A while back, I made some XML-related Regular Expressions for testing to see if a string is a legal XML identifier.

Easy to do in Perl, once you list all the ranges. Let the regex engine do the rest.

But now I need to do that in C++. I've been thinking of different ways to do it, ballancing both high-speed and compact representation.

A 64K bitmap (8K bytes) would be a simple lookup, but rather large. A list of pairs would be compact but slower to search. I'm leaning toward a hiarachial table of bitmaps.

So... how does Perl5 do it? In the old days, a 256-bit bitmap was a great character class implementation. But with Unicode, things change. I wonder if anyone knows what ideas were bantered around and dismissed, and why the implementors like the way they settled on (if they do)? Will Perl6 do it the same way?

—John

In reply to How are regex character classes implemented? by John M. Dlugosz

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