#include <stdio.h>
#include <stdlib.h>
#define X22             0x00400000   /* vector representation of X^{22} */
#define X11             0x00000800   /* vector representation of X^{11} */
#define MASK12          0xfffff800   /* auxiliary vector for testing */
#define GENPOL          0x00000c75   /* generator polinomial, g(x) */

long get_syndrome(long pattern) {
/*
 * Compute the syndrome corresponding to the given pattern, i.e., the
 * remainder after dividing the pattern (when considering it as the vector
 * representation of a polynomial) by the generator polynomial, GENPOL.
 * In the program this pattern has several meanings: (1) pattern = infomation
 * bits, when constructing the encoding table; (2) pattern = error pattern,
 * when constructing the decoding table; and (3) pattern = received vector, to
 * obtain its syndrome in decoding.
 */
    long aux = X22, aux2;
 
		if (pattern >= X11) {
       while (pattern & MASK12) {
					 while (!(aux & pattern)) aux = aux >> 1;
           pattern ^= (aux/X11) * GENPOL;
			 }
		}
    return(pattern);
}

void main (void) {
	unsigned long code;
	printf("Enter the 23-bit codeword in hexadecimal format: ");
	scanf("%lx", &code);
	code = ((code & 0xfff) << 11) | (code >> 12);
	printf("The syndrome is %0lx\n", get_syndrome(code));
}