digest

        fn digest(noalias self: *Accumulator, total_len: u64, noalias last_block: *const InputBlock) u64 {
            const secret_block = self.secret[192 - block_bytes - 7 ..][0..block_bytes];
            round(&self.state, last_block, @ptrCast(secret_block));

            const merge_block: Block = @bitCast(self.secret[11 .. 11 + block_bytes].*);
            self.state ^= merge_block;

            var result = XxHash64.prime_1 *% total_len;
            inline for (0..4) |i| {
                result +%= fold(self.state[i * 2], self.state[i * 2 + 1]);
            }
            return avalanche(.h3, result);
        }