[libc++] Lets to_chars use header implementation.

[Mordante]

Summary

This removes the duplicated code from the dylib. Instead the dylib will
call the new functions in the header. Since this code is unneeded it's
removed from the unstable ABI.

Depends on D125704

[ldionne]

libcxx/include/__config

119–120

libcxx/src/ryu/d2s.cpp

529 ↗

(On Diff #429992)

To consider: If this increases our diff with "upstream" Ryu, it might be better to either #define __DIGIT_TABLE __itoa::__digits_base_10, or static constexpr auto& __DIGIT_TABLE = __itoa::__digits_base_10;.

[Mordante]

libcxx/src/ryu/d2s.cpp

529 ↗

(On Diff #429992)

As mentioned in the live review, since the code is in the dylib we can use inline constexpr instead of static constexpr

[Mordante]

Rebased and addresses review comments.

libcxx/include/__config

 // about ABI compatibility.
 #  define _LIBCPP_ABI_NO_RANDOM_DEVICE_COMPATIBILITY_LAYOUT
 // Don't export the legacy __basic_string_common class and its methods from the built library.
 #  define _LIBCPP_ABI_DO_NOT_EXPORT_BASIC_STRING_COMMON
 // Don't export the legacy __vector_base_common class and its methods from the built library.
 #  define _LIBCPP_ABI_DO_NOT_EXPORT_VECTOR_BASE_COMMON
 // According to the Standard, `bitset::operator[] const` returns bool
 #  define _LIBCPP_ABI_BITSET_VECTOR_BOOL_CONST_SUBSCRIPT_RETURN_BOOL
+// Remove the base 10 implementation of std::to_chars from the dylib.
+// The implementation moved to the header, but we still export the symbols from
+// the dylib for backwards compatibility.
+#  define _LIBCPP_ABI_DO_NOT_EXPORT_TO_CHARS_BASE_10
 #elif _LIBCPP_ABI_VERSION == 1
 #  if !defined(_LIBCPP_OBJECT_FORMAT_COFF)
 // Enable compiling copies of now inline methods into the dylib to support
 // applications compiled against older libraries. This is unnecessary with
 // COFF dllexport semantics, since dllexport forces a non-inline definition
 // of inline functions to be emitted anyway. Our own non-inline copy would
 // conflict with the dllexport-emitted copy, so we disable it.
 #    define _LIBCPP_DEPRECATED_ABI_LEGACY_LIBRARY_DEFINITIONS_FOR_INLINE_FUNCTIONS

libcxx/src/charconv.cpp

 //===----------------------------------------------------------------------===//
 //
 // 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 <charconv>
 #include <string.h>
 
-#include "include/ryu/digit_table.h"
 #include "include/to_chars_floating_point.h"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-namespace __itoa
-{
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append1(char* buffer, T i) noexcept
-{
-    *buffer = '0' + static_cast<char>(i);
-    return buffer + 1;
-}
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append2(char* buffer, T i) noexcept
-{
-    memcpy(buffer, &__DIGIT_TABLE[(i)*2], 2);
-    return buffer + 2;
-}
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append3(char* buffer, T i) noexcept
-{
-    return append2(append1(buffer, (i) / 100), (i) % 100);
-}
+#ifndef _LIBCPP_ABI_DO_NOT_EXPORT_TO_CHARS_BASE_10
 
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append4(char* buffer, T i) noexcept
-{
-    return append2(append2(buffer, (i) / 100), (i) % 100);
-}
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append2_no_zeros(char* buffer, T v) noexcept
-{
-    if (v < 10)
-        return append1(buffer, v);
-    else
-        return append2(buffer, v);
-}
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append4_no_zeros(char* buffer, T v) noexcept
-{
-    if (v < 100)
-        return append2_no_zeros(buffer, v);
-    else if (v < 1000)
-        return append3(buffer, v);
-    else
-        return append4(buffer, v);
-}
-
-template <typename T>
-inline _LIBCPP_INLINE_VISIBILITY char*
-append8_no_zeros(char* buffer, T v) noexcept
-{
-    if (v < 10000)
-    {
-        buffer = append4_no_zeros(buffer, v);
-    }
-    else
-    {
-        buffer = append4_no_zeros(buffer, v / 10000);
-        buffer = append4(buffer, v % 10000);
-    }
-    return buffer;
-}
+namespace __itoa
 
