/* C program for BCD / Integer conversions */

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

/* Function prototypes */

unsigned int  8 bcd2int(unsigned 4 *bcd);
 int int2bcd(int i, int bcd[]);

/****************************************************************************
/* main function
 ****************************************************************************/

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

	int i;									/* Store an integer value */
	int bcd[2];								/* Store a two-dogit BCD value */
											/* (MSD is bcd[1], LSD is bcd[0]) */
	int bcdcount[2] = { 0, 0 };				/* Stores two-digit BCD count */

	/* This loop tests the bcd2int and int2bcd functions */
	for (;;) {

		/* Convert bcdcount from BCD to integer */
		i = bcd2int(bcdcount);
		/* Convert integer back to BCD */
		int2bcd(i, bcd);

		/* Write out the results */
		printf("%d%d => %d => %d%d\n",
		       bcdcount[1], bcdcount[0], i, bcd[1], bcd[0]);

		/* Increment the BCD counter */
		if ( bcdcount[0]++ == 9 ) {
			bcdcount[0] = 0;
			if ( bcdcount[1]++ == 9 )
				break;
		}
	}

	/* This is the end of the program */
	exit (EXIT_SUCCESS);
}

/****************************************************************************
/* Convert a two-digit binary-coded decimal (BCD) number to an integer
 ****************************************************************************/

int bcd2int(int bcd[])
{
	return ( 10 * bcd[1] + bcd[0] );
}

/****************************************************************************
/* Convert an unsigned integer to a two-digit BCD number
 ****************************************************************************/

void int2bcd(int i, int bcd[2])

/* "i" is an unsigned integer, assumed to be less than 128 */

{
	int bit;								/* Loop variable - counts bits */
	int Carry;								/* Carry from BCD digit 0 to 1 */

	bcd[0] = 0;								/* Reset the BCD digits to 0 */
	bcd[1] = 0;

	for (bit = 0; bit < 8; bit++ ) {		/* Assume 8 bits */

		if ( bcd[0] < 5 ) {					/* Bottom BCD digit */
			bcd[0] *= 2;
			Carry = 0;
		}
		else {
			bcd[0] = (bcd[0] - 5) * 2;
			Carry = 1;
		}

		if ( i & 0x80 )						/* Add the top bit of i */
			bcd[0]++;						/* to the bottom BCD digit */
		i *= 2;								/* Shift i to the left */

		if ( bcd[1] < 5 ) {					/* Top BCD digit (no carry) */
			bcd[1] *= 2;
		}
		else {
			bcd[1] = (bcd[1] - 5) *2;
		}
		bcd[1] += Carry;

	}
}