[libc-commits] [libc] [libcxx] [libcxx][libc] Hand in Hand PoC with from_chars (PR #91651)
Michael Jones via libc-commits
libc-commits at lists.llvm.org
Thu May 9 13:33:04 PDT 2024
https://github.com/michaelrj-google created https://github.com/llvm/llvm-project/pull/91651
**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.
>From f8e8b05a48ac0df8695034153a35d9284ac6184b 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] [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 fd7eb125e007b..a528cddf0cb53 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -249,6 +249,7 @@ 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 8b28d1b891895..15fc83b893056 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
@@ -197,7 +198,7 @@ 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
PRIVATE ${LIBCXX_LIBRARIES})
set_target_properties(cxx_shared
@@ -285,7 +286,7 @@ 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
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...>)
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