For Unicode (and a 64K bitmap's insufficient, there's more than 64K characters at this point) you can use a two or three level tree and compress away entire unused branches. There's some discussion of this in the Unicode spec, which is available online from The Unicode Consortium

Or go dig up PCRE, or IBM's ICU library.

In reply to Re: How are regex character classes implemented? by Elian
in thread How are regex character classes implemented? by John M. Dlugosz

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