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Re: Even faster Unicode character counting

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From:
karl williamson
Date:
December 30, 2008 16:56
Subject:
Re: Even faster Unicode character counting
Message ID:
495AC336.3070607@khwilliamson.com
David Nicol wrote:
> On Tue, Dec 30, 2008 at 12:39 PM, David Nicol <davidnicol@gmail.com> wrote:
>> Here's an ifdeffed version that attempts to use vectorization to skip
>> runs of invariants quickly while still using the information from the
>> start bytes to skip ahead, for the EBCDIC channel.  And I corrected
>> the off-by-one in the comment.  This compiles, but I have neither
>> tested nor benchmarked.
> 
> open note to self:
> Sent a patch without even testing?  What kind of idiot are you trying
> to pass yourself off as, anyway?
> I tested your patch and discovered that you had an off-by-one -- your
> initializing count to -1 was based on a misunderstanding of how the
> function is used!
> end open note to self
> 
> But there's a thing I don't quite get -- the UTFSKIP lookup table
> assigns a length of 13 to a 0xFF start byte.  Could someone explain
> how that works?  The tests pertaining to length now work, but tests
> presumably based on the functionality involved in this 13-long thing
> are now failing, as that uses a different mechanism than counting
> continuation bytes can handle.
> 
> 
0xff is an illegal start byte.  Here's some info:
http://en.wikipedia.org/wiki/UTF-8

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