Chapter 2.3, Problem 2.43PP

Practice Problem 2.43 (solution page 157)

In the following code, we have omitted the definitions of constants M and N:

#define M /* Mystery number 1 */

#define N /* Mystery number 2 */

int arith(int x, int y) {

int result = 0;

result = x*M + y/N; /* M and N are mystery numbers. */

return result;

}

We compiled this code for particular values of M and N. The compiler optimized the multiplication and division using the methods we have discussed. The following is a translation of the generated machine code back into C:

/* Translation of assembly code for axith */

int optarith(int x, int y) {

int t = x;

x <<= 5;

x -= t;

if (y < 0) y + = 7;

y >> 3; /* Arithmetic shift */

return x+y;

}

What are the values of M and N?