代码清单1-6
#define HALF_BITS_LENGTH 4
#define FULLMASK 255
#define LMASK (FULLMASK << HALF_BITS_LENGTH)
#define RMASK (FULLMASK >> HALF_BITS_LENGTH)
#define RSET(b, n) (b = ((LMASK & b) ^ n))
#define LSET(b, n) (b = ((RMASK & b) ^ (n << HALF_BITS_LENGTH)))
#define RGET(b) (RMASK & b)
#define LGET(b) ((LMASK & b) >> HALF_BITS_LENGTH)
#define GRIDW 3
#include <stdio.h>
#define HALF_BITS_LENGTH 4
#define FULLMASK 255
#define LMASK (FULLMASK << HALF_BITS_LENGTH)
#define RMASK (FULLMASK >> HALF_BITS_LENGTH)
#define RSET(b, n) (b = ((LMASK & b) ^ n))
#define LSET(b, n) (b = ((RMASK & b) ^ (n << HALF_BITS_LENGTH)))
#define RGET(b) (RMASK & b)
#define LGET(b) ((LMASK & b) >> HALF_BITS_LENGTH)
#define GRIDW 3
int main()
{
unsigned char b;
for(LSET(b, 1); LGET(b) <= GRIDW * GRIDW; LSET(b, (LGET(b) + 1)))
for(RSET(b, 1); RGET(b) <= GRIDW * GRIDW; RSET(b, (RGET(b) + 1)))
if(LGET(b) % GRIDW != RGET(b) % GRIDW)
printf("A = %d, B = %d\n", LGET(b), RGET(b));
return 0;
}