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POEfficient algorithm for converting a character set into a nfa/dfa
 

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    <p>I'm currently working on a scanner generator. The generator already works fine. But when using character classes the algorithm gets very slow.</p> <p>The scanner generator produces a scanner for UTF8 encoded files. The full range of characters (0x000000 to 0x10ffff) should be supported.</p> <p>If I use large character sets, like the any operator '.' or the unicode property {L}, the nfa (and also the dfa) contains a lot of states ( > 10000 ). So the convertation for nfa to dfa and create the minimal dfa takes a long time (even if the output minimal dfa contains only a few states). </p> <p>Here's my current implementation of creating a character set part of the nfa.</p> <pre><code>void CreateNfaPart(int startStateIndex, int endStateIndex, Set&lt;int&gt; characters) { transitions[startStateIndex] = CreateEmptyTransitionsArray(); foreach (int character in characters) { // get the utf8 encoded bytes for the character byte[] encoded = EncodingHelper.EncodeCharacter(character); int tStartStateIndex = startStateIndex; for (int i = 0; i &lt; encoded.Length - 1; i++) { int tEndStateIndex = transitions[tStartStateIndex][encoded[i]]; if (tEndStateIndex == -1) { tEndStateIndex = CreateState(); transitions[tEndStateIndex] = CreateEmptyTransitionsArray(); } transitions[tStartStateIndex][encoded[i]] = tEndStateIndex; tStartStateIndex = tEndStateIndex; } transitions[tStartStateIndex][encoded[encoded.Length - 1]] = endStateIndex; } </code></pre> <p>Does anyone know how to implement the function much more efficiently to create only the necessary states?</p> <p>EDIT:</p> <p>To be more specific I need a function like:</p> <pre><code>List&lt;Set&lt;byte&gt;[]&gt; Convert(Set&lt;int&gt; characters) { ??????? } </code></pre> <p>A helper function to convert a character (int) to a UTF8 encoding byte[] is defined as:</p> <pre><code>byte[] EncodeCharacter(int character) { ... } </code></pre>
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    1. COYou are building a xFA for the _byte_ input? Wouldn't it be a lot easier (and more reliable) to operate on (Utf16) chars?
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    2. COI don't think so, the size of the lookup table(s) would increase when using 16bit characters. Also the typical input file would be bigger if using utf16 (in comparision with utf8).
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    3. COI'm sorry, I misunderstood! Accepting any encoding would be a nice option for future version. But to keep it simple, I think it's easier to implement only one encoding, and UTF-8 looks like the right joice for me.
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