Tencent / rapidjson / 2080

100%

master: 100%

Pull #1424

travis-ci

Optimize FileReadStream and BasicIStreamWrapper.

On (my) linux, perftest reports:
- ~40% gain for FileReadStream (Take() loop),
- ~10% gain for ReaderParse_DummyHandler_FileReadStream.

With the same logic applied to BasicIStreamWrapper, which thus can now
also be created with a user buffer, performances align with those of
FileReadStream (same buffer size).

The "unbuffered" versions (added for FileReadStream) work solely with
the internal peekBuffer (Ch[4]) and are measured in perftest.  When
performances don't matter much, they can avoid the use of large
stack/heap buffers.

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4952 of 4967 relevant lines covered (99.7%)

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