finish quiz10

lab2/datalab-handout/bits.c

@@ -143,8 +143,8 @@ NOTES:
  *   Rating: 1
  */
 int bitXor(int x, int y) {
-  int  p1 = ~x;
-  int  q1 = ~y;
+  int p1 = ~x;
+  int q1 = ~y;
   int a1 = x&y;
   int b1 = ~a1;
   int a2 = p1&q1;
@@ -293,7 +293,43 @@ int logicalNeg(int x) {
  *  Rating: 4
  */
 int howManyBits(int x) {
-  return 0;
+  int sign = x >> 31;//0x00 if postive, 0xffffffff if negative
+  int abseminus1 = (sign & (~x)) | ((~sign) & x); // x if x >= 0 , -x - 1 if x < 0
+
+  int rs16 = abseminus1 >> 16;
+  int bits16_flag = (!!(rs16) << 31) >> 31; // 0xfffffff if not 0
+  int bits16 = 16;
+  int rs16r = (bits16_flag & rs16) | ((~bits16_flag) & abseminus1); // rs16, if rs16 not 0, abseminus1 if rs16 0
+  int b16 = bits16_flag & bits16;
+
+  int rs8 = rs16r >> 8;
+  int bits8_flag = (!!(rs8) << 31) >> 31; // 0xfffffff if not 0
+  int bits8 = 8;
+  int rs8r = (bits8_flag & rs8) | ((~bits8_flag) & rs16r); // rs8, if rs8 not 0, rs16 if rs8 0
+  int b8 = bits8_flag & bits8;
+
+  int rs4 = rs8r >> 4;
+  int bits4_flag = (!!(rs4) << 31) >> 31; // 0xfffffff if not 0
+  int bits4 = 4;
+  int rs4r = (bits4_flag & rs4) | ((~bits4_flag) & rs8r); // rs4, if rs4 not 0, rs8 if rs4 0
+  int b4 = bits4_flag & bits4;
+
+  int rs2 = rs4r >> 2;
+  int bits2_flag = (!!(rs2) << 31) >> 31; // 0xfffffff if not 0
+  int bits2 = 2;
+  int rs2r = (bits2_flag & rs2) | ((~bits2_flag) & rs4r); // rs2, if rs2 not 0, rs4 if rs2 0
+  int b2 = bits2_flag & bits2;
+
+  int rs1 = rs2r >> 1;
+  int bits1_flag = (!!(rs1) << 31) >> 31; // 0xfffffff if not 0
+  int bits1 = 1;
+  int rs1r = (bits1_flag & rs1) | ((~bits1_flag) & rs2r); // rs1, if rs1 not 0, rs2 if rs1 0
+  int b1 = bits1_flag & bits1;
+
+  int is0orneg1 = (!(x ^ (0))) | (!(x ^((1<<31)>>31)));
+
+  int res = ((!is0orneg1 << 31 >> 31) & (b16 + b8 + b4 + b2 + b1 + 2)) | is0orneg1;
+  return res;
 }
 //float
 /*