[libcxx-commits] [libc] [libcxx] [llvm] [libcxx][libc] Hand in Hand PoC with from_chars (PR #91651)

Michael Jones via libcxx-commits libcxx-commits at lists.llvm.org
Tue Jul 30 13:23:52 PDT 2024


https://github.com/michaelrj-google updated https://github.com/llvm/llvm-project/pull/91651

>From 08de46ef7ed4d47ce7af473b5ea554d109811a9d Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Tue, 7 May 2024 16:50:24 -0700
Subject: [PATCH 1/4] [libcxx][libc] Hand in Hand PoC with from_chars

DO NOT MERGE, PROOF OF CONCEPT ONLY.

This patch aims to demonstrate the utility of sharing code between libc
and libc++ by using the libc float conversion code in the libc++
function from_chars. This patch adds from_chars for float and double
(long double is possible but was causing errors so was skipped here), as
well as a test to demonstrate that it works.

This is very much just a proof of concept, not intended to be committed
as-is. The from_chars code written is copied from the libc parsing code
and is not functionally complete, nor does it follow the correct coding
style.
---
 libc/shared/str_to_float.h                    |  29 ++++
 libcxx/include/CMakeLists.txt                 |   1 +
 .../__charconv/from_chars_floating_point.h    |  68 +++++++++
 libcxx/include/charconv                       |   1 +
 libcxx/src/CMakeLists.txt                     |   5 +-
 libcxx/src/charconv.cpp                       |  17 +++
 .../src/include/from_chars_floating_point.h   | 135 ++++++++++++++++++
 .../charconv.from.chars/float.pass.cpp        |  70 +++++++++
 libcxx/test/support/charconv_test_helpers.h   |   2 +
 9 files changed, 326 insertions(+), 2 deletions(-)
 create mode 100644 libc/shared/str_to_float.h
 create mode 100644 libcxx/include/__charconv/from_chars_floating_point.h
 create mode 100644 libcxx/src/include/from_chars_floating_point.h
 create mode 100644 libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp

diff --git a/libc/shared/str_to_float.h b/libc/shared/str_to_float.h
new file mode 100644
index 0000000000000..da70db11f6b82
--- /dev/null
+++ b/libc/shared/str_to_float.h
@@ -0,0 +1,29 @@
+//===-- String to float conversion utils ------------------------*- 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_SHARED_STR_TO_FLOAT_H
+#define LLVM_LIBC_SHARED_STR_TO_FLOAT_H
+
+#include "src/__support/str_to_float.h"
+
+namespace LIBC_NAMESPACE::shared {
+
+// WARNING: This is a proof of concept. In future the interface point for libcxx
+// won't be using libc internal classes.
+
+template <class T>
+inline internal::FloatConvertReturn<T> decimal_exp_to_float(
+    internal::ExpandedFloat<T> init_num, bool truncated,
+    internal::RoundDirection round, const char *__restrict num_start,
+    const size_t num_len = cpp::numeric_limits<size_t>::max()) {
+  return internal::decimal_exp_to_float(init_num, truncated, round, num_start,
+                                        num_len);
+}
+} // namespace LIBC_NAMESPACE::shared
+
+#endif // LLVM_LIBC_SHARED_STR_TO_FLOAT_H
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index 32579272858a8..43f9e5071f3b0 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -235,6 +235,7 @@ set(files
   __bit/rotate.h
   __bit_reference
   __charconv/chars_format.h
+  __charconv/from_chars_floating_point.h
   __charconv/from_chars_integral.h
   __charconv/from_chars_result.h
   __charconv/tables.h
diff --git a/libcxx/include/__charconv/from_chars_floating_point.h b/libcxx/include/__charconv/from_chars_floating_point.h
new file mode 100644
index 0000000000000..dd305ca8ea1dc
--- /dev/null
+++ b/libcxx/include/__charconv/from_chars_floating_point.h
@@ -0,0 +1,68 @@
+// -*- 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 _LIBCPP___CHARCONV_FROM_CHARS_FLOATING_POINT_H
+#define _LIBCPP___CHARCONV_FROM_CHARS_FLOATING_POINT_H
+
+#include <__assert>
+#include <__charconv/chars_format.h>
+#include <__charconv/from_chars_result.h>
+#include <__charconv/traits.h>
+#include <__config>
+#include <__system_error/errc.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/is_floating_point.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 17
+
+from_chars_result from_chars_floating_point(
+    const char* __first, const char* __last, float& value, chars_format fmt = chars_format::general);
+
+from_chars_result from_chars_floating_point(
+    const char* __first, const char* __last, double& value, chars_format fmt = chars_format::general);
+
+// template <typename _Tp, __enable_if_t<is_floating_point<_Tp>::value, int> = 0>
+// inline from_chars_result
+// from_chars(const char* __first, const char* __last, _Tp& __value, chars_format fmt = chars_format::general) {
+//   return std::from_chars_floating_point(__first, __last, __value, fmt);
+// }
+
+// inline from_chars_result
+// from_chars(const char* __first, const char* __last, float& __value, chars_format fmt = chars_format::general) {
+//   return std::from_chars_floating_point(__first, __last, __value, fmt);
+// }
+
+// inline from_chars_result
+// from_chars(const char* __first, const char* __last, double& __value, chars_format fmt = chars_format::general) {
+//   return std::from_chars_floating_point(__first, __last, __value, fmt);
+// }
+
+from_chars_result
+from_chars(const char* __first, const char* __last, float& __value, chars_format fmt = chars_format::general);
+
+from_chars_result
+from_chars(const char* __first, const char* __last, double& __value, chars_format fmt = chars_format::general);
+
+#endif // _LIBCPP_STD_VER >= 17
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___CHARCONV_FROM_CHARS_FLOATING_POINT_H
diff --git a/libcxx/include/charconv b/libcxx/include/charconv
index a2e270e9316dc..a8d5a5802d890 100644
--- a/libcxx/include/charconv
+++ b/libcxx/include/charconv
@@ -73,6 +73,7 @@ namespace std {
 
