Create elias.py

elias.py

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+"""
+Elias γ code or Elias gamma code is a universal code encoding positive integers.
+It is used most commonly when coding integers whose upper-bound cannot be determined beforehand.
+Elias δ code or Elias delta code is a universal code encoding the positive integers,
+that includes Elias γ code when calculating.
+Both were developed by Peter Elias.
+"""
+from math import log,ceil
+
+log2 = lambda x: log(x,2)
+
+# Calculates the binary number
+def binary(x,l=1):
+	fmt = '{0:0%db}' % l
+	return fmt.format(x)
+
+# Calculates the unary number
+def unary(x):
+	return (x-1)*'1'+'0'
+
+def elias_generic(lencoding, x):
+	"""
+	The compressed data is calculated in two parts. 
+	The first part is the unary number of 1 + ⌊log2(x)⌋. 
+	The second part is the binary number of x - 2^(⌊log2(x)⌋).
+	For the final result we add these two parts.
+	"""
+	if x == 0: return '0'
+
+	first_part = 1 + int(log2(x))
+
+	a = x - 2**(int(log2(x)))
+
+	k = int(log2(x))
+
+	return lencoding(first_part) + binary(a,k)
+
+def elias_gamma(x):
+	"""
+	For the first part we put the unary number of x.
+	"""
+	return elias_generic(unary, x)
+
+def elias_delta(x):
+	"""
+	For the first part we put the elias_g of the number.
+	"""
+	return elias_generic(elias_gamma,x)