[libc][math] Implement nan(f|l) functions (#76690)

Specification: https://en.cppreference.com/w/c/numeric/math/nan

libc/config/darwin/arm/entrypoints.txt

@@ -193,6 +193,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl
+    libc.src.math.nan
+    libc.src.math.nanf
+    libc.src.math.nanl
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nearbyintl

libc/config/darwin/x86_64/entrypoints.txt

@@ -172,6 +172,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     #libc.src.math.modf
     #libc.src.math.modff
     #libc.src.math.modfl
+    #libc.src.math.nan
+    #libc.src.math.nanf
+    #libc.src.math.nanl
     #libc.src.math.nearbyint
     #libc.src.math.nearbyintf
     #libc.src.math.nearbyintl

libc/config/gpu/entrypoints.txt

@@ -215,6 +215,8 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.lroundf
     libc.src.math.modf
     libc.src.math.modff
+    libc.src.math.nan
+    libc.src.math.nanf
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nextafter

libc/config/linux/aarch64/entrypoints.txt

@@ -313,6 +313,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl
+    libc.src.math.nan
+    libc.src.math.nanf
+    libc.src.math.nanl
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nearbyintl

libc/config/linux/riscv/entrypoints.txt

@@ -322,6 +322,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl
+    libc.src.math.nan
+    libc.src.math.nanf
+    libc.src.math.nanl
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nearbyintl

libc/config/linux/x86_64/entrypoints.txt

@@ -323,6 +323,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl
+    libc.src.math.nan
+    libc.src.math.nanf
+    libc.src.math.nanl
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nearbyintl

libc/config/windows/entrypoints.txt

@@ -192,6 +192,9 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.modf
     libc.src.math.modff
     libc.src.math.modfl
+    libc.src.math.nan
+    libc.src.math.nanf
+    libc.src.math.nanl
     libc.src.math.nearbyint
     libc.src.math.nearbyintf
     libc.src.math.nearbyintl

libc/docs/math/index.rst

@@ -212,11 +212,11 @@ Basic Operations
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | modfl        | |check| | |check| |         | |check| | |check| |         |         | |check| |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| nan          |         |         |         |         |         |         |         |         |         |         |         |         |
+| nan          | |check| | |check| |         | |check| | |check| |         |         | |check| |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| nanf         |         |         |         |         |         |         |         |         |         |         |         |         |
+| nanf         | |check| | |check| |         | |check| | |check| |         |         | |check| |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
-| nanl         |         |         |         |         |         |         |         |         |         |         |         |         |
+| nanl         | |check| | |check| |         | |check| | |check| |         |         | |check| |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+
 | nearbyint    | |check| | |check| |         | |check| | |check| |         |         | |check| |         |         |         |         |
 +--------------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+---------+

libc/spec/stdc.td

@@ -515,6 +515,10 @@ def StdC : StandardSpec<"stdc"> {
           FunctionSpec<"scalbn", RetValSpec<DoubleType>, [ArgSpec<DoubleType>, ArgSpec<IntType>]>,
           FunctionSpec<"scalbnf", RetValSpec<FloatType>, [ArgSpec<FloatType>, ArgSpec<IntType>]>,
           FunctionSpec<"scalbnl", RetValSpec<LongDoubleType>, [ArgSpec<LongDoubleType>, ArgSpec<IntType>]>,
+
+          FunctionSpec<"nanf", RetValSpec<FloatType>, [ArgSpec<ConstCharPtr>]>,
+          FunctionSpec<"nan", RetValSpec<DoubleType>, [ArgSpec<ConstCharPtr>]>,
+          FunctionSpec<"nanl", RetValSpec<LongDoubleType>, [ArgSpec<ConstCharPtr>]>,
       ]
   >;
 

libc/src/__support/str_to_float.h

@@ -12,6 +12,7 @@
 #include "src/__support/CPP/bit.h"
 #include "src/__support/CPP/limits.h"
 #include "src/__support/CPP/optional.h"
+#include "src/__support/CPP/string_view.h"
 #include "src/__support/FPUtil/FEnvImpl.h"
 #include "src/__support/FPUtil/FPBits.h"
 #include "src/__support/FPUtil/dyadic_float.h"
@@ -1044,6 +1045,27 @@ hexadecimal_string_to_float(const char *__restrict src,
   return output;
 }
 
