Blum Micali PRG

Runner.java

public class Runner {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		//Generate the first 100 bits from Blum-Micali PRG with p = 34319, g = 4, and seed x = 1022
		
		long p = 34319;
		long g = 4;
		long x = 1022;
		long a;
		
		for(int i = 0; i < 100; i++){
			a = modExp(g, x, p);
			if(a > (p-1)/2)
				System.out.print("1");
			else
				System.out.print("0");
			x = a;
		}
	}
	
	public static long modExp(long g, long x, long p){
		long r = 1;
		
		while(x > 0){
			if(x % 2 == 1)
				r = r*g % p;
			x = (long)Math.floor((double)x/2);
			g = g*g % p;
		}
		return r;
	}
}

why its a>(p-1)/2 in line no. 15?