 #if _LIBCPP_STD_VER >= 17
 #  include <__charconv/chars_format.h>
+#  include <__charconv/from_chars_floating_point.h>
 #  include <__charconv/from_chars_integral.h>
 #  include <__charconv/from_chars_result.h>
 #  include <__charconv/tables.h>
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index fe9d2666fa4ca..41be5dcb2cbc4 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -31,6 +31,7 @@ set(LIBCXX_SOURCES
   include/ryu/f2s.h
   include/ryu/ryu.h
   include/to_chars_floating_point.h
+  include/from_chars_floating_point.h
   legacy_pointer_safety.cpp
   memory.cpp
   memory_resource.cpp
@@ -179,7 +180,7 @@ split_list(LIBCXX_LINK_FLAGS)
 # Build the shared library.
 if (LIBCXX_ENABLE_SHARED)
   add_library(cxx_shared SHARED ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
-  target_include_directories(cxx_shared PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_include_directories(cxx_shared PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/../../libc) #TODO: Do this properly
   target_link_libraries(cxx_shared PUBLIC cxx-headers libcxx-libc-shared
                                    PRIVATE ${LIBCXX_LIBRARIES})
   set_target_properties(cxx_shared
@@ -272,7 +273,7 @@ set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
 # Build the static library.
 if (LIBCXX_ENABLE_STATIC)
   add_library(cxx_static STATIC ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
-  target_include_directories(cxx_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_include_directories(cxx_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/../../libc) #TODO: Do this properly
   target_link_libraries(cxx_static PUBLIC cxx-headers libcxx-libc-static
                                    PRIVATE ${LIBCXX_LIBRARIES}
                                    PRIVATE libcxx-abi-static)
diff --git a/libcxx/src/charconv.cpp b/libcxx/src/charconv.cpp
index 4fd7a2c2c0f03..7d04de2dc4b35 100644
--- a/libcxx/src/charconv.cpp
+++ b/libcxx/src/charconv.cpp
@@ -9,6 +9,7 @@
 #include <charconv>
 #include <string.h>
 
+#include "include/from_chars_floating_point.h"
 #include "include/to_chars_floating_point.h"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
@@ -74,4 +75,20 @@ to_chars_result to_chars(char* __first, char* __last, long double __value, chars
       __first, __last, static_cast<double>(__value), __fmt, __precision);
 }
 
