Re: XML Memory Requirements (was Re: Feeling good about SML)
David Brownell wrote: > Tim Bray wrote: > > > > The performance is good enough that in Lark, the limiting factor was > > my lousy input buffering, not the character class checking; and Lark > > was always in the top half of the performance table. -Tim > > I think that's pretty typical. I've profiled several parsers by now, > and character class checking hasn't been a major issue ... usually > one or two percentage points CPU time for testing whether a character > works in a name (first/rest) or not. > > The technique I used in Sun's parser may be good for many folk to steal. > It involves using the standard Character.getType() method (which has > access to lots of Unicode tables, and in recent JVMs uses native code > to quickly access them) and then filtering that output by the rules in > the XML spec. That is one way to do it. What I found worked optimally in my case is to pregenerate a bitmap of all legal name and name start characters, save it to a file, and load it when using the XML parser into a constant array of integers (integer arrays in Java are faster to access because comparisons don't require a cast after retrieval). It takes up a little bit of extra memory but I think it is well worth it. Other Java XML parsers I have seen use a similiar approach except that the store the character bitmap in the class file itself which has the unfortunate problem of bloating the size of your class file immensely, and slowing down startup time because the stupid way Java deals with constant arrays of primitive types in classes is that it generates instructions for initializing each section of the array to the desired value instead of just having a stream of bytes that are read into the array one by one. I opted to initialize the array of name and namestart characters from a file because the startup time for the class was considerable as you needed to loop 128,000 times and test each index against a isNameChar() function or a isNameStartChar() function or something like that. I could use this method for testing whitespace as well as well as other characters, but it hardly seemed worthwhile because all of the whitespace characters can be tested with a switch/case statement and testing for all of the other special characters do not occur enough in an XML document to mandate adding another 2048 integers into memory. Tyler xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To unsubscribe, mailto:majordomo@i... the following message; unsubscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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