How to find offsets in Unicode Text fast

Geoff Canyon gcanyon at gmail.com
Sat Nov 10 18:00:32 EST 2018


Unfortunately, I just discovered that your solution doesn't produce correct
results. If I get the offsets of "aaaaaaaaaa" in
"↘𠜎aa↘𠜎aaaaaaaaaaaaa↘𠜎aaaa",

My code (and Brian Milby's) will return: 7,8,9,10

Your code will return: 9,10,11,12

As I understand it, textEncode transforms unicode text into binary data,
which has the effect of speeding things up because LC is no longer dealing
with variable-byte-length characters, just the underlying (fixed-length)
binary data that makes them up. Hence the above discrepancy. At least I
think so. Maybe there's a way to fix it?

gc

On Sat, Nov 10, 2018 at 12:12 PM Niggemann, Bernd <Bernd.Niggemann at uni-wh.de>
wrote:

> 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>:
>
> 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> 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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>
>



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