+from_chars_result from_chars_floating_point(const char* __first, const char* __last, float& value, chars_format fmt) {
+  return from_chars_floating_point<float>(__first, __last, value, fmt);
+}
+
+from_chars_result from_chars_floating_point(const char* __first, const char* __last, double& value, chars_format fmt) {
+  return from_chars_floating_point<double>(__first, __last, value, fmt);
+}
+
+from_chars_result from_chars(const char* __first, const char* __last, float& __value, chars_format fmt) {
+  return std::from_chars_floating_point(__first, __last, __value, fmt);
+}
+
+from_chars_result from_chars(const char* __first, const char* __last, double& __value, chars_format fmt) {
+  return std::from_chars_floating_point(__first, __last, __value, fmt);
+}
+
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/src/include/from_chars_floating_point.h b/libcxx/src/include/from_chars_floating_point.h
new file mode 100644
index 0000000000000..2efb3bcb4d780
--- /dev/null
+++ b/libcxx/src/include/from_chars_floating_point.h
@@ -0,0 +1,135 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
+#define _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
+
+// NEVER DO THIS FOR REAL, this is just for demonstration purposes.
+#define LIBC_NAMESPACE libc_namespace_in_libcxx
+
+// This header is in the shared LLVM-libc header library.
+#include "shared/str_to_float.h"
+
+#include <__assert>
+#include <__config>
+#include <charconv>
+#include <limits>
+#include <type_traits>
+
+// Included for the _Floating_type_traits class
+#include "to_chars_floating_point.h"
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <typename _Tp, __enable_if_t<std::is_floating_point<_Tp>::value, int> = 0>
+from_chars_result from_chars_floating_point(const char* __first, const char* __last, _Tp& value, chars_format fmt) {
+  using _Traits    = _Floating_type_traits<_Tp>;
+  using _Uint_type = typename _Traits::_Uint_type;
+  ptrdiff_t length = __last - __first;
+  _LIBCPP_ASSERT_INTERNAL(length > 0, "");
+
+  // hacky parsing code as example. Not intended for actual use. I'm just going to handle the base 10
+  // chars_format::general case. Also, no sign, inf, or nan handling.
+  _LIBCPP_ASSERT_INTERNAL(fmt == std::chars_format::general, "");
+
+  const char* src = __first; // rename to match the libc code copied for this section.
+
+  _Uint_type mantissa            = 0;
+  int exponent                   = 0;
+  bool truncated                 = false;
+  bool seen_digit                = false;
+  bool after_decimal             = false;
+  size_t index                   = 0;
+  const size_t BASE              = 10;
+  constexpr char EXPONENT_MARKER = 'e';
+  constexpr char DECIMAL_POINT   = '.';
+
+  // The loop fills the mantissa with as many digits as it can hold
+  const _Uint_type bitstype_max_div_by_base = numeric_limits<_Uint_type>::max() / BASE;
+  while (index < length) {
+    if (LIBC_NAMESPACE::internal::isdigit(src[index])) {
+      uint32_t digit = src[index] - '0';
+      seen_digit     = true;
+
+      if (mantissa < bitstype_max_div_by_base) {
+        mantissa = (mantissa * BASE) + digit;
+        if (after_decimal) {
+          --exponent;
+        }
+      } else {
+        if (digit > 0)
+          truncated = true;
+        if (!after_decimal)
+          ++exponent;
+      }
+
+      ++index;
+      continue;
+    }
+    if (src[index] == DECIMAL_POINT) {
+      if (after_decimal) {
+        break; // this means that src[index] points to a second decimal point, ending the number.
+      }
+      after_decimal = true;
+      ++index;
+      continue;
+    }
+    // The character is neither a digit nor a decimal point.
+    break;
+  }
+
+  if (!seen_digit)
+    return {src + index, {}};
+
+  if (index < length && LIBC_NAMESPACE::internal::tolower(src[index]) == EXPONENT_MARKER) {
+    bool has_sign = false;
+    if (index + 1 < length && (src[index + 1] == '+' || src[index + 1] == '-')) {
