7 segment with bits

int A = 7;
int B = 8;
int C = 9;
int D = 10;
int E = 11;
int F = 12;
int G = 13;

byte digits[] = {126, 48, 109, 121, 51,
                 91, 95, 112, 127, 123};

void setup()
{
    for (int i=A; i<=G; i++)
    {
        pinMode(i, OUTPUT);
    }
}

void loop()
{
    // countdown
    for (int i=9; i>=0; i--)
    {
        displayDigit(i);
        delay(1000);
    }
}

void displayDigit(int d)
{
    int mask = 64;
    for (int segment = A; segment <= G; segment++)
    {
        digitalWrite(segment, digits[d] & mask);
        mask = mask >> 1;
    }
}