[Webkit-unassigned] [Bug 84939] Optimize ASCII to UTF16 conversion using SSE2.

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=84939





--- Comment #20 from Huang Dongsung <luxtella at company100.net>  2012-04-27 05:03:21 PST ---
I will report some test results.

Although I said loading time of html5 spec page is 24s, when I downloaded html5 spec page and tested, loading time is 10s.
ASCII to UTF16 Decoding time is about 4ms, so "ASCII to UTF16 Decoding portion of loading time" is about 0.04%.
It is because ASCII to UTF16 Decoding is very cheap, that converts just 'xxyyzz' to '00xx00yy00zz'.

SSE2 increased about 20% performance, because SSE2 has some instructions for interleaving.

But when I implemented it using NEON, loading speed decreased from 25.7ms to  44.5ms in an android device. Whole loading time is about 44s.
NEON does not have proper interleaving instruction, so I had to copy a register to a register redundantly.

I think it was mistake to try to improve ASCII to UTF16 Decoding because it is cheap.


In addition, I tested a Korean site for checking real UTF8 to UTF16 decoding time.
http://navercast.naver.com/contents.nhn?contents_id=7865
Loading time is about 240ms, and decoding time is 0.42ms. The ratio is 0.175%.

The result is that webkit-builtin-text-decoding is too fast to optimize.

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