+      has_sign = true;
+    }
+    if (index + 1 + static_cast<size_t>(has_sign) < length &&
+        LIBC_NAMESPACE::internal::isdigit(src[index + 1 + static_cast<size_t>(has_sign)])) {
+      ++index;
+      auto result = LIBC_NAMESPACE::internal::strtointeger<int32_t>(src + index, 10);
+      // if (result.has_error())
+      //   output.error = result.error;
+      int32_t add_to_exponent = result.value;
+      index += result.parsed_len;
+
+      // Here we do this operation as int64 to avoid overflow.
+      int64_t temp_exponent = static_cast<int64_t>(exponent) + static_cast<int64_t>(add_to_exponent);
+
+      // If the result is in the valid range, then we use it. The valid range is
+      // also within the int32 range, so this prevents overflow issues.
+      if (temp_exponent > LIBC_NAMESPACE::fputil::FPBits<_Tp>::MAX_BIASED_EXPONENT) {
+        exponent = LIBC_NAMESPACE::fputil::FPBits<_Tp>::MAX_BIASED_EXPONENT;
+      } else if (temp_exponent < -LIBC_NAMESPACE::fputil::FPBits<_Tp>::MAX_BIASED_EXPONENT) {
+        exponent = -LIBC_NAMESPACE::fputil::FPBits<_Tp>::MAX_BIASED_EXPONENT;
+      } else {
+        exponent = static_cast<int32_t>(temp_exponent);
+      }
+    }
+  }
+
+  LIBC_NAMESPACE::internal::ExpandedFloat<_Tp> expanded_float = {0, 0};
+  if (mantissa != 0) {
+    auto temp = LIBC_NAMESPACE::shared::decimal_exp_to_float<_Tp>(
+        {mantissa, exponent}, truncated, LIBC_NAMESPACE::internal::RoundDirection::Nearest, src, length);
+    expanded_float = temp.num;
+    // Note: there's also an error value in temp.error. I'm not doing that error handling right now though.
+  }
+
+  auto result = LIBC_NAMESPACE::fputil::FPBits<_Tp>();
+  result.set_mantissa(expanded_float.mantissa);
+  result.set_biased_exponent(expanded_float.exponent);
+  value = result.get_val();
+  return {src + index, {}};
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif //_LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
new file mode 100644
index 0000000000000..3419fc478fec2
--- /dev/null
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+
+// <charconv>
+
+// constexpr from_chars_result from_chars(const char* first, const char* last,
+//                                        Float& value, chars_format fmt = chars_format::general)
+
+#include <charconv>
+#include "test_macros.h"
+#include "charconv_test_helpers.h"
+
+template <typename T>
+struct test_basics {
+  TEST_CONSTEXPR_CXX23 void operator()() {
+    std::from_chars_result r;
+    T x;
+
+    {
+      char s[] = "001x";
+
+      // the expected form of the subject sequence is a nonempty sequence of
+      // decimal digits optionally containing a decimal-point character, then
+      // an optional exponent part as defined in 6.4.4.3, excluding any digit
+      // separators (6.4.4.2); (C23 7.24.1.5)
+      r = std::from_chars(s, s + sizeof(s), x);
+      assert(r.ec == std::errc{});
+      assert(r.ptr == s + 3);
+      assert(x == T(1.0));
+    }
+
+    {
+      char s[] = "1.5e10";
+
+      r = std::from_chars(s, s + sizeof(s), x);
+      assert(r.ec == std::errc{});
+      assert(r.ptr == s + 6);
+      assert(x == T(1.5e10));
+    }
+
+    {
+      char s[] = "20040229";
+
+      // This number is halfway between two float values.
+      r = std::from_chars(s, s + sizeof(s), x);
+      assert(r.ec == std::errc{});
+      assert(r.ptr == s + 8);
+      assert(x == T(20040229));
+    }
+  }
+};
+
+TEST_CONSTEXPR_CXX23 bool test() {
+  run<test_basics>(all_floats);
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+
+  return 0;
+}
diff --git a/libcxx/test/support/charconv_test_helpers.h b/libcxx/test/support/charconv_test_helpers.h
index f5fbedbeb0dcd..fcae09478457b 100644
--- a/libcxx/test/support/charconv_test_helpers.h
+++ b/libcxx/test/support/charconv_test_helpers.h
@@ -317,6 +317,8 @@ auto all_unsigned = type_list<
     >();
 auto integrals = concat(all_signed, all_unsigned);
 
