finish quiz5-6

lab2/datalab-handout/bits.c

@@ -206,7 +206,9 @@ int allOddBits(int x) {
  *   Rating: 2
  */
 int negate(int x) {
-  return 2;
+  int notx = ~x;
+  int res = notx + 1;// since ~x + x = 1111...111 = -1, ~x + x + 1 = 0
+  return res;
 }
 //3
 /* 
@@ -219,7 +221,12 @@ int negate(int x) {
  *   Rating: 3
  */
 int isAsciiDigit(int x) {
-  return 2;
+  int neg0x3a = ~(0x3a) + 1;
+  int neg0x30 = ~(0x30) + 1;
+  int signofminus0x3a = (x + neg0x3a) >> 31; // should be all 1
+  int signofminus0x30 = (x + neg0x30) >> 31; // should be all 0
+  int res = !(signofminus0x30 | (~signofminus0x3a));
+  return res;
 }
 /* 
  * conditional - same as x ? y : z