At the risk of engaging in premature optimization, I would be inclined to suggest tuning for the common case, i.e. 7-or 8-bit ASCII. Setting up a bitmap for that is obviously straightforward. In practical terms you probably have to go with the list-of-pairs approach for the rest of the character set, since Unicode code points extend up to 0x10FFFF and I doubt you want to maintain a (very sparse) 1.1-megabit bit map for each character class.

And yes, that's 0x10FFFF, not 0xFFFF. Unicode is not limited to representing 64K characters, and something like 74K code points have actually been defined at this point. Short-term you could probably get away with only worrying about the lower 64K code points (the "basic multilingual plane"), but it's not really a compliant Unicode implementation if you go that route.

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

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