+auto all_floats = type_list< float, double >(); //TODO: Add long double
+
 template <template <typename> class Fn, typename... Ts>
 TEST_CONSTEXPR_CXX23 void
 run(type_list<Ts...>)

>From b5f244027be4d7f19d26e3f6901ce30b79084310 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Thu, 9 May 2024 16:04:43 -0700
Subject: [PATCH 2/4] fix warnings and add to modulemap

---
 libcxx/include/module.modulemap               | 19 ++++++++++---------
 .../src/include/from_chars_floating_point.h   |  8 ++++----
 2 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index 13d0dce34d97e..6c0ee59e2cc12 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -1075,18 +1075,19 @@ module std_private_bit_invert_if      [system] { header "__bit/invert_if.h" }
 module std_private_bit_popcount       [system] { header "__bit/popcount.h" }
 module std_private_bit_rotate         [system] { header "__bit/rotate.h" }
 
-module std_private_charconv_chars_format            [system] { header "__charconv/chars_format.h" }
-module std_private_charconv_from_chars_integral     [system] { header "__charconv/from_chars_integral.h" }
-module std_private_charconv_from_chars_result       [system] { header "__charconv/from_chars_result.h" }
-module std_private_charconv_tables                  [system] { header "__charconv/tables.h" }
-module std_private_charconv_to_chars                [system] { header "__charconv/to_chars.h" }
-module std_private_charconv_to_chars_base_10        [system] { header "__charconv/to_chars_base_10.h" }
-module std_private_charconv_to_chars_floating_point [system] { header "__charconv/to_chars_floating_point.h" }
-module std_private_charconv_to_chars_integral       [system] {
+module std_private_charconv_chars_format              [system] { header "__charconv/chars_format.h" }
+module std_private_charconv_from_chars_integral       [system] { header "__charconv/from_chars_integral.h" }
+module std_private_charconv_from_chars_result         [system] { header "__charconv/from_chars_result.h" }
+module std_private_charconv_tables                    [system] { header "__charconv/tables.h" }
+module std_private_charconv_to_chars                  [system] { header "__charconv/to_chars.h" }
+module std_private_charconv_to_chars_base_10          [system] { header "__charconv/to_chars_base_10.h" }
+module std_private_charconv_to_chars_floating_point   [system] { header "__charconv/to_chars_floating_point.h" }
+module std_private_charconv_from_chars_floating_point [system] { header "__charconv/from_chars_floating_point.h" }
+module std_private_charconv_to_chars_integral         [system] {
   header "__charconv/to_chars_integral.h"
   export std_private_charconv_traits
 }
-module std_private_charconv_to_chars_result         [system] {
+module std_private_charconv_to_chars_result           [system] {
   header "__charconv/to_chars_result.h"
   export *
 }
diff --git a/libcxx/src/include/from_chars_floating_point.h b/libcxx/src/include/from_chars_floating_point.h
index 2efb3bcb4d780..2a9f4bc84eb8c 100644
--- a/libcxx/src/include/from_chars_floating_point.h
+++ b/libcxx/src/include/from_chars_floating_point.h
@@ -51,7 +51,7 @@ from_chars_result from_chars_floating_point(const char* __first, const char* __l
 
   // The loop fills the mantissa with as many digits as it can hold
   const _Uint_type bitstype_max_div_by_base = numeric_limits<_Uint_type>::max() / BASE;
-  while (index < length) {
+  while (index < static_cast<size_t>(length)) {
     if (LIBC_NAMESPACE::internal::isdigit(src[index])) {
       uint32_t digit = src[index] - '0';
       seen_digit     = true;
@@ -86,12 +86,12 @@ from_chars_result from_chars_floating_point(const char* __first, const char* __l
   if (!seen_digit)
     return {src + index, {}};
 
-  if (index < length && LIBC_NAMESPACE::internal::tolower(src[index]) == EXPONENT_MARKER) {
+  if (index < static_cast<size_t>(length) && LIBC_NAMESPACE::internal::tolower(src[index]) == EXPONENT_MARKER) {
     bool has_sign = false;
-    if (index + 1 < length && (src[index + 1] == '+' || src[index + 1] == '-')) {
+    if (index + 1 < static_cast<size_t>(length) && (src[index + 1] == '+' || src[index + 1] == '-')) {
       has_sign = true;
     }
-    if (index + 1 + static_cast<size_t>(has_sign) < length &&
+    if (index + 1 + static_cast<size_t>(has_sign) < static_cast<size_t>(length) &&
         LIBC_NAMESPACE::internal::isdigit(src[index + 1 + static_cast<size_t>(has_sign)])) {
       ++index;
       auto result = LIBC_NAMESPACE::internal::strtointeger<int32_t>(src + index, 10);

>From 97ca620fe80a1691f33bc22033a20505b13b5161 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Fri, 24 May 2024 15:28:04 -0700
Subject: [PATCH 3/4] fix lint warnings and linkage errors

---
 .../__charconv/from_chars_floating_point.h    |  4 ++--
 libcxx/src/charconv.cpp                       | 20 +++++++++++--------
 .../src/include/from_chars_floating_point.h   |  6 +++---
 .../charconv.from.chars/float.pass.cpp        |  4 ++--
 4 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/libcxx/include/__charconv/from_chars_floating_point.h b/libcxx/include/__charconv/from_chars_floating_point.h
index dd305ca8ea1dc..d575dbbf611fe 100644
--- a/libcxx/include/__charconv/from_chars_floating_point.h
+++ b/libcxx/include/__charconv/from_chars_floating_point.h
@@ -32,10 +32,10 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 #if _LIBCPP_STD_VER >= 17
 
 from_chars_result from_chars_floating_point(
-    const char* __first, const char* __last, float& value, chars_format fmt = chars_format::general);
+    const char* __first, const char* __last, float& __value, chars_format __fmt = chars_format::general);
 
 from_chars_result from_chars_floating_point(
-    const char* __first, const char* __last, double& value, chars_format fmt = chars_format::general);
+    const char* __first, const char* __last, double& __value, chars_format __fmt = chars_format::general);
 
 // template <typename _Tp, __enable_if_t<is_floating_point<_Tp>::value, int> = 0>
 // inline from_chars_result
diff --git a/libcxx/src/charconv.cpp b/libcxx/src/charconv.cpp
index 7d04de2dc4b35..978ca4cde8c80 100644
--- a/libcxx/src/charconv.cpp
+++ b/libcxx/src/charconv.cpp
@@ -75,20 +75,24 @@ to_chars_result to_chars(char* __first, char* __last, long double __value, chars
       __first, __last, static_cast<double>(__value), __fmt, __precision);
 }
 
