CODEWITHSUNDEEP
rubybit-manipulation
Zenith19
Zenith19

Reputation: 65

Flipping bits without getting negative number

How can I flip the bits of an integer without changing its sign? For example, how can I flip "1010" (1010) to "0101" (510)?

Bitwise negative operator results in negative number: ~10 (~0b1010) → -11 (0b0101).

Upvotes: 4

Views: 904

Answers (3)

sawa
sawa

Reputation: 168199

If you mean strings, then:

"1010".tr("01", "10") # => "0101"

If you mean numbers, then:

10.to_s(2).tr("01", "10").to_i(2) # => 5

Upvotes: 2

Rustam Gasanov
Rustam Gasanov

Reputation: 15791

I am not sure if it fits for your needs, but you can just flip binary string char by char like this:

"1010".chars.map { |i| i == "1" ? "0" : "1" }.join #=> "0101"

Upd:

How about this:

a = ~10
(a.bit_length - 1).downto(0).map { |i| a[i] }.join #=> "0101"

Upvotes: 1

Stefan
Stefan

Reputation: 114208

You can flip the bits via XOR:

    1010 (decimal 10)
XOR 1111 (decimal 15)
  = 0101 (decimal 5)

In Ruby:

0b1010 ^ 0b1111 #=> 5

The number of 1's corresponds to the number of bits, therefore you could use:

num  = 0b1010
num ^ (1 << num.bit_length) - 1
#=> 5

Upvotes: 13

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