A set of bytes to search for, any number of them. Make it once with make_byte_set.
Fields
- low: [2] u8x16
- per low nibble: the buckets holding a byte with that low nibble
- high: [2] u8x16
- per high nibble: its bucket bit
- wide: bool
- the bytes have more than 8 high nibbles, so both table pairs are used
- single: s16
- the set's only byte, or -1: then a plain compare finds it
- bits: [32] u8
- membership, one bit per byte