From: Anlai Lu <[email protected]>
Add partial specialization of _Iter_sink for ostreambuf_iterator
that inherits _Streambuf_sink, replacing per-character sputc with
bulk sputn and zero-copy put-area writes.
All counting and truncation (_M_max) is handled in this
specialization so that _Streambuf_sink stays a pure I/O layer.
_M_overflow counts all characters and only writes up to the limit,
so format_to_n can compute the total output length. _M_discarding
returns false for the same reason. Stack writes go through
_M_out._M_put() which tracks failure on the iterator. sputn
exceptions are caught and the iterator is marked failed via
_M_set_failed().
The maximum count uses size_t with _S_no_limit sentinel, matching
the _Ptr_sink convention and avoiding signed comparisons.
libstdc++-v3/ChangeLog:
* include/bits/streambuf_iterator.h (__format::_Iter_sink)
[__glibcxx_format]: Declare with specialization for
ostreambuf_iterator.
(std::ostreambuf_iterator) [__glibcxx_format]: Befriend
__format::_Iter_sink for ostreambuf_iterator.
* include/std/format (_Iter_sink<_CharT, ostreambuf_iterator<...>>):
Define new partial specialization.
Co-authored-by: Tomasz Kamiński <[email protected]>
Signed-off-by: Anlai Lu <[email protected]>
Signed-off-by: Tomasz Kamiński <[email protected]>
---
Changes in v2:
- limit unused/reserved buffer to the remaining characters
in _M_overflow/_M_reserve and constructor. Mostly via
calling _M_trim_buf. Rewrote _M_overflow in process
- overloads constructor without limit to avoid above
- befriend _Iter_sink specialization with ostreambuf_iterator
- remove _M_out member and recosntructor iterator in _M_finish
Testing on powerprc64. Tested on x86_64, additionally tested
*format* and *print* in all standard modes, assertions and
debug. OK for trunk?
.../include/bits/streambuf_iterator.h | 12 +++
libstdc++-v3/include/std/format | 82 +++++++++++++++++++
2 files changed, 94 insertions(+)
diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h
b/libstdc++-v3/include/bits/streambuf_iterator.h
index 095928ca4d8..d715edc24ae 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -42,6 +42,14 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
+#ifdef __glibcxx_format // C++ >= 20 && HOSTED
+ namespace __format {
+ template<typename, typename> class _Iter_sink;
+ template<typename _CharT, typename _Traits>
+ class _Iter_sink<_CharT, ostreambuf_iterator<_CharT, _Traits>>;
+ }
+#endif
+
/**
* @addtogroup iterators
* @{
@@ -266,6 +274,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
copy(istreambuf_iterator<_CharT2>, istreambuf_iterator<_CharT2>,
ostreambuf_iterator<_CharT2>);
+#ifdef __glibcxx_format // C++ >= 20 && HOSTED
+ friend class __format::_Iter_sink<char_type, ostreambuf_iterator>;
+#endif
+
private:
streambuf_type* _M_sbuf;
bool _M_failed;
diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
index 9223cd2e78b..ad6a56ecc3a 100644
--- a/libstdc++-v3/include/std/format
+++ b/libstdc++-v3/include/std/format
@@ -3847,6 +3847,88 @@ namespace __format
}
};
+ // Specialization replacing per-character sputc with bulk sputn
+ // and zero-copy writes into the streambuf's put area.
+ template<typename _CharT, typename _Traits>
+ class _Iter_sink<_CharT, ostreambuf_iterator<_CharT, _Traits>>
+ : public _Streambuf_sink<_CharT, _Traits>
+ {
+ using _Base = _Streambuf_sink<_CharT, _Traits>;
+ using _OutIter = ostreambuf_iterator<_CharT, _Traits>;
+
+ static constexpr size_t _S_no_limit = size_t(-1);
+
+ void
+ _M_trim_buf()
+ {
+ const size_t __avail = _M_max - _M_count;
+ if (this->_M_unused().size() > __avail)
+ this->_M_reset(this->_M_unused().first(__avail));
+ }
+
+ protected:
+ size_t _M_max = _S_no_limit;
+ size_t _M_count = 0;
+
+ void
+ _M_overflow() override
+ {
+ const size_t __new = this->_M_used().size();
+ if (_M_count >= _M_max)
+ this->_M_reset(this->_M_buf);
+ else if (size_t __a = _M_max - _M_count; __a > __new)
+ {
+ _Base::_M_overflow();
+ _M_trim_buf();
+ }
+ else
+ {
+ this->_M_flush();
+ this->_M_reset(this->_M_buf);
+ }
+ _M_count += __new;
+ }
+
+ bool
+ _M_discarding() const override
+ { return false; }
+
+ public:
+ [[__gnu__::__always_inline__]]
+ explicit
+ _Iter_sink(_OutIter __out)
+ : _Base(__out._M_sbuf)
+ { }
+
+ [[__gnu__::__always_inline__]]
+ explicit
+ _Iter_sink(_OutIter __out, iter_difference_t<_OutIter> __max)
+ : _Base(__out._M_sbuf), _M_max(__max < 0 ? _S_no_limit : size_t(__max))
+ { _M_trim_buf(); }
+
+ typename _Sink<_CharT>::_Reservation
+ _M_reserve(size_t __n) override
+ {
+ if (_M_count < _M_max)
+ if (size_t __a = _M_max - _M_count; __a >= __n)
+ return _Base::_M_reserve(__n);
+ return { nullptr };
+ }
+
+ format_to_n_result<_OutIter>
+ _M_finish() &&
+ {
+ _M_count += this->_M_used().size();
+ if (_M_count < _M_max)
+ this->_M_flush();
+
+ _OutIter __out;
+ __out._M_sbuf = this->_M_sbuf;
+ __out._M_failed = this->_M_write_failed;
+ return { std::move(__out), ptrdiff_t(_M_count) };
+ }
+ };
+
// Used for contiguous iterators.
// No buffer is used, characters are written straight to the iterator.
// We do not know the size of the output range, so the span size just grows
--
2.55.0
