[libcxx-commits] [libcxx] [libc++] Refactor basic_filebuf::overflow() (PR #144793)
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Fri Jun 20 09:02:55 PDT 2025
https://github.com/ldionne updated https://github.com/llvm/llvm-project/pull/144793
>From 73a7634f261d63e018ae338f53d7a308c2bc7006 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Tue, 17 Jun 2025 12:23:18 -0400
Subject: [PATCH 1/2] [libc++] Refactor basic_filebuf::overflow()
Refactor the function to streamline the logic so it matches the specification
in [filebuf.virtuals] more closely. In particular, avoid modifying the put
area pointers when we loop around after a partial codecvt conversion.
Note that we're technically not up-to-spec in this implementation, since
the Standard says that we shouldn't try more than once after a partial
codecvt conversion. However, this refactoring attempts not to change any
functionality.
---
libcxx/include/fstream | 57 ++++++++++++++++++++++++++----------------
1 file changed, 36 insertions(+), 21 deletions(-)
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
index 00aa00ff7e9cd..f9cbac2ab0578 100644
--- a/libcxx/include/fstream
+++ b/libcxx/include/fstream
@@ -835,35 +835,50 @@ typename basic_filebuf<_CharT, _Traits>::int_type basic_filebuf<_CharT, _Traits>
}
if (this->pptr() != this->pbase()) {
if (__always_noconv_) {
- size_t __nmemb = static_cast<size_t>(this->pptr() - this->pbase());
- if (std::fwrite(this->pbase(), sizeof(char_type), __nmemb, __file_) != __nmemb)
+ size_t __n = static_cast<size_t>(this->pptr() - this->pbase());
+ if (std::fwrite(this->pbase(), sizeof(char_type), __n, __file_) != __n)
return traits_type::eof();
} else {
- char* __extbe = __extbuf_;
- codecvt_base::result __r;
+ if (!__cv_)
+ std::__throw_bad_cast();
+
+ // See [filebuf.virtuals]
+ char_type* __b = this->pbase();
+ char_type* __p = this->pptr();
+ const char_type* __end;
+ char* __extbuf_end = __extbuf_;
do {
- if (!__cv_)
- std::__throw_bad_cast();
-
- const char_type* __e;
- __r = __cv_->out(__st_, this->pbase(), this->pptr(), __e, __extbuf_, __extbuf_ + __ebs_, __extbe);
- if (__e == this->pbase())
+ codecvt_base::result __r = __cv_->out(__st_, __b, __p, __end, __extbuf_, __extbuf_ + __ebs_, __extbuf_end);
+ if (__end == __b)
return traits_type::eof();
+
+ // No conversion needed: output characters directly to the file, done.
if (__r == codecvt_base::noconv) {
- size_t __nmemb = static_cast<size_t>(this->pptr() - this->pbase());
- if (std::fwrite(this->pbase(), 1, __nmemb, __file_) != __nmemb)
+ size_t __n = static_cast<size_t>(__p - __b);
+ if (std::fwrite(__b, 1, __n, __file_) != __n)
return traits_type::eof();
- } else if (__r == codecvt_base::ok || __r == codecvt_base::partial) {
- size_t __nmemb = static_cast<size_t>(__extbe - __extbuf_);
- if (std::fwrite(__extbuf_, 1, __nmemb, __file_) != __nmemb)
+ break;
+
+ // Conversion successful: output the converted characters to the file, done.
+ } else if (__r == codecvt_base::ok) {
+ size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
+ return traits_type::eof();
+ break;
+
+ // Conversion partially successful: output converted characters to the file and repeat with the
+ // remaining characters.