+LIBC_INLINE uint64_t
+nan_mantissa_from_ncharseq(const cpp::string_view ncharseq) {
+  uint64_t nan_mantissa = 0;
+
+  if (ncharseq.data() != nullptr && isdigit(ncharseq[0])) {
+    // This is to prevent errors when StorageType is larger than 64
+    // bits, since strtointeger only supports up to 64 bits. This is
+    // actually more than is required by the specification, which says
+    // for the input type "NAN(n-char-sequence)" that "the meaning of
+    // the n-char sequence is implementation-defined."
+    auto strtoint_result = strtointeger<uint64_t>(ncharseq.data(), 0);
+    if (!strtoint_result.has_error())
+      nan_mantissa = strtoint_result.value;
+
+    if (strtoint_result.parsed_len != static_cast<ptrdiff_t>(ncharseq.size()))
+      nan_mantissa = 0;
+  }
+
+  return nan_mantissa;
+}
+
 // Takes a pointer to a string and a pointer to a string pointer. This function
 // is used as the backend for all of the string to float functions.
 template <class T>
@@ -1136,31 +1158,18 @@ LIBC_INLINE StrToNumResult<T> strtofloatingpoint(const char *__restrict src) {
           ++index;
         if (src[index] == ')') {
           ++index;
-          if (isdigit(src[left_paren + 1])) {
-            // This is to prevent errors when StorageType is larger than 64
-            // bits, since strtointeger only supports up to 64 bits. This is
-            // actually more than is required by the specification, which says
-            // for the input type "NAN(n-char-sequence)" that "the meaning of
-            // the n-char sequence is implementation-defined."
-
-            auto strtoint_result =
-                strtointeger<uint64_t>(src + (left_paren + 1), 0);
-            if (strtoint_result.has_error()) {
-              error = strtoint_result.error;
-            }
-            nan_mantissa = static_cast<StorageType>(strtoint_result.value);
-            if (src[left_paren + 1 + strtoint_result.parsed_len] != ')')
-              nan_mantissa = 0;
-          }
+          auto nan_mantissa_result = nan_mantissa_from_ncharseq(
+              cpp::string_view(src + (left_paren + 1), index - left_paren - 2));
+          nan_mantissa = static_cast<StorageType>(nan_mantissa_result);
         } else {
           index = left_paren;
         }
       }
+
       if (result.get_sign()) {
         result = FPBits(result.build_quiet_nan(nan_mantissa));
         result.set_sign(true);
       } else {
-        result.set_sign(false);
         result = FPBits(result.build_quiet_nan(nan_mantissa));
       }
     }
@@ -1195,6 +1204,28 @@ LIBC_INLINE StrToNumResult<T> strtofloatingpoint(const char *__restrict src) {
   return {T(result), index, error};
 }
 
+template <class T> LIBC_INLINE StrToNumResult<T> strtonan(const char *arg) {
+  using FPBits = typename fputil::FPBits<T>;
+  using StorageType = typename FPBits::StorageType;
+
+  FPBits result;
+  int error = 0;
+  StorageType nan_mantissa = 0;
+
+  ptrdiff_t index = 0;
+  while (isalnum(arg[index]) || arg[index] == '_')
+    ++index;
+
+  if (arg[index] == '\0') {
+    auto nan_mantissa_result =
+        nan_mantissa_from_ncharseq(cpp::string_view(arg, index));
+    nan_mantissa = static_cast<StorageType>(nan_mantissa_result);
+  }
+
+  result = FPBits(result.build_quiet_nan(nan_mantissa));
+  return {T(result), 0, error};
+}
+
 } // namespace internal
 } // namespace LIBC_NAMESPACE
 

libc/src/math/CMakeLists.txt

@@ -179,6 +179,10 @@ add_math_entrypoint_object(modf)
 add_math_entrypoint_object(modff)
 add_math_entrypoint_object(modfl)
 
