Elias Gamma Encoding in Python

The Elias gamma code is a universal code that is used to encode a sequence of positive integers. It is developed by Peter Elias. It is most useful when the upper-bound of integers cannot be determined beforehand.

Steps in Encoding:

To encode a number X,

  • Find the largest N, with
    2^{N}\leq X(greater power of 2).

  • Encode N using Unary coding(i.e N zeroes followed by a one).
  • Append the integer (X-2^{N}) using N digits in Binary.

Example: Let’s consider an example whwre we want to encode 10,
We can represent 10 as:
10=2^{3} + 2.
Step1: Here, largest N = 3
Step2: N(=3) in Unary followed by a one = 0001
Step3: Now Representation of 2 in Binary using N(=3) digits = 010
So, Elias gamma encoding of 10 = 0001010

Below is the implementation of the above approach.





# Python3 implementation
from math import log
log2 = lambda x: log(x, 2)
def Unary(x):
    return (x-1)*'0'+'1'
def Binary(x, l = 1):
    s = '{0:0%db}' % l
    return s.format(x)
def Elias_Gamma(x):
    if(x == 0): 
        return '0'
    n = 1 + int(log2(x))
    b = x - 2**(int(log2(x)))
    l = int(log2(x))
    return Unary(n) + Binary(b, l)



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