hash16

    fn hash16(seed: u64, input: anytype, noalias secret: *const [192]u8) u64 {
        @branchHint(.unlikely);
        std.debug.assert(input.len > 8 and input.len <= 16);

        const flip: [4]u64 = @bitCast(secret[24..56].*);
        const blk: [2]u64 = @bitCast([_][8]u8{
            input[0..8].*,
            input[input.len - 8 ..][0..8].*,
        });

        const lo = blk[0] ^ ((flip[0] ^ flip[1]) +% seed);
        const hi = blk[1] ^ ((flip[2] ^ flip[3]) -% seed);
        const combined = @as(u64, input.len) +% @byteSwap(lo) +% hi +% fold(lo, hi);
        return avalanche(.h3, combined);
    }