 _LIBCPP_FUNC_VIS char*
 __u32toa(uint32_t value, char* buffer) noexcept
 {
-    if (value < 100000000)
-    {
-        buffer = append8_no_zeros(buffer, value);
-    }
-    else
-    {
-        // value = aabbbbcccc in decimal
-        const uint32_t a = value / 100000000;  // 1 to 42
-        value %= 100000000;
-
-        buffer = append2_no_zeros(buffer, a);
-        buffer = append4(buffer, value / 10000);
-        buffer = append4(buffer, value % 10000);
-    }
-
-    return buffer;
+  return __base_10_u32(value, buffer);
 }
 
 _LIBCPP_FUNC_VIS char*
 __u64toa(uint64_t value, char* buffer) noexcept
 {
-    if (value < 100000000)
-    {
-        uint32_t v = static_cast<uint32_t>(value);
-        buffer = append8_no_zeros(buffer, v);
-    }
-    else if (value < 10000000000000000)
-    {
-        const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
-        const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
-
-        buffer = append8_no_zeros(buffer, v0);
-        buffer = append4(buffer, v1 / 10000);
-        buffer = append4(buffer, v1 % 10000);
-    }
-    else
-    {
-        const uint32_t a =
-            static_cast<uint32_t>(value / 10000000000000000);  // 1 to 1844
-        value %= 10000000000000000;
-
-        buffer = append4_no_zeros(buffer, a);
-
-        const uint32_t v0 = static_cast<uint32_t>(value / 100000000);
-        const uint32_t v1 = static_cast<uint32_t>(value % 100000000);
-        buffer = append4(buffer, v0 / 10000);
-        buffer = append4(buffer, v0 % 10000);
-        buffer = append4(buffer, v1 / 10000);
-        buffer = append4(buffer, v1 % 10000);
-    }
-
-    return buffer;
+  return __base_10_u64(value, buffer);
 }
 
 }  // namespace __itoa
 
+#endif // _LIBCPP_ABI_DO_NOT_EXPORT_TO_CHARS_BASE_10
+
 // The original version of floating-point to_chars was written by Microsoft and
 // contributed with the following license.
 
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 // This implementation is dedicated to the memory of Mary and Thavatchai.
 

libcxx/src/include/ryu/digit_table.h

 // SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
 // FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
 // ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
 
 #ifndef _LIBCPP_SRC_INCLUDE_RYU_DIGIT_TABLE_H
 #define _LIBCPP_SRC_INCLUDE_RYU_DIGIT_TABLE_H
 
-// Avoid formatting to keep the changes with the original code minimal.
-// clang-format off
-
+#include <__charconv/tables.h>
 #include <__config>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 // A table of all two-digit numbers. This is used to speed up decimal digit
 // generation by copying pairs of digits into the final output.
-inline constexpr char __DIGIT_TABLE[200] = {
-  '0','0','0','1','0','2','0','3','0','4','0','5','0','6','0','7','0','8','0','9',
-  '1','0','1','1','1','2','1','3','1','4','1','5','1','6','1','7','1','8','1','9',
-  '2','0','2','1','2','2','2','3','2','4','2','5','2','6','2','7','2','8','2','9',
-  '3','0','3','1','3','2','3','3','3','4','3','5','3','6','3','7','3','8','3','9',
-  '4','0','4','1','4','2','4','3','4','4','4','5','4','6','4','7','4','8','4','9',
-  '5','0','5','1','5','2','5','3','5','4','5','5','5','6','5','7','5','8','5','9',
-  '6','0','6','1','6','2','6','3','6','4','6','5','6','6','6','7','6','8','6','9',
-  '7','0','7','1','7','2','7','3','7','4','7','5','7','6','7','7','7','8','7','9',
-  '8','0','8','1','8','2','8','3','8','4','8','5','8','6','8','7','8','8','8','9',
-  '9','0','9','1','9','2','9','3','9','4','9','5','9','6','9','7','9','8','9','9'
-};
+//
+// In order to minimize the diff in the Ryu code between MSVC STL and libc++
+// the code uses the name __DIGIT_TABLE. In order to avoid code duplication it
+// reuses the table already available in libc++.
+inline constexpr auto& __DIGIT_TABLE = __itoa::__digits_base_10<>::__value;
 
 _LIBCPP_END_NAMESPACE_STD
 
-// clang-format on
-
 #endif // _LIBCPP_SRC_INCLUDE_RYU_DIGIT_TABLE_H