Machine Level Representation Homework

files.c

/* 3.55  */
long decode(long x, long y, long z) {
  long tmp = y - z;
  return (tmp * x) ^ (tmp << 63 >> 63);
}

/* 3.57 */
#include <stdio.h>
#include <assert.h>

long cread(long *xp) {
  return (xp ? *xp : 0);
}

long cread_alt(long *xp) {
  return (!xp ? 0 : *xp);
}

int main(int argc, char* argv[]) {
  long a = 0;
  assert(cread(&a) == cread_alt(&a));
  assert(cread(NULL) == cread_alt(NULL));
  return 0;
}

/* 3.58 */ 
/* Enumerated type creates set of contants numbered 0 and upward */
typedef enum { MODE_A, MODE_B, MODE_C, MODE_D, MODE_E } mode_t;

long switch3(long *p1, long *p2, mode_t action) {
  long result = 0;
  switch(action) {
    case MODE_A:
      result = *p2;
      *p2 = *p1;
      break;
    case MODE_B:
      *p1 = *p1 + *p2;
      result = *p1;
      break;
    case MODE_C:
      *p1 = 59;
      result = *p2;
      break;
    case MODE_D:
      *p1 = *p2;
      result = 27;
      break;
    case MODE_E:
      result = 27;
      break;
    default:
      result = 12;
      break;
  }
  return result;
}