#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define ERROR_15 (0.000000000000001)
#define ERROR_11 (0.00000000001)


int main(int argc, char *argv[]){

	int ret = 0;
	int stop = 0;
	FILE *f1 = NULL;
	FILE *f2 = NULL;
	long unsigned int line = 1;

	if(argc < 3){
		fprintf(stderr, "ERROR: Wrong usage.\n");
		fprintf(stderr, "Usage: %s <file1> <file2> [stop]\n", argv[0]);
		fprintf(stderr,
			"\tThis program compares 64 bit floating point numbers stored in a separate\n"
			"\tline each from <file1> and <file2>. If all the pairs of numbers are the\n"
			"\tsame up to the 15th decimal place, 0 will be returned. If not, this program\n"
			"\twill check if all numbers are the same up to the 11th decimal place, and\n"
			"\tif so 1 will be returned. If [stop] is 1, this program will stop as soon\n"
			"\tas this happens. If any numbers are not the same up to the 11th decimal\n"
			"\tplace, 2 will be returned. If [stop] is 2, this program will stop as soon\n"
			"\tas this happens. If there is an error while executing this program, -1 will\n"
			"\tbe returned, unless the error lies within the files' structures, in which\n"
			"\tcase 2 will be returned, as it means there was a significant difference in\n"
			"\tthe outputs. Compile with -DDEBUG (make debug) or define DEBUG in the program\n"
			"\tto print debug information.\n"
		);
		ret = -1;
		goto end;
	}

	if(argc > 3){
		stop = atoi(argv[3]);
	}

	f1 = fopen(argv[1], "rb");
	if(!f1){
		fprintf(stderr, "ERROR: Cannot open file '%s'.\n", argv[1]);
		ret = -1;
		goto end;
	}
	f2 = fopen(argv[2], "rb");
	if(!f2){
		fprintf(stderr, "ERROR: Cannot open file '%s'.\n", argv[2]);
		ret = -1;
		goto end;
	}

	while(!feof(f1) && !feof(f2)){
		double d1, d2;
	
		if(fscanf(f1, "%lg\n", &d1) != 1){
			fprintf(stderr, "ERROR: Cannot read number from file '%s' at line %lu.\n", argv[1], line);
			ret = 2;
			goto close_end;
		}
		if(fscanf(f2, "%lg\n", &d2) != 1){
			fprintf(stderr, "ERROR: Cannot read number from file '%s' at line %lu.\n", argv[1], line);
			ret = 2;
			goto close_end;
		}
		
		double error = fabs(d1-d2);
		if(error >= ERROR_15){
			if(error < ERROR_11){
				ret = 1;
			}else{
				ret = 2;
			}
			if(stop > 0 && stop == ret){
				goto close_end;
			}
		}
		line++;
	}

	if((feof(f1) && !feof(f2)) || (!feof(f1) && feof(f2))){
		fprintf(stderr, "ERROR: Different number of lines in files '%s' and '%s'.\n", argv[1], argv[2]);
		ret = 2;
	}

close_end:
	fclose(f1);
	fclose(f2);

end:
#ifdef DEBUG
	printf("%lu lines read\n", line);
	printf("Return value: %d\n", ret);
#endif

	return ret;
}