-from_chars_result from_chars_floating_point(const char* __first, const char* __last, float& value, chars_format fmt) {
-  return from_chars_floating_point<float>(__first, __last, value, fmt);
+from_chars_result
+from_chars_floating_point(const char* __first, const char* __last, float& __value, chars_format __fmt) {
+  return from_chars_floating_point<float>(__first, __last, __value, __fmt);
 }
 
-from_chars_result from_chars_floating_point(const char* __first, const char* __last, double& value, chars_format fmt) {
-  return from_chars_floating_point<double>(__first, __last, value, fmt);
+from_chars_result
+from_chars_floating_point(const char* __first, const char* __last, double& __value, chars_format __fmt) {
+  return from_chars_floating_point<double>(__first, __last, __value, __fmt);
 }
 
-from_chars_result from_chars(const char* __first, const char* __last, float& __value, chars_format fmt) {
-  return std::from_chars_floating_point(__first, __last, __value, fmt);
+_LIBCPP_EXPORTED_FROM_ABI from_chars_result
+from_chars(const char* __first, const char* __last, float& __value, chars_format __fmt) {
+  return from_chars_floating_point(__first, __last, __value, __fmt);
 }
 
-from_chars_result from_chars(const char* __first, const char* __last, double& __value, chars_format fmt) {
-  return std::from_chars_floating_point(__first, __last, __value, fmt);
+_LIBCPP_EXPORTED_FROM_ABI from_chars_result
+from_chars(const char* __first, const char* __last, double& __value, chars_format __fmt) {
+  return from_chars_floating_point(__first, __last, __value, __fmt);
 }
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/src/include/from_chars_floating_point.h b/libcxx/src/include/from_chars_floating_point.h
index 2a9f4bc84eb8c..fa6a2b3c5e534 100644
--- a/libcxx/src/include/from_chars_floating_point.h
+++ b/libcxx/src/include/from_chars_floating_point.h
@@ -27,7 +27,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <typename _Tp, __enable_if_t<std::is_floating_point<_Tp>::value, int> = 0>
-from_chars_result from_chars_floating_point(const char* __first, const char* __last, _Tp& value, chars_format fmt) {
+from_chars_result from_chars_floating_point(const char* __first, const char* __last, _Tp& __value, chars_format __fmt) {
   using _Traits    = _Floating_type_traits<_Tp>;
   using _Uint_type = typename _Traits::_Uint_type;
   ptrdiff_t length = __last - __first;
@@ -35,7 +35,7 @@ from_chars_result from_chars_floating_point(const char* __first, const char* __l
 
   // hacky parsing code as example. Not intended for actual use. I'm just going to handle the base 10
   // chars_format::general case. Also, no sign, inf, or nan handling.
-  _LIBCPP_ASSERT_INTERNAL(fmt == std::chars_format::general, "");
+  _LIBCPP_ASSERT_INTERNAL(__fmt == std::chars_format::general, "");
 
   const char* src = __first; // rename to match the libc code copied for this section.
 
@@ -126,7 +126,7 @@ from_chars_result from_chars_floating_point(const char* __first, const char* __l
   auto result = LIBC_NAMESPACE::fputil::FPBits<_Tp>();
   result.set_mantissa(expanded_float.mantissa);
   result.set_biased_exponent(expanded_float.exponent);
-  value = result.get_val();
+  __value = result.get_val();
   return {src + index, {}};
 }
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
index 3419fc478fec2..bf39f649084b0 100644
--- a/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
@@ -19,7 +19,7 @@
 
 template <typename T>
 struct test_basics {
-  TEST_CONSTEXPR_CXX23 void operator()() {
+  void operator()() {
     std::from_chars_result r;
     T x;
 
@@ -57,7 +57,7 @@ struct test_basics {
   }
 };
 
-TEST_CONSTEXPR_CXX23 bool test() {
+bool test() {
   run<test_basics>(all_floats);
 
   return true;

>From ae9736e472d8ae0a01bc1177a3e8419fc5bdd561 Mon Sep 17 00:00:00 2001
From: Michael Jones <michaelrj at google.com>
Date: Tue, 30 Jul 2024 13:17:09 -0700
Subject: [PATCH 4/4] address comments and create runtimes target

