julia> using Random, BenchmarkTools
   julia> function isvowel(c)
            idx = (c | 0x20) - Int('a')
            return (0x00104111 & (1 << idx)) != 0
         end

   julia> hasvowel(str) = any(c -> isvowel(Int(c)), str)

   julia> @btime hasvowel(s) setup=(s=randstring("bcdfghjklmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ0123456789", 10))
   15.739 ns (0 allocations: 0 bytes)
   false

str|0x32 if you want case-insensitive.

This works because the lowest five bits, more specifically bits two to five, of the vowels are distinct.

The lut is zeroed except for the indices corresponding to the vowels, which contain it self: lut[vowel&31]=vowel or lut[(vowel&31)>>1]=vowel

- Setting bit 5 high forces lowercase for the input letter

- masking with `& 31` gives an index from 0-25 for the input letter

Then you can the `bt` instruction (in x86_64) to bit-test against the set of bits for a,e,i,o,u (after lowercasing) and return whether it matches, in a single instruction.

It came up with this, which I thought was pretty nice: https://godbolt.org/z/KjMdz99be

I'm sure there's other cool ways to test multiple vowels at once using AVX2 or AVX-512, I didn't really get that far. I just thought the bit-test trick was pretty sweet.

Chat transcript is here (it failed pretty spectacularly the first couple times, tripping over AT&T syntax and getting an off-by-one error, but still pretty good) https://chatgpt.com/share/684c8b39-a9c4-8012-8bb6-74e1f8b6d0...

You can do extremely trivial binary checks on ASCII, UTF-8 (and most? other) encoding schemes. All vowels including W and Y contain a 1 in the lowest bit. Then by comparing bits 1-4, you can do a trivial case-insensitive comparison. You detect case by checking bit 5. 0 is upper, 1 is lower.