#include<stdio.h>

bool givenStream[2000];

void ReadStream() {
        FILE *f = fopen("stream.txt","r");
        for(int i=0;!feof(f);i++)
        {
                givenStream[i] = fgetc(f)-'0';
                fgetc(f);
        }
        fclose(f);
}

// This gives you the last bit - so needs to be added to the stream of bits for a register
// Works by counting the number of bits, and if even, the last bit must be a 0, if odd it must be a 1 - so cnt counts the bits, then
// returning cnt mod 2 gives you the last bit
int countBitsMod2(int x) {
	int temp=x;
	int cnt=0;
	int pos;
	for(pos=0;pos<32;pos++) {
		if(temp%2==1) {
			cnt+=1;
		} else {
			cnt+=0;
		}
		temp=temp/2;
	}
	return cnt%2;
}


int shiftreg1(int r) {
	return (r >> 1) | (((r & 1) ^ ((r >> 6) & 1)) << 6);
}

int shiftreg2(int r) {
//	return (r>>1) | (((r&1)^((r>>9)&1))<<10);
	return (r >> 1) | (((r & 1) ^ ((r >> 9) & 1)) << 10);
}

int compareStream(int stream[]) {
	int matches;
	float matchPercentage;
	for(int i=0;i<2000;i++) {
		if(stream[i]==givenStream[i]) {
			matches++;
		}
	}
	matchPercentage = (float(matches)/2000)*100;
	if(matchPercentage>60) {
		printf("Correlation: %f\n",matchPercentage);
	}
	return 1;
}

int main() {
	// Reg 1, 50% (uncorrelated), tap seq=1,7
	// Reg 2, 75% correlation, tap seq=1,10
	// Reg 3, 75% correlation, tap seq=1,10,11,13
	int reg1length=128,reg2length=2048,reg3length=8192;
	int reg1,reg2,reg3;
	int reg1Output[2000],reg2Output[2000],reg3Output[2000];

	for(reg1=1;reg1<128;reg1++) {
		int tempReg1=reg1;
		for(int i=0;i<2000;i++) {
			reg1Output[i] = countBitsMod2(tempReg1);
			tempReg1 = shiftreg1(tempReg1);
		}
		compareStream(reg1Output);
	}	
	
	for(reg2=1;reg2<reg2length;reg2++) {
		int tempReg2=reg2;
		for(int i=0;i<2000;i++) {
			reg2Output[i]=countBitsMod2(tempReg2);
			tempReg2 = shiftreg2(tempReg2);
		}
		compareStream(reg2Output);
	}
}