#include <stdlib.h>
#include <stdio.h>
#include <inttypes.h>
#include <stddef.h>

// x^16 + x^15 + x^13 + x^1 + 1 -- D4 LFSR
// 0, 7, 12, 14 works for 16-bits
// 1, 12, 14, 15 works for 16-bits
// 16,14,13,11
// 0, 12, 14, 15 works for 15-bits
// 31, 9, 7, 6, 3, 2
// 29, 28, 25, 24, 22, 0
// 0x8000019F

void createGnuplot(int tap1, int tap2, int tap3, int tap4) {
	char buf[1] = " ";
	FILE *template = fopen("plottemplate", "r");
	FILE *plotout = fopen("plot", "w");
	if(template == NULL || plotout == NULL) {
		return;
	}
	while(1) {
		*buf = fgetc(template);
		if (*buf == EOF) {
			fflush(plotout);
			break;
		}
		if(*buf == '$') {
			fprintf(plotout, "%d, %d, %d, %d", tap1, tap2, tap3, tap4);
		} else {
			fputc(*buf, plotout);
		}
	}
	fclose(template);
	fclose(plotout);

	return;
}

int main(int argc, char **argv) {
	uint16_t startState = 0x0005;
	uint16_t lfsr = startState;
	uint16_t bit;
	uint32_t count = 0;
	char *c;
	int tap1, tap2, tap3, tap4;


	if(argc == 5) {
		tap1 = strtol(argv[1], NULL, 10);
		tap2 = strtol(argv[2], NULL, 10);
		tap3 = strtol(argv[3], NULL, 10);
		tap4 = strtol(argv[4], NULL, 10);
	} else {
		tap1 = 15;
		tap2 = 4;
		tap3 = 2;
		tap4 = 1;
	}
	//printf("Initial state: %0x\n", lfsr);

	do {
		bit = ((lfsr >> tap1) ^ (lfsr >> tap2) ^ (lfsr >> tap3) ^ (lfsr >> tap4));
		lfsr = (lfsr >> 1) | (bit << 15);
		count++;
		//count % 100000000 == 0 ? printf("0x%08x\t%032b\n", lfsr, lfsr) : 0; // comment this line for speed check
        printf("%d\n", lfsr);
        // *c = scanf("%s");
	} while(lfsr != startState && count < 70000); //while(lfsr != startState);
	//printf("Final count: %u\n", count);
	createGnuplot(tap1, tap2, tap3, tap4);

	return 0;
}