Bit Shifting

Introduction

• Bit Shifting is an operation which shifts bits.
• The bits within bytes can be shifted either left or right, by a specified amount.
• Bits maybe lost if their index is shifted outside the range of the integer.
• It is also referred to as 'bitwise shifting'.

Left Shifting

• When left shifting, we are adding 0's to the right edge of the integer, moving existing bits left to accomodate this.
• The left shift operator is <<.
• It is a binary operator:
  • its first parameter is the integer you want to shift,
  • the second parameter is the amount you want to shift by

Example

a      = 0011
a << 1 = 0110

Code (Python)

def print_bits(i):
    print(bin(i)[2:].zfill(4))


a = int('0011', 2)
print_bits(a) # prints '0011'

aShifted = a << 1
print_bits(aShifted) # prints '0110'

• In Python, the size of an integer is not fixed.
• and so bits are not lost no matter how much you shift by.
• In other languages where it is fixed, shifting a bit beyond the size of the integer will mean the bit is lost.

Right Shifting

• When right shifting, we are adding 0's to the left edge of the integer.
  • moving existing bits right to accomodate this.
• The right shift operator is >>
• It is also a binary operator:
  • its first parameter is the integer you want to shift,
  • and the second parameter is the amount you want to shift by

Example

a      = 0011
a >> 1 = 0001

Code (Python)

def print_bits(i):
    print(bin(i)[2:].zfill(4))

a = int('0011', 2)
print_bits(a) # prints '0011'

aShifted = a >> 1
print_bits(aShifted) # prints '0001'