3 ms·

Could explain the << calculation a bit? I read about the operator but it’s not clear how this works

• schoen 2y ago
  It means "left shift" in binary. This corresponds to adding a specified number of zeros at the end of the binary representation of the original number. So 1 << 0 is binary 1, 1 << 1 is binary 10, 1 << 2 is binary 100, 1 << 3 is binary 1000... If you think about the meaning of place value in binary, this is exactly the same as raising two to a specified power. Each time you shift one place further left in binary, it's equivalent to multiplying the existing number by two. So repeating that a specified number of times is multiplying by a specified power of two.
• pansa2 2y ago
  Shifting an integer left `n` bits is equivalent to multiplying it by `2 ** n`
• nanis 2y ago
  1 is 2 to the power 0 ... 0b0001 shifted left once, it becomes 2 to the power 1 ... 0b0010 shifted left twice, it becomes 2 to the power 2 ... 0b0100 shifted left three times, it becomes 2 to the power 3 ... 0b1000 etc until shifted left 136_279_841 times, it becomes 2 to the power 136_279_84 ... 0b1000...many zeros...0000 subtract 1, it becomes 0b0111...many ones...1111
  • schoen 2y ago
    One funny thing about Mersenne primes is that, as a result of what you describe, they are exactly those primes whose binary representation consists of a prime number of ones! The smallest Mersenne prime, three, is binary 11, while the next largest is seven (111), then 31 (11111), then 127 (1111111). The next candidate, 2047 (11111111111), is not prime.