Finish Data Lab

LAB2-datalab/datalab-handout/bits.c

@@ -228,16 +228,11 @@ int tmin(void)
  *   Max ops: 15
  *   Rating: 2
  */
-// int fitsBits(int x, int n)
-// {
-//   int moveBits = 33 + ~n;                   // Equals to 32-n
-//   int result = (x << moveBits) >> moveBits; // Left move, and then right move
-//   return !(x ^ result);                     // If okay, result should be equal to x
-// }
 int fitsBits(int x, int n)
 {
-  n = n + 31;
-  return !(((x >> n) + 1) >> 1);
+  int moveBits = 33 + ~n;                   // Equals to 32-n
+  int result = (x << moveBits) >> moveBits; // Left move, and then right move
+  return !(x ^ result);                     // If okay, result should be equal to x
 }
 
 /*
@@ -355,7 +350,40 @@ unsigned float_neg(unsigned uf)
  */
 unsigned float_i2f(int x)
 {
-  return 2;
+  int sign, exp = 0, frac = 0, i = 0;
+
+  if (x == 0) // Two special situations, cannot be calculated normally
+  {
+    return 0;
+  }
+  if (x == 0x80000000)
+  {
+    return 0xcf000000;
+  }
+
+  sign = (x >> 31) & 1; // Get the sign bit & abs(x)
+  if (sign)
+  {
+    x = -x;
+  }
+
+  i = 30; // Not 31 coz the top bit is always 0
+  while (!(x >> i))
+  {
+    i--;
+  }
+  exp = i + 127; // Get the exponent. i is the E, unbiased
+
+  x = x << (31 - i);          // Left shift to clean zeroes, right shift to fit 23 bits...
+  frac = (x >> 8) & 0x7fffff; // ...to get the fraction
+  x = x & 0xff;
+  frac += (x > 0x80) || ((x == 0x80) && (frac & 0x01)); // Round up if fraction is greater than 0.5
+  if (frac >> 23)
+  {
+    exp++;
+    frac = frac & 0x7fffff;
+  }
+  return (sign << 31) | (exp << 23) | frac;
 }
 /*
  * float_twice - Return bit-level equivalent of expression 2*f for
@@ -385,7 +413,7 @@ unsigned float_twice(unsigned uf)
   {
     return uf;
   }
-  // if ((exp >> 23) + 1 == 0xff) // exponent overflow
+  // if ((exp >> 23) + 1 == 0xff)
   if (exp == 0x7f000000) // exponent overflow
   {
     return sign | 0x7f800000;