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    <ul> <li>Use PChar incrementing for speed of processing</li> <li>If some tokens are not needed, only copy token data on demand</li> <li>Copy PChar to local variable when actually scanning through characters</li> <li>Keep source data in a single buffer unless you must handle line by line, and even then, consider handling line processing as a separate token in the lexer recognizer</li> <li>Consider processing a byte array buffer that has come straight from the file, if you definitely know the encoding; if using Delphi 2009, use PAnsiChar instead of PChar, unless of course you know the encoding is UTF16-LE.</li> <li>If you know that the only whitespace is going to be #32 (ASCII space), or a similarly limited set of characters, there may be some clever bit manipulation hacks that can let you process 4 bytes at a time using Integer scanning. I wouldn't expect big wins here though, and the code will be as clear as mud.</li> </ul> <p>Here's a sample lexer that should be pretty efficient, but it assumes that all source data is in a single string. Reworking it to handle buffers is moderately tricky due to very long tokens.</p> <pre><code>type TLexer = class private FData: string; FTokenStart: PChar; FCurrPos: PChar; function GetCurrentToken: string; public constructor Create(const AData: string); function GetNextToken: Boolean; property CurrentToken: string read GetCurrentToken; end; { TLexer } constructor TLexer.Create(const AData: string); begin FData := AData; FCurrPos := PChar(FData); end; function TLexer.GetCurrentToken: string; begin SetString(Result, FTokenStart, FCurrPos - FTokenStart); end; function TLexer.GetNextToken: Boolean; var cp: PChar; begin cp := FCurrPos; // copy to local to permit register allocation // skip whitespace; this test could be converted to an unsigned int // subtraction and compare for only a single branch while (cp^ &gt; #0) and (cp^ &lt;= #32) do Inc(cp); // using null terminater for end of file Result := cp^ &lt;&gt; #0; if Result then begin FTokenStart := cp; Inc(cp); while cp^ &gt; #32 do Inc(cp); end; FCurrPos := cp; end; </code></pre>
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