Please explain the meaning of the above line, and in particular, why such an iteration "t = t / 2" is used. Line highlighted red PS If possible, advise the literature so that more such silly questions do not arise :)

  • As I understand it, this is Herbert Shildt? - Vennic
  • Welcome to stack overflow in Russian! text information is better to attach as text: a) easier to read; b) can be copied; c) the search works. You can correct the question text by clicking below to edit the question text - aleksandr barakin
  • Yes, absolutely for a long time, I was thinking of starting either from Serie and Bates studying java or from a shieldt, I came to the conclusion that a shieldt is better - DD DD

2 answers 2

In short, this operation shifts the unit bit in the mask one position to the right.
Equivalent records:

t >> 1

If more, then the number 128 in binary number system:

 10000000

If 128 is divided in half, we get 64, which is in binary notation:

 01000000

32 will match:

 00100000

And so on, the single bit will move to the most rightmost position.

What is it for?

The fact is that the loop uses bitwise & , and at each iteration we sequentially get a bit from the variable val . As a result, if a positive number is obtained, then there is a one in this position, otherwise 0. If you don’t understand why this is the case, I recommend reading how bitwise operations work

  • Thank you, your answer helped me to understand, but you could not advise me what to read to understand the number systems, otherwise you can say that I began to study Java from scratch, that is, without any knowledge of computer science - DD DD
  • @ DDD I cannot advise any specific literature, but there are enough resources on the Internet on which the topic of number systems is revealed (definitions, translation from one to another, arithmetic, etc.). I would like to note that this is a common basic theme, not tied specifically to the Java programming language. I would advise you now to develop without a specific link to PL, and to gain knowledge in the field of computer science in general. For example, move towards data structures and algorithms. Programming languages ​​are born and die, and data structures and algorithms have been used for decades. - Roman Danilov
  • Only t >> 2 is divided by 4, and in half it is t >> 1 - avp
  • @avp, yes, indeed, corrected a slip of the pen - Roman Danilov

Because the binary number system is a power of two. Pay attention to the bitwise operation &, you can paint this cycle as:

 // 0 1 1 1 1 0 1 1 // 1 0 0 0 0 0 0 0 (128) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 0 0 0 0 0 0 // 0 1 0 0 0 0 0 0 (64) // & // 0 1 1 1 1 0 1 1 (123) // 0 1 0 0 0 0 0 0 1 // 0 0 1 0 0 0 0 0 (32) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 1 0 0 0 0 0 1 // 0 0 0 1 0 0 0 0 (16) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 1 0 0 1 0 1 // 0 0 0 0 1 0 0 0 (8) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 0 1 0 0 0 1 // 0 0 0 0 0 1 0 0 (4) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 0 0 0 0 0 0 // 0 0 0 0 0 0 1 0 (2) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 0 0 0 1 0 1 // 0 0 0 0 0 0 0 1 (1) // & // 0 1 1 1 1 0 1 1 (123) // 0 0 0 0 0 0 0 1 1

So for the transfer back you will need to do the following:

 0 1 1 1 1 0 1 1 (0*2^7) + (1*2^6) + (1*2^5) + (1*2^4) + (1*2^3) + (0*2^2) + (1*2^1) + (1*2^0) 0 + 64 + 32 + 16 + 8 + 0 + 2 + 1 = 123