Integer#bit_length

bit_length → integer

# File tmp/rubies/ruby-3.3.0/numeric.rb, line 160
def bit_length
  Primitive.attr! :leaf
  Primitive.cexpr! 'rb_int_bit_length(self)'
end

Returns the number of bits of the value of self, which is the bit position of the highest-order bit that is different from the sign bit (where the least significant bit has bit position 1). If there is no such bit (zero or minus one), returns zero.

This method returns ceil(log2(self < 0 ? -self : self + 1))>.

Example

(-2**1000-1).bit_length   # => 1001
(-2**1000).bit_length     # => 1000
(-2**1000+1).bit_length   # => 1000
(-2**12-1).bit_length     # => 13
(-2**12).bit_length       # => 12
(-2**12+1).bit_length     # => 12
-0x101.bit_length         # => 9
-0x100.bit_length         # => 8
-0xff.bit_length          # => 8
-2.bit_length             # => 1
-1.bit_length             # => 0
0.bit_length              # => 0
1.bit_length              # => 1
0xff.bit_length           # => 8
0x100.bit_length          # => 9
(2**12-1).bit_length      # => 12
(2**12).bit_length        # => 13
(2**12+1).bit_length      # => 13
(2**1000-1).bit_length    # => 1000
(2**1000).bit_length      # => 1001
(2**1000+1).bit_length    # => 1001

For Integer n, this method can be used to detect overflow in Array#pack:

Example

if n.bit_length < 32
  [n].pack('l') # No overflow.
else
  raise 'Overflow'
end

See also #anybits? #ceil #allbits? #ceildiv also in 4.1 · 4.0 · 3.4 · 3.2 · 3.1 · 3.0

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