Unrolling the Recursion
Unrolling recursion involves expanding out the recursive calls into an iterative implementation. This eliminates function call overhead.
For example, recursive factorial:
factorial(n)
if n == 0:
return 1
else
return n * factorial(n1)
Can be unrolled into iteration:
factorial(n):
result = 1
for i = 1 to n:
result *= i
return result
Java example unrolling Fibonacci recursion:


C++ example unrolling binary search:


Python example unrolling power function:


Unrolling recursion removes function call overhead for improved performance.
Unrolling the recursion is an optimization technique used to make a recursive function more efficient by replacing it with an iterative version. This eliminates the overhead associated with recursive function calls, such as stack maintenance and function call overheads. This is particularly useful when the recursive calls are trivial or the recursive tree is shallow.
Java Code
Let’s consider calculating the factorial of a number using recursion and then unroll it.
Recursive Version


Unrolled Version


In the unrolled version, we use a for
loop to eliminate the recursive calls, thereby reducing the overhead.
C++ Code
Recursive Version


Unrolled Version


Here too, we replace the recursive function with a simple loop to calculate the factorial.
Python Code
Recursive Version


Unrolled Version


In Python, the concept remains the same. The recursive function is replaced by an iterative one to remove the overhead of recursive calls.
By unrolling the recursion, we not only make the code more efficient but also easier to understand and debug, without affecting the functionality.