+add_math_entrypoint_object(nan)
+add_math_entrypoint_object(nanf)
+add_math_entrypoint_object(nanl)
+
 add_math_entrypoint_object(nearbyint)
 add_math_entrypoint_object(nearbyintf)
 add_math_entrypoint_object(nearbyintl)

libc/src/math/generic/CMakeLists.txt

@@ -1437,6 +1437,45 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  nan
+  SRCS
+    nan.cpp
+  HDRS
+    ../nan.h
+  DEPENDS
+    libc.src.__support.str_to_float
+    libc.src.errno.errno
+  COMPILE_OPTIONS
+    -O3
+)
+
+add_entrypoint_object(
+  nanf
+  SRCS
+    nanf.cpp
+  HDRS
+    ../nanf.h
+  DEPENDS
+    libc.src.__support.str_to_float
+    libc.src.errno.errno
+  COMPILE_OPTIONS
+    -O3
+)
+
+add_entrypoint_object(
+  nanl
+  SRCS
+    nanl.cpp
+  HDRS
+    ../nanl.h
+  DEPENDS
+    libc.src.__support.str_to_float
+    libc.src.errno.errno
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   nextafter
   SRCS

libc/src/math/generic/nan.cpp

@@ -0,0 +1,23 @@
+//===-- Implementation of nan function ------------------------------------===//
+//
+// 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/math/nan.h"
+#include "src/__support/common.h"
+#include "src/__support/str_to_float.h"
+#include "src/errno/libc_errno.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(double, nan, (const char *arg)) {
+  auto result = internal::strtonan<double>(arg);
+  if (result.has_error())
+    libc_errno = result.error;
+  return result.value;
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/math/generic/nanf.cpp

@@ -0,0 +1,23 @@
+//===-- Implementation of nanf function -----------------------------------===//
+//
+// 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/math/nanf.h"
+#include "src/__support/common.h"
+#include "src/__support/str_to_float.h"
+#include "src/errno/libc_errno.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(float, nanf, (const char *arg)) {
+  auto result = internal::strtonan<float>(arg);
+  if (result.has_error())
+    libc_errno = result.error;
+  return result.value;
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/math/generic/nanl.cpp

@@ -0,0 +1,23 @@
+//===-- Implementation of nanl function -----------------------------------===//
+//
+// 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/math/nanl.h"
+#include "src/__support/common.h"
+#include "src/__support/str_to_float.h"
+#include "src/errno/libc_errno.h"
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(long double, nanl, (const char *arg)) {
+  auto result = internal::strtonan<long double>(arg);
+  if (result.has_error())
+    libc_errno = result.error;
+  return result.value;
+}
+
+} // namespace LIBC_NAMESPACE

libc/src/math/nan.h

@@ -0,0 +1,18 @@
+//===-- Implementation header for nan ---------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_NAN_H
+#define LLVM_LIBC_SRC_MATH_NAN_H
+
+namespace LIBC_NAMESPACE {
+
+double nan(const char *arg);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_NAN_H

libc/src/math/nanf.h

@@ -0,0 +1,18 @@
+//===-- Implementation header for nanf --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_NANF_H
+#define LLVM_LIBC_SRC_MATH_NANF_H
+
+namespace LIBC_NAMESPACE {
+
+float nanf(const char *arg);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_NANF_H

libc/src/math/nanl.h

@@ -0,0 +1,18 @@
+//===-- Implementation header for nanl --------------------------*- C++ -*-===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_NANL_H
+#define LLVM_LIBC_SRC_MATH_NANL_H
+
+namespace LIBC_NAMESPACE {
+
+long double nanl(const char *arg);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_NANL_H

