void do_nothing(void) {Serial.println("nada");}

void (*interrupt_service_routines[])(void) = {
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing,
  do_nothing
};

volatile uint8_t inputs[3];

void register_ISR(uint32_t interrupt_mask, void (*isr)(void)) {
  PCICR = 0x0;    // disable pin change interrupts while we're making changes
  int8_t i = 0;
  do {
    if (interrupt_mask & (1L << i)) {
      interrupt_service_routines[i] = isr;
      if (i < 8) {            // D0 -- D7,   PCINT2
        PCMSK2 |= (1 << (i - 0));
        inputs[2] = PIND & PCMSK2;
        PCIFR = 0x4;  // write a 1 to *only* the relevant PCIFR bit
      } else if (i < 14) {    // D8 -- D13,  PCINT0
        PCMSK0 |= (1 << (i - 8));
        inputs[0] = PINB & PCMSK0;
        PCIFR = 0x2;
      } else {                // D14 -- D19, PCINT1
        PCMSK1 |= (1 << (i - 14));
        PCIFR = 0x1;
      }
    }
  } while (++i < 32);
  PCICR = 0x7;    // re-enable pin change interrupts
}

void deregister_ISR(uint32_t interrupt_mask) {
  PCICR = 0x0;    // disable pin change interrupts while we're making changes
  int8_t i = 0;
  do {
    if (interrupt_mask & (1 << i)) {
      interrupt_service_routines[i] = do_nothing;
      if (i < 8) {            // D0 -- D7,   PCINT2
        PCMSK2 &= ~(1 << (i - 0));
      } else if (i < 14) {    // D8 -- D13,  PCINT0
        PCMSK0 &= ~(1 << (i - 8));
      } else {                // D14 -- D19, PCINT1
        PCMSK1 &= ~(1 << (i - 14));
      }
    }
  } while (++i < 32);
  PCICR = 0x7;    // re-enable pin change interrupts
}

#define RUN_ISR(first_pin, last_pin, io_bank, new_inputs) do {  \
  uint8_t change = (new_inputs) ^ inputs[(io_bank)];            \
  switch (change) {                                             \
    case 0x01:                                                  \
      interrupt_service_routines[(first_pin) + 0]();            \
      break;                                                    \
    case 0x02:                                                  \
      interrupt_service_routines[(first_pin) + 1]();            \
      break;                                                    \
    case 0x04:                                                  \
      interrupt_service_routines[(first_pin) + 2]();            \
      break;                                                    \
    case 0x08:                                                  \
      interrupt_service_routines[(first_pin) + 3]();            \
      break;                                                    \
    case 0x10:                                                  \
      interrupt_service_routines[(first_pin) + 4]();            \
      break;                                                    \
    case 0x20:                                                  \
      interrupt_service_routines[(first_pin) + 5]();            \
      break;                                                    \
    case 0x40:                                                  \
      interrupt_service_routines[(first_pin) + 6]();            \
      break;                                                    \
    case 0x80:                                                  \
      interrupt_service_routines[(first_pin) + 7]();            \
      break;                                                    \
    default:                                                    \
      int8_t i = (first_pin);                                   \
      do {                                                      \
        if (change & 0x1) {                                     \
          interrupt_service_routines[i]();                      \
        }                                                       \
        change >>= 1;                                           \
        i++;                                                    \
      } while (i <= (last_pin));                                \
  }                                                             \
  inputs[(io_bank)] = (new_inputs);                             \
} while (0)

ISR(PCINT0_vect) {
  RUN_ISR(8, 13, 0, PINB & PCMSK0);
}
 
ISR(PCINT1_vect) {  // handle pin change interrupt for D14 to D19 here
  RUN_ISR(14, 19, 1, PINC & PCMSK1);
}  
 
ISR(PCINT2_vect) {  // handle pin change interrupt for D0 to D7 here
  RUN_ISR(0, 7, 2, PIND & PCMSK2);
}  

#define COWPI_PB  0                 //!< Index for arrays to access PINB/DDRB/PORTB and PCMSK0
#define D8_D13    0                 //!< Alias of COWPI_PB corresponding to pins D8-D13 on the Arduino Uno & Arduino Nano
#define COWPI_PC  1                 //!< Index for arrays to access PINC/DDRC/PORTC / PCMSK1
#define A0_A5     1                 //!< Alias of COWPI_PC for corresponding to pins D14-D19 (A0-A5) on the Arduino Uno & Arduino Nano
#define D14_D19   1                 //!< Alias of COWPI_PC for corresponding to pins D14-D19 (A0-A5) on the Arduino Uno & Arduino Nano
#define A0_A7     1                 //!< Alias of COWPI_PC for corresponding to pins D14-D19 (A0-A5) on the Arduino Uno & Arduino Nano
#define D14_D21   1                 //!< Alias of COWPI_PC for corresponding to pins D14-D19 (A0-A5) on the Arduino Uno & Arduino Nano
#define COWPI_PD  2                 //!< Index for arrays to access PIND/DDRD/PORTD and PCMSK2
#define D0_D7     2                 //!< Alias of COWPI_PD for corresponding to pins D0-D7 on the Arduino Uno & Arduino Nano

 
void setup() {
  pinMode(2, INPUT_PULLUP);
  pinMode(3, INPUT_PULLUP);
  pinMode(6, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);
  pinMode(10, INPUT_PULLUP);
  pinMode(12, INPUT_PULLUP);
  pinMode(15, INPUT_PULLUP);
  pinMode(17, INPUT_PULLUP);
 
  pinMode(13,OUTPUT);  // LED


  Serial.begin(9600);
  
  register_ISR(1L << 10, foo);
  register_ISR(1L << 15, foo);
  register_ISR(1L << 17, foo); // ??
  register_ISR(1L << 9, quux);
  register_ISR(1L << 12, bar);
  register_ISR(1L << 6, xyzzy);
  register_ISR(1L << 3, xyzzy);
  register_ISR(1L << 2, quux);
}
 
 
void loop() {
  // Nothing needed
}

void foo(void) {
  Serial.println("foo");
}

void bar(void) {
  Serial.println("bar");
}

void xyzzy(void) {
  Serial.println("xyzzy");
}

void quux(void) {
  Serial.println("quux");
}