To set 'N' bits in a number efficiently , N is a variable.

Question

Anonymous · Accepted Answer

Left shifting 1by N bits gives a power of 2 and if you subtract 1 from power of 2 you will N number of 1s.

Anonymous · Answer

MASK =  (1 << N) - 1;
number =  Number | MASK;

anonymous · Answer

why -1?

Anonymous · Answer

This is wrong.

If u take the number 111 and if you want to set 4 bits, then there will be no
bits set at all. The total number of SET bits in 111 will remain unchanged.

Number 111 = 1101111(in bit representation)
Now 4 set bits = (1<<4)-1 = 15

Now OR these two numbers. 111 | 15

in bit representation   1101111
                                              1111
                                       -------------
                                       1101111
                                      -------------

So we can see that we haven't SET any bit additional.

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