---
 .../__charconv/from_chars_floating_point.h    | 36 +++++++------------
 libcxx/include/charconv                       |  6 ++++
 libcxx/src/CMakeLists.txt                     | 10 +++---
 libcxx/src/charconv.cpp                       | 14 ++------
 .../src/include/from_chars_floating_point.h   |  3 --
 .../charconv.from.chars/float.pass.cpp        | 12 ++-----
 runtimes/cmake/Modules/FindLibcUtils.cmake    |  8 +++++
 7 files changed, 37 insertions(+), 52 deletions(-)
 create mode 100644 runtimes/cmake/Modules/FindLibcUtils.cmake

diff --git a/libcxx/include/__charconv/from_chars_floating_point.h b/libcxx/include/__charconv/from_chars_floating_point.h
index d575dbbf611fe..15fe88e64f2b5 100644
--- a/libcxx/include/__charconv/from_chars_floating_point.h
+++ b/libcxx/include/__charconv/from_chars_floating_point.h
@@ -31,33 +31,21 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER >= 17
 
-from_chars_result from_chars_floating_point(
-    const char* __first, const char* __last, float& __value, chars_format __fmt = chars_format::general);
+_LIBCPP_EXPORTED_FROM_ABI from_chars_result
+__from_chars_floating_point(const char* __first, const char* __last, float& __value, chars_format __fmt);
 
-from_chars_result from_chars_floating_point(
-    const char* __first, const char* __last, double& __value, chars_format __fmt = chars_format::general);
+_LIBCPP_EXPORTED_FROM_ABI from_chars_result
+__from_chars_floating_point(const char* __first, const char* __last, double& __value, chars_format __fmt);
 
-// template <typename _Tp, __enable_if_t<is_floating_point<_Tp>::value, int> = 0>
-// inline from_chars_result
-// from_chars(const char* __first, const char* __last, _Tp& __value, chars_format fmt = chars_format::general) {
-//   return std::from_chars_floating_point(__first, __last, __value, fmt);
-// }
+_LIBCPP_HIDE_FROM_ABI inline from_chars_result
+from_chars(const char* __first, const char* __last, float& __value, chars_format __fmt = chars_format::general) {
+  return std::__from_chars_floating_point(__first, __last, __value, __fmt);
+}
 
-// inline from_chars_result
-// from_chars(const char* __first, const char* __last, float& __value, chars_format fmt = chars_format::general) {
-//   return std::from_chars_floating_point(__first, __last, __value, fmt);
-// }
-
-// inline from_chars_result
-// from_chars(const char* __first, const char* __last, double& __value, chars_format fmt = chars_format::general) {
-//   return std::from_chars_floating_point(__first, __last, __value, fmt);
-// }
-
-from_chars_result
-from_chars(const char* __first, const char* __last, float& __value, chars_format fmt = chars_format::general);
-
-from_chars_result
-from_chars(const char* __first, const char* __last, double& __value, chars_format fmt = chars_format::general);
+_LIBCPP_HIDE_FROM_ABI inline from_chars_result
+from_chars(const char* __first, const char* __last, double& __value, chars_format __fmt = chars_format::general) {
+  return std::__from_chars_floating_point(__first, __last, __value, __fmt);
+}
 
 #endif // _LIBCPP_STD_VER >= 17
 
diff --git a/libcxx/include/charconv b/libcxx/include/charconv
index a8d5a5802d890..dfef8194a2a67 100644
--- a/libcxx/include/charconv
+++ b/libcxx/include/charconv
@@ -65,6 +65,12 @@ namespace std {
   constexpr from_chars_result from_chars(const char* first, const char* last,
                                see below& value, int base = 10);                         // constexpr since C++23
 
+  constexpr from_chars_result from_chars(const char* first, const char* last,
+                               float& value, chars_format fmt);
+
+  constexpr from_chars_result from_chars(const char* first, const char* last,
+                               double& value, chars_format fmt);
+
 } // namespace std
 
 */
diff --git a/libcxx/src/CMakeLists.txt b/libcxx/src/CMakeLists.txt
index 41be5dcb2cbc4..6183f42252d82 100644
--- a/libcxx/src/CMakeLists.txt
+++ b/libcxx/src/CMakeLists.txt
@@ -177,11 +177,13 @@ endif()
 split_list(LIBCXX_COMPILE_FLAGS)
 split_list(LIBCXX_LINK_FLAGS)
 
