* Re: [External] Re: [PATCH] libstdc++: Optimize 'to_string<int>' with numeric_limits instead of __to_chars_len
[not found] <CALf+iit=6Te5ib9KUStJCb+Bz+7AtrjQjO9v49e=jc1-_7CqrA@mail.gmail.com>
@ 2021-09-15 19:44 ` Jonathan Wakely
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From: Jonathan Wakely @ 2021-09-15 19:44 UTC (permalink / raw)
To: 刘可; +Cc: libstdc++, gcc Patches
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N.B. Please CC *both* the libstdc++ list and the gcc-patches list, as
per https://gcc.gnu.org/lists.html
On Wed, 15 Sept 2021 at 14:02, 刘可 wrote:
>
> Thank you for your review, and I apologize for my mistake. I have updated and tested it!
Hmm, it doesn't work though. How did you test it?
For to_string(int) the string will be padded with '-' characters, i.e.
std::to_string(1) returns "1---------" and to_string(-1) returns
"-1---------" and to_string(100) returns "1--------00" !
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diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index b61fe05efcf..e1fd42aea1a 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -3716,41 +3716,82 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
// DR 1261. Insufficent overloads for to_string / to_wstring
+ namespace __detail
+ {
+ template<typename _Tp>
+ inline unsigned
+ __to_string_len(_Tp __val) noexcept
+ {
+#if _GLIBCXX_USE_CXX11_ABI
+ // Any 32-bit integer value fits in the 15-byte SSO buffer,
+ // so don't bother counting how many chars are needed.
+ if _GLIBCXX17_CONSTEXPR (sizeof(_Tp) * __CHAR_BIT_ <= 32)
+ return 9; // std::numeric_limits<uint32_t>::digits10
+ else
+#endif
+ return __detail::__to_chars_len(__uval);
+ }
+
+ inline void
+ __to_string_trim(string& __s) noexcept
+ {
+#if _GLIBCXX_USE_CXX11_ABI
+ ???
+#endif
+ }
+ }
+
inline string
to_string(int __val)
+#if _GLIBCXX_USE_CXX11_ABI
+ noexcept
+#endif
{
const bool __neg = __val < 0;
const unsigned __uval = __neg ? (unsigned)~__val + 1u : __val;
- const auto __len = __detail::__to_chars_len(__uval);
+ const auto __len = __detail::__to_string_len(__uval);
string __str(__neg + __len, '-');
__detail::__to_chars_10_impl(&__str[__neg], __len, __uval);
+ __detail::__to_string_trim(__str);
return __str;
}
inline string
to_string(unsigned __val)
+#if _GLIBCXX_USE_CXX11_ABI
+ noexcept
+#endif
{
- string __str(__detail::__to_chars_len(__val), '\0');
+ string __str(__detail::__to_string_len(__val), '\0');
__detail::__to_chars_10_impl(&__str[0], __str.size(), __val);
+ __detail::__to_string_trim(__str);
return __str;
}
inline string
to_string(long __val)
+#if _GLIBCXX_USE_CXX11_ABI && __SIZEOF_LONG__ == __SIZEOF_INT__
+ noexcept
+#endif
{
const bool __neg = __val < 0;
const unsigned long __uval = __neg ? (unsigned long)~__val + 1ul : __val;
- const auto __len = __detail::__to_chars_len(__uval);
+ const auto __len = __detail::__to_string_len(__uval);
string __str(__neg + __len, '-');
__detail::__to_chars_10_impl(&__str[__neg], __len, __uval);
+ __detail::__to_string_trim(__str);
return __str;
}
inline string
to_string(unsigned long __val)
+#if _GLIBCXX_USE_CXX11_ABI && __SIZEOF_LONG__ == __SIZEOF_INT__
+ noexcept
+#endif
{
- string __str(__detail::__to_chars_len(__val), '\0');
+ string __str(__detail::__to_string_len(__val), '\0');
__detail::__to_chars_10_impl(&__str[0], __str.size(), __val);
+ __detail::__to_string_trim(__str);
return __str;
}
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2021-09-15 19:44 ` [External] Re: [PATCH] libstdc++: Optimize 'to_string<int>' with numeric_limits instead of __to_chars_len Jonathan Wakely
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