Question

I have the following Java code:

long a = Long.parseLong("11001100", 2);
long b = Long.parseLong("11000000", 2);
int npos = 0 ;
int pos = 0 ;
long n = ~(a ^ b) ;
int cnt = 0;
while (n != 0) {
  pos++ ;
  if ((n & 3) == 3) cnt++; // count how many matches
  else{
    npos = pos ;  // position that not matched also giving wrong which should be 2 nd position.
  }
  n >>>= 2;
}

System.out.println(npos + "  " + cnt) ; // also print which two bits are not matched i.e. 00 and 11

I am trying to find how many two-bit sequences match in two integers. I want also to find which two bits are not matched. Can anybody help me how to do that?

PS: I don’t have the string in my original code, only have integers. Therefore, I can’t do string manipulation.

Edit:

long a = Long.parseLong("11000100", 2);
long b = Long.parseLong("11000000", 2);
long mask = 0x03;
int npos = 0 ;
int cnt = 0;
long p1 = 0;
long p2 = 0;
for (int pos = 0; pos < 64; pos++, mask <<= 2) {

  if ((a & mask) == (b & mask)) {
     cnt++; // count how many matches
  } else {
    npos = pos ;  // *last* position that did not match
    p1 = (a & mask) ; // two bits that not matched
    p2 = (b & mask) ; // two bits that not matched
  }
}

  System.out.println(npos + "  " + cnt + " " + p1 + " " + p2) ; // also print which two bits are not matched i.e. 00 and 01

Answer 1

You parse the integers as base-10 numbers, where you probably wanted to parse them as binary integers, to do that use the method that has a radix parameter:

long a = Long.parseInt("11001100", 2);
long b = Long.parseInt("11000000", 2);

It might be easier to just run a loop comparing the 2 values using a mask:

long mask = 0x03;
int npos = 0 ;
int cnt = 0;

for (int pos = 0; pos < 32; pos++, mask <<= 2) {

  if ((a & mask) == (b & mask)) {
     cnt++; // count how many matches
  } else {
    npos = pos ;  // *last* position that did not match
  }
}