CODEWITHSUNDEEP
java
Arpssss
Arpssss

Reputation: 3858

Java Finding Set Bits of Long

I have a long number. Now what I want is following (given in pseudo code) ,

for each two bits of that long

if the two bits == 11

then count++

(for example if number is "11 01 10 00 11" it will give count = 2)

Can anybody help me how to do this efficiently in Java ?

Upvotes: 1

Views: 108

Answers (1)

Marko Topolnik
Marko Topolnik

Reputation: 200168

public static int count11(long n) {
  int cnt = 0;
  while (n != 0) {
    if ((n & 3) == 3) cnt++;
    n >>>= 2;
  }
  return cnt;
}

The even more efficient variant:

public static int count11(long n) {
  int cnt = 0;
  while (n != 0) {
    switch ((int)(n & 0x3F)) {
    case 0x3F: cnt += 3; break;
    case 0x3C: case 0x33: case 0xF: cnt += 2; break;
    case 0x30: case 0xC: case 3: cnt++;
    }
    n >>>= 6;
  }
  return cnt;
}

Upvotes: 2

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