#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>

int
flipbit(unsigned long num, int pos, int onoff);
int
tellbit(unsigned long num, int pos, int onoff);
void
usage(int argc, char ** argv);
void
printbits(unsigned long);

int
main(int argc, char ** argv)
{
	char ch;
	int tellbits = 0;
	unsigned long num = 0;

	while ((ch = getopt(argc, argv, "tx:d:h?")) != EOF)
		switch (ch)
		{
			case 'x':
				sscanf(optarg,"%x", &num);
				break;
			case 'd':
				num = atol(optarg);
				break;
			case 't':
				tellbits = 1;
				break;
			case 'h':
			case '?':
			default:
				usage(argc, argv);
				break;
		}
			

		
					


	if(optind < argc && !num)
		num = atol(argv[optind]);

		
	while(1)
	{
		int instate;
		int pos;
		char buf[1024];
		size_t buflen = sizeof(buf);
		size_t retlen = 0;

		pos = 0;	

		printf("Decimal: %#0d Hex: %#0x \n", num, num);
		if(tellbits)
			printbits(num);

		printf("Bit position to turn off? ");
		if(!fgets(buf, buflen, stdin))
			break;
		if(EOF == sscanf(buf,"%d", &pos))
			instate = 0;
		else
		{
			instate = 1;
			num = flipbit(num, pos, 0);
		}
		
		printf("Bit position to turn on? ");
		if(!fgets(buf, buflen, stdin))
			break;
		if(EOF == sscanf(buf,"%d", &pos))
			instate = 0;
		else
		{
			instate = 1;
			num = flipbit(num, pos, 1);
		}

		printf("Value of bit position? ");
		if(!fgets(buf, buflen, stdin))
			break;
		if(EOF == sscanf(buf,"%d", &pos))
		{
			if(!instate)
				break;
		}
		else
			printf("Bit position %d is %s\n", pos, tellbit(num, pos, 1) ? "on" : "off");
	
	}
       	

}

int
flipbit(unsigned long num, int pos, int onoff)
{
	unsigned long tempnum = 1;
/*
	if(pos < 0 || pos > 31)
		return num;
*/	
	tempnum <<= pos;

	if(onoff)
	{
		num |= tempnum;
	}
	else
	{
		num &= ~tempnum;
	}
	return num;
		
}

int
tellbit(unsigned long num, int pos, int onoff)
{
	unsigned long tempnum = 1;
/*
	if(pos < 0 || pos > 31)
		return num;
*/	
	tempnum <<= pos;

	if(onoff)
		return(num & tempnum);
	else
		return(!(num & tempnum));
		
}

void
usage(int argc, char ** argv)
{
	fprintf(stderr,
	"Usage: %s [-t] [-x 0xnumber] [-d number] [-h | -?]\n"
	"	-t		: tell all bit positions\n"
	"	-x 0xNumber	: Hex number\n"
	"	-d number	: Decimal number\n"
	"	-h -?		: This message\n"
	,
	 "flipbit.exe"
	);
}	
	

void printbits(unsigned long num)
{
	int i;
	int j = 0;

	i = sizeof(num) * 8 + 1;

	while(--i)
		j += printf("|%d",i);

	printf("|\n");
	j++;

	while(--j)
		printf("-");
	printf("\n");
	

	i = sizeof(num) * 8 + 1;
	while(--i)	
	{
//		printf("Bit position %d is %s\n", i, tellbit(num, i, 1) ? "on" : "off");
		printf("|%d",tellbit(num,i,1) > 0 );
	}
	printf("|\n");
}