+include(FindLibcUtils)
+
 # Build the shared library.
 if (LIBCXX_ENABLE_SHARED)
   add_library(cxx_shared SHARED ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
-  target_include_directories(cxx_shared PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/../../libc) #TODO: Do this properly
-  target_link_libraries(cxx_shared PUBLIC cxx-headers libcxx-libc-shared
+  target_include_directories(cxx_shared PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_link_libraries(cxx_shared PUBLIC cxx-headers libcxx-libc-shared llvm-libc-shared-utilities
                                    PRIVATE ${LIBCXX_LIBRARIES})
   set_target_properties(cxx_shared
     PROPERTIES
@@ -273,8 +275,8 @@ set(CMAKE_STATIC_LIBRARY_PREFIX "lib")
 # Build the static library.
 if (LIBCXX_ENABLE_STATIC)
   add_library(cxx_static STATIC ${exclude_from_all} ${LIBCXX_SOURCES} ${LIBCXX_HEADERS})
-  target_include_directories(cxx_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_CURRENT_SOURCE_DIR}/../../libc) #TODO: Do this properly
-  target_link_libraries(cxx_static PUBLIC cxx-headers libcxx-libc-static
+  target_include_directories(cxx_static PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+  target_link_libraries(cxx_static PUBLIC cxx-headers libcxx-libc-static llvm-libc-shared-utilities
                                    PRIVATE ${LIBCXX_LIBRARIES}
                                    PRIVATE libcxx-abi-static)
   set_target_properties(cxx_static
diff --git a/libcxx/src/charconv.cpp b/libcxx/src/charconv.cpp
index 978ca4cde8c80..767b6cc9f28dd 100644
--- a/libcxx/src/charconv.cpp
+++ b/libcxx/src/charconv.cpp
@@ -76,23 +76,13 @@ to_chars_result to_chars(char* __first, char* __last, long double __value, chars
 }
 
 from_chars_result
-from_chars_floating_point(const char* __first, const char* __last, float& __value, chars_format __fmt) {
+__from_chars_floating_point(const char* __first, const char* __last, float& __value, chars_format __fmt) {
   return from_chars_floating_point<float>(__first, __last, __value, __fmt);
 }
 
 from_chars_result
-from_chars_floating_point(const char* __first, const char* __last, double& __value, chars_format __fmt) {
+__from_chars_floating_point(const char* __first, const char* __last, double& __value, chars_format __fmt) {
   return from_chars_floating_point<double>(__first, __last, __value, __fmt);
 }
 
-_LIBCPP_EXPORTED_FROM_ABI from_chars_result
-from_chars(const char* __first, const char* __last, float& __value, chars_format __fmt) {
-  return from_chars_floating_point(__first, __last, __value, __fmt);
-}
-
-_LIBCPP_EXPORTED_FROM_ABI from_chars_result
-from_chars(const char* __first, const char* __last, double& __value, chars_format __fmt) {
-  return from_chars_floating_point(__first, __last, __value, __fmt);
-}
-
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/src/include/from_chars_floating_point.h b/libcxx/src/include/from_chars_floating_point.h
index fa6a2b3c5e534..74a45d8a6fb2e 100644
--- a/libcxx/src/include/from_chars_floating_point.h
+++ b/libcxx/src/include/from_chars_floating_point.h
@@ -9,9 +9,6 @@
 #ifndef _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
 #define _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
 
-// NEVER DO THIS FOR REAL, this is just for demonstration purposes.
-#define LIBC_NAMESPACE libc_namespace_in_libcxx
-
 // This header is in the shared LLVM-libc header library.
 #include "shared/str_to_float.h"
 
diff --git a/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
index bf39f649084b0..2f13210702bea 100644
--- a/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
+++ b/libcxx/test/std/utilities/charconv/charconv.from.chars/float.pass.cpp
@@ -10,8 +10,8 @@
 
 // <charconv>
 
-// constexpr from_chars_result from_chars(const char* first, const char* last,
-//                                        Float& value, chars_format fmt = chars_format::general)
+// from_chars_result from_chars(const char* first, const char* last,
+//                              Float& value, chars_format fmt = chars_format::general)
 
 #include <charconv>
 #include "test_macros.h"
@@ -57,14 +57,8 @@ struct test_basics {
   }
 };
 
-bool test() {
-  run<test_basics>(all_floats);
-
-  return true;
-}
-
 int main(int, char**) {
-  test();
+  run<test_basics>(all_floats);
 
   return 0;
 }
diff --git a/runtimes/cmake/Modules/FindLibcUtils.cmake b/runtimes/cmake/Modules/FindLibcUtils.cmake
new file mode 100644
index 0000000000000..a1378401629fa
--- /dev/null
+++ b/runtimes/cmake/Modules/FindLibcUtils.cmake
@@ -0,0 +1,8 @@
+add_library(llvm-libc-shared-utilities INTERFACE)
+# TODO: Reorganize the libc shared section so that it can be included without
+# adding the root "libc" directory to the include path.
+# TODO: Find a better way to solve the problem that ${CMAKE_SOURCE_DIR} is
+# rooted in the runtimes directory, which is why we need the ".."
+target_include_directories(llvm-libc-shared-utilities INTERFACE ${CMAKE_SOURCE_DIR}/../libc) 
+target_compile_definitions(llvm-libc-shared-utilities INTERFACE LIBC_NAMESPACE=__llvm_libc_shared_utils)
+target_compile_features(llvm-libc-shared-utilities INTERFACE cxx_std_17)



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