Iterating over Strings containing Unicode characters?

alias simd_width_u8 = simdwidthof[DType.uint8]()

fn rune_count_in_string(s: String) -> Int:
    var p = s._as_ptr().bitcast[DType.uint8]()
    var string_byte_length = len(s)
    var result = 0

    @parameter
    fn count[simd_width: Int](offset: Int):
        result += (
            ((p.load[width=simd_width](offset) >> 6) != 0b10)
            .cast[DType.uint8]()
            .reduce_add()
            .to_int()
        )

    vectorize[count, simd_width_u8](string_byte_length)
    return result