+  const UInt128 ZERO = 0;
+  const UInt128 U8_MAX = UINT8_MAX;
+  const UInt128 U16_MAX = UINT16_MAX;
+  const UInt128 U32_MAX = UINT32_MAX;
+  const UInt128 U64_MAX = UINT64_MAX;
+  const UInt128 U128_MAX = (U64_MAX << 64) | U64_MAX;
+#endif
+  EXPECT_EQ(ZERO, 0_u128);
+  EXPECT_EQ(U8_MAX, 255_u128);
+  EXPECT_EQ(U8_MAX, 0xFF_u128);
+  EXPECT_EQ(U8_MAX, 0b11111111_u128);
+  EXPECT_EQ(U16_MAX, 65535_u128);
+  EXPECT_EQ(U16_MAX, 0xFFFF_u128);
+  EXPECT_EQ(U16_MAX, 0b11111111'11111111_u128);
+  EXPECT_EQ(U32_MAX, 4294967295_u128);
+  EXPECT_EQ(U32_MAX, 0xFFFFFFFF_u128);
+  EXPECT_EQ(U32_MAX, 0b1111111111111111'1111111111111111_u128);
+  EXPECT_EQ(U64_MAX, 18446744073709551615_u128);
+  EXPECT_EQ(U64_MAX, 0xFFFFFFFF'FFFFFFFF_u128);
+  EXPECT_EQ(
+      U64_MAX,
+      0b1111111111111111'1111111111111111'1111111111111111'1111111111111111_u128);
+  EXPECT_EQ(U128_MAX, 340282366920938463463374607431768211455_u128);
+  EXPECT_EQ(U128_MAX, 0xFFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF_u128);
+  EXPECT_EQ(
+      U128_MAX,
+      0b1111111111111111'1111111111111111'1111111111111111'1111111111111111'1111111111111111'1111111111111111'1111111111111111'1111111111111111_u128);
+}
+
+TEST(LlvmLibcIntegerLiteralTest, u256) {
+  using UInt256 = LIBC_NAMESPACE::cpp::UInt<256>;
+  const UInt256 ZERO = 0;
+  const UInt256 U8_MAX = UINT8_MAX;
+  const UInt256 U16_MAX = UINT16_MAX;
+  const UInt256 U32_MAX = UINT32_MAX;
+  const UInt256 U64_MAX = UINT64_MAX;
+  const UInt256 U128_MAX = (U64_MAX << 64) | U64_MAX;
+  const UInt256 U256_MAX = (U128_MAX << 128) | U128_MAX;
+  EXPECT_EQ(ZERO, 0_u256);
+  EXPECT_EQ(U8_MAX, 255_u256);
+  EXPECT_EQ(U8_MAX, 0xFF_u256);
+  EXPECT_EQ(U8_MAX, 0b11111111_u256);
+  EXPECT_EQ(U16_MAX, 65535_u256);
+  EXPECT_EQ(U16_MAX, 0xFFFF_u256);
+  EXPECT_EQ(U16_MAX, 0b11111111'11111111_u256);
+  EXPECT_EQ(U32_MAX, 4294967295_u256);
+  EXPECT_EQ(U32_MAX, 0xFFFFFFFF_u256);
+  EXPECT_EQ(U32_MAX, 0b1111111111111111'1111111111111111_u256);
+  EXPECT_EQ(U64_MAX, 18446744073709551615_u256);
+  EXPECT_EQ(U64_MAX, 0xFFFFFFFF'FFFFFFFF_u256);
+  EXPECT_EQ(
+      U64_MAX,
+      0b1111111111111111'1111111111111111'1111111111111111'1111111111111111_u256);
+  EXPECT_EQ(U128_MAX, 0xFFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF_u256);
+  EXPECT_EQ(
+      U256_MAX,
+      0xFFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF'FFFFFFFF_u256);
+}
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -472,6 +472,15 @@ libc_support_library(
     ],
 )
 
+libc_support_library(
+    name = "__support_integer_literals",
+    hdrs = ["src/__support/integer_literals.h"],
+    deps = [
+        ":__support_cpp_limits",
+        ":__support_uint128",
+    ],
+)
+
 libc_support_library(
     name = "__support_str_to_num_result",
     hdrs = ["src/__support/str_to_num_result.h"],

diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/__support/BUILD.bazel
@@ -99,3 +99,11 @@ libc_test(
         "//libc:__support_char_vector",
     ],
 )
+
+libc_test(
+    name = "integer_literals_test",
+    srcs = ["integer_literals_test.cpp"],
+    deps = [
+        "//libc:__support_integer_literals",
+    ],
+)
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/__support/FPUtil/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/__support/FPUtil/BUILD.bazel
@@ -16,6 +16,7 @@ libc_test(
     deps = [
         "//libc:__support_fputil_fp_bits",
         "//libc:__support_fputil_fpbits_str",
+        "//libc:__support_integer_literals",
     ],
 )