+ } else if (__r == codecvt_base::partial) {
+ size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
return traits_type::eof();
- if (__r == codecvt_base::partial) {
- this->setp(const_cast<char_type*>(__e), this->pptr());
- this->__pbump(this->epptr() - this->pbase());
- }
- } else
+ __b = const_cast<char_type*>(__end);
+ continue;
+
+ } else {
return traits_type::eof();
- } while (__r == codecvt_base::partial);
+ }
+ } while (true);
}
this->setp(__pb_save, __epb_save);
}
>From 98f6169a69fe647baf2aea537932724271841c46 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Fri, 20 Jun 2025 12:01:05 -0400
Subject: [PATCH 2/2] Use early return
---
libcxx/include/fstream | 92 ++++++++++++++++++++++--------------------
1 file changed, 48 insertions(+), 44 deletions(-)
diff --git a/libcxx/include/fstream b/libcxx/include/fstream
index f9cbac2ab0578..c86f709bedb80 100644
--- a/libcxx/include/fstream
+++ b/libcxx/include/fstream
@@ -833,55 +833,59 @@ typename basic_filebuf<_CharT, _Traits>::int_type basic_filebuf<_CharT, _Traits>
*this->pptr() = traits_type::to_char_type(__c);
this->pbump(1);
}
- if (this->pptr() != this->pbase()) {
- if (__always_noconv_) {
- size_t __n = static_cast<size_t>(this->pptr() - this->pbase());
- if (std::fwrite(this->pbase(), sizeof(char_type), __n, __file_) != __n)
+
+ // There is nothing to write, early return
+ if (this->pptr() == this->pbase()) {
+ return traits_type::not_eof(__c);
+ }
+
+ if (__always_noconv_) {
+ size_t __n = static_cast<size_t>(this->pptr() - this->pbase());
+ if (std::fwrite(this->pbase(), sizeof(char_type), __n, __file_) != __n)
+ return traits_type::eof();
+ } else {
+ if (!__cv_)
+ std::__throw_bad_cast();
+
+ // See [filebuf.virtuals]
+ char_type* __b = this->pbase();
+ char_type* __p = this->pptr();
+ const char_type* __end;
+ char* __extbuf_end = __extbuf_;
+ do {
+ codecvt_base::result __r = __cv_->out(__st_, __b, __p, __end, __extbuf_, __extbuf_ + __ebs_, __extbuf_end);
+ if (__end == __b)
return traits_type::eof();
- } else {
- if (!__cv_)
- std::__throw_bad_cast();
-
- // See [filebuf.virtuals]
- char_type* __b = this->pbase();
- char_type* __p = this->pptr();
- const char_type* __end;
- char* __extbuf_end = __extbuf_;
- do {
- codecvt_base::result __r = __cv_->out(__st_, __b, __p, __end, __extbuf_, __extbuf_ + __ebs_, __extbuf_end);
- if (__end == __b)
+
+ // No conversion needed: output characters directly to the file, done.
+ if (__r == codecvt_base::noconv) {
+ size_t __n = static_cast<size_t>(__p - __b);
+ if (std::fwrite(__b, 1, __n, __file_) != __n)
return traits_type::eof();
+ break;
- // No conversion needed: output characters directly to the file, done.
- if (__r == codecvt_base::noconv) {
- size_t __n = static_cast<size_t>(__p - __b);
- if (std::fwrite(__b, 1, __n, __file_) != __n)
- return traits_type::eof();
- break;
-
- // Conversion successful: output the converted characters to the file, done.
- } else if (__r == codecvt_base::ok) {
- size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
- if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
- return traits_type::eof();
- break;
-
- // Conversion partially successful: output converted characters to the file and repeat with the
- // remaining characters.
- } else if (__r == codecvt_base::partial) {
- size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
- if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
- return traits_type::eof();
- __b = const_cast<char_type*>(__end);
- continue;
-
- } else {
+ // Conversion successful: output the converted characters to the file, done.
+ } else if (__r == codecvt_base::ok) {
+ size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
return traits_type::eof();
- }
- } while (true);
- }
- this->setp(__pb_save, __epb_save);
+ break;
+
+ // Conversion partially successful: output converted characters to the file and repeat with the
+ // remaining characters.
+ } else if (__r == codecvt_base::partial) {
+ size_t __n = static_cast<size_t>(__extbuf_end - __extbuf_);
+ if (std::fwrite(__extbuf_, 1, __n, __file_) != __n)
+ return traits_type::eof();
+ __b = const_cast<char_type*>(__end);
+ continue;
+
+ } else {
+ return traits_type::eof();
+ }
+ } while (true);
}
+ this->setp(__pb_save, __epb_save);
return traits_type::not_eof(__c);
}
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