// https://forum.arduino.cc/t/what-is-this-code-for-msbfirst-lsbfirst-bit-shifting-doing/1056898/6

// This version uses left and right shift of the 8-bit loop variable rather
// than a count value. This allows using the loop variable as a mask against
// the outgoing data and saves using a separate mask variable. This doesn't 
// realize any real advantage because the compiler adds a 16-bit loop counter
// anyway in addition to the shifted value.

// The code drives eight CC leds via a 74HC595 register.

const uint8_t clockPin = 2;
const uint8_t latchPin = 3;
const uint8_t dataPin = 4;
const uint8_t pButton = A0;
uint8_t pButtonLast;

const uint8_t lsbfirst = 1;

uint8_t number;

void setup() {
  Serial.begin(115200);
  pinMode(pButton, INPUT_PULLUP);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  digitalWrite(latchPin, LOW);
}

void loop() {
  // shift the loop variable and use it directly ( no bit shifting on the data variable )
  static byte button;

  number = random(255);
  button = digitalRead(pButton);

  if (button == LOW && pButtonLast == HIGH) {
    // shiftout(dataPin, clockPin, 1, number);
    shiftout(dataPin, clockPin, 0, number);
    Serial.println(number);
  }

  pButtonLast = button;
  delay(10);
}

void shiftout(uint8_t dataPin_, uint8_t clockPin_, uint8_t bitOrder, uint8_t val)
{
  byte i;
  digitalWrite(latchPin, LOW);

  if (bitOrder == lsbfirst) {
    for (i = 1; i != 0; i <<= 1) {
      digitalWrite(dataPin, (val & i) ? HIGH : LOW);
      digitalWrite(clockPin_, LOW);
      digitalWrite(clockPin_, HIGH);
    }
  }

  else
    for ( i = 128; i != 0; i >>= 1) {
      digitalWrite(dataPin, (val & i) ? HIGH : LOW);
      digitalWrite(clockPin_, LOW);
      digitalWrite(clockPin_, HIGH);
    }

  digitalWrite(latchPin, HIGH);
}