libc/test/src/math/smoke/CMakeLists.txt

@@ -1203,6 +1203,45 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  nanf_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    nanf_test.cpp
+  DEPENDS
+    libc.include.math
+    libc.include.signal
+    libc.src.math.nanf
+    libc.src.__support.FPUtil.fp_bits
+)
+
+add_fp_unittest(
+  nan_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    nan_test.cpp
+  DEPENDS
+    libc.include.math
+    libc.include.signal
+    libc.src.math.nan
+    libc.src.__support.FPUtil.fp_bits
+)
+
+add_fp_unittest(
+  nanl_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    nanl_test.cpp
+  DEPENDS
+    libc.include.math
+    libc.include.signal
+    libc.src.math.nanl
+    libc.src.__support.FPUtil.fp_bits
+)
+
 # FIXME: These tests are currently spurious for NVPTX.
 if(NOT LIBC_GPU_TARGET_ARCHITECTURE_IS_NVPTX)
   add_fp_unittest(

libc/test/src/math/smoke/nan_test.cpp

@@ -0,0 +1,47 @@
+//===-- Unittests for nan -------------------------------------------------===//
+//
+// 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/FPUtil/FPBits.h"
+#include "src/math/nan.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include <signal.h>
+
+class LlvmLibcNanTest : public LIBC_NAMESPACE::testing::Test {
+public:
+  using StorageType = LIBC_NAMESPACE::fputil::FPBits<double>::StorageType;
+
+  void run_test(const char *input_str, StorageType bits) {
+    double result = LIBC_NAMESPACE::nan(input_str);
+    auto actual_fp = LIBC_NAMESPACE::fputil::FPBits<double>(result);
+    auto expected_fp = LIBC_NAMESPACE::fputil::FPBits<double>(bits);
+    EXPECT_EQ(actual_fp.bits, expected_fp.bits);
+  };
+};
+
+TEST_F(LlvmLibcNanTest, NCharSeq) {
+  run_test("", 0x7ff8000000000000);
+  run_test("1234", 0x7ff80000000004d2);
+  run_test("0x1234", 0x7ff8000000001234);
+  run_test("1a", 0x7ff8000000000000);
+  run_test("1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM_",
+           0x7ff8000000000000);
+  run_test("10000000000000000000000000000000000000000000000000",
+           0x7ff8000000000000);
+}
+
+TEST_F(LlvmLibcNanTest, RandomString) {
+  run_test(" 1234", 0x7ff8000000000000);
+  run_test("-1234", 0x7ff8000000000000);
+  run_test("asd&f", 0x7ff8000000000000);
+  run_test("123 ", 0x7ff8000000000000);
+}
+
+TEST_F(LlvmLibcNanTest, InvalidInput) {
+  EXPECT_DEATH([] { LIBC_NAMESPACE::nan(nullptr); }, WITH_SIGNAL(SIGSEGV));
+}

libc/test/src/math/smoke/nanf_test.cpp

@@ -0,0 +1,46 @@
+//===-- Unittests for nanf ------------------------------------------------===//
+//
+// 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/FPUtil/FPBits.h"
+#include "src/math/nanf.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include <signal.h>
+
+class LlvmLibcNanfTest : public LIBC_NAMESPACE::testing::Test {
+public:
+  using StorageType = LIBC_NAMESPACE::fputil::FPBits<float>::StorageType;
+
+  void run_test(const char *input_str, StorageType bits) {
+    float result = LIBC_NAMESPACE::nanf(input_str);
+    auto actual_fp = LIBC_NAMESPACE::fputil::FPBits<float>(result);
+    auto expected_fp = LIBC_NAMESPACE::fputil::FPBits<float>(bits);
+    EXPECT_EQ(actual_fp.bits, expected_fp.bits);
+  };
+};
+
+TEST_F(LlvmLibcNanfTest, NCharSeq) {
+  run_test("", 0x7fc00000);
+  run_test("1234", 0x7fc004d2);
+  run_test("0x1234", 0x7fc01234);
+  run_test("1a", 0x7fc00000);
+  run_test("1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM_",
+           0x7fc00000);
+  run_test("10000000000000000000000000000000000000000000000000", 0x7fc00000);
+}
+
+TEST_F(LlvmLibcNanfTest, RandomString) {
+  run_test(" 1234", 0x7fc00000);
+  run_test("-1234", 0x7fc00000);
+  run_test("asd&f", 0x7fc00000);
+  run_test("123 ", 0x7fc00000);
+}
+
+TEST_F(LlvmLibcNanfTest, InvalidInput) {
+  EXPECT_DEATH([] { LIBC_NAMESPACE::nanf(nullptr); }, WITH_SIGNAL(SIGSEGV));
+}

