How to find offsets in Unicode Text fast

Niggemann, Bernd Bernd.Niggemann at uni-wh.de
Sat Nov 10 15:12:52 EST 2018


I figured that the slowdown was due to UTF8, for each char it has to test if it is a compounded character. So I just tried with utf16 figuring, that now it just compares at the byte-level.

As it turned out it was indeed faster.

Now I don't understand unicode but as I understand for some languages/signs/characters you need UTF32 to display them correctly. I may be wrong on that. But if it is true then the overhead to use UTF32 in textEncoding only adds a small amount to processing time.

The nice thing is that UTF16 and UTF32 textencoding also support caseSensitivity.  ByteOffset() for UTF16 is probably always case-sensitive, but only saves a small amount of processing time.

Also, LC apparently has to turn ASCII into UTF8 as soon as there is one non-ASCII character in the source text. In my naive understanding LC could internally switch to UTF16/32 for offset() as soon as it realizes that UTF8 is in the source. Would make obsolete this workaround.


This is just how I "think" it works, the explanation may be all wrong.

Kind regards

Bernd

Am 10.11.2018 um 20:30 schrieb Geoff Canyon <gcanyon at gmail.com<mailto:gcanyon at gmail.com>>:

This is faster -- under some circumstances, much faster! Any idea why textEncoding suddenly fixes everything?

On Sat, Nov 10, 2018 at 5:13 AM Niggemann, Bernd via use-livecode <use-livecode at lists.runrev.com<mailto:use-livecode at lists.runrev.com>> wrote:
This is a little late but there was a discussion about the slowness of simple offset() when dealing with text that contains Unicode characters.

Geoff Canyon and Brian Milby found a faster solution by setting the itemDelimiter to the search string.
They even provided a way to find the position of substrings in the search string which the offset() command does by design.

Here I propose a variant of the offset() form that uses UTF16 to search, easily adaptable to UTF32 if necessary.

To test (as in Brian's testStack) add a unicode character to the text to be searched e.g. at the end. Just any non-ASCII character to see the speed penalty of simple offset(). I used ð (Icelandic d) or use any chinese character.


Kind regards
Bernd

-------------------------------------------
function allOffsets pDelim, pString, pCaseSensitive
   local tNewPos, tPos, tResult

   put textEncode(pDelim,"UTF16") into pDelim
   put textEncode(pString,"UTF16") into pString

   set the caseSensitive to pCaseSensitive is true
   put 0 into tPos
   repeat forever
      put offset(pDelim, pString, tPos) into tNewPos
      if tNewPos = 0 then exit repeat
      add tNewPos to tPos
      put tPos div 2 + tPos mod 2,"" after tResult
   end repeat
   if tResult is empty then return 0
   else return char 1 to -2 of tResult
end allOffsets
-----------------------------------------
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