libc/test/src/math/smoke/nanl_test.cpp

@@ -0,0 +1,72 @@
+//===-- Unittests for nanl ------------------------------------------------===//
+//
+// 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/FPUtil/FPBits.h"
+#include "src/math/nanl.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include <signal.h>
+
+#if defined(LIBC_LONG_DOUBLE_IS_FLOAT64)
+#define SELECT_LONG_DOUBLE(val, _, __) val
+#elif defined(LIBC_LONG_DOUBLE_IS_X86_FLOAT80)
+#define SELECT_LONG_DOUBLE(_, val, __) val
+#else
+#define SELECT_LONG_DOUBLE(_, __, val) val
+#endif
+
+class LlvmLibcNanlTest : public LIBC_NAMESPACE::testing::Test {
+public:
+  using StorageType = LIBC_NAMESPACE::fputil::FPBits<long double>::StorageType;
+
+  void run_test(const char *input_str, StorageType bits) {
+    long double result = LIBC_NAMESPACE::nanl(input_str);
+    auto actual_fp = LIBC_NAMESPACE::fputil::FPBits<long double>(result);
+    auto expected_fp = LIBC_NAMESPACE::fputil::FPBits<long double>(bits);
+    EXPECT_EQ(actual_fp.bits, expected_fp.bits);
+  };
+};
+
+TEST_F(LlvmLibcNanlTest, NCharSeq) {
+  run_test("",
+           SELECT_LONG_DOUBLE(0x7ff8000000000000, (UInt128(0x7fffc00000) << 40),
+                              (UInt128(0x7fff800000000000) << 64)));
+  run_test("1234", SELECT_LONG_DOUBLE(
+                       0x7ff80000000004d2,
+                       (UInt128(0x7fffc00000) << 40) + UInt128(0x4d2),
+                       (UInt128(0x7fff800000000000) << 64) + UInt128(0x4d2)));
+  run_test("0x1234",
+           SELECT_LONG_DOUBLE(0x7ff8000000001234,
+                              (UInt128(0x7fffc00000) << 40) + UInt128(0x1234),
+                              (UInt128(0x7fff800000000000) << 64) +
+                                  UInt128(0x1234)));
+  run_test("1a",
+           SELECT_LONG_DOUBLE(0x7ff8000000000000, (UInt128(0x7fffc00000) << 40),
+                              (UInt128(0x7fff800000000000) << 64)));
+  run_test("1234567890qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM_",
+           SELECT_LONG_DOUBLE(0x7ff8000000000000, (UInt128(0x7fffc00000) << 40),
+                              (UInt128(0x7fff800000000000) << 64)));
+  run_test("10000000000000000000000000000000000000000000000000",
+           SELECT_LONG_DOUBLE(0x7ff8000000000000, (UInt128(0x7fffc00000) << 40),
+                              (UInt128(0x7fff800000000000) << 64)));
+}
+
+TEST_F(LlvmLibcNanlTest, RandomString) {
+  StorageType expected =
+      SELECT_LONG_DOUBLE(0x7ff8000000000000, (UInt128(0x7fffc00000) << 40),
+                         (UInt128(0x7fff800000000000) << 64));
+
+  run_test(" 1234", expected);
+  run_test("-1234", expected);
+  run_test("asd&f", expected);
+  run_test("123 ", expected);
+}
+
+TEST_F(LlvmLibcNanlTest, InvalidInput) {
+  EXPECT_DEATH([] { LIBC_NAMESPACE::nanl(nullptr); }, WITH_SIGNAL(SIGSEGV));
+}

utils/bazel/llvm-project-overlay/libc/BUILD.bazel

@@ -1874,6 +1874,12 @@ libc_math_function(name = "llroundf")
 
 libc_math_function(name = "llroundl")
 
+libc_math_function(name = "nan")
+
+libc_math_function(name = "nanf")
+
+libc_math_function(name = "nanl")
+
 libc_math_function(name = "nearbyint")
 
 libc_math_function(name = "nearbyintf")