An average case efficient algorithm for solving two variable linear diophantine equations

Solving two variable linear diophantine equations has applications in many cryptographic protocols such as RSA and Elliptic curve cryptography. Extended euclid's algorithm is the most widely used algorithm to solve these equations. We revisit two algorithms to solve two variable linear diophantine equations. For one of them, we do fine-grained analysis of the number of recursive calls and find a periodic function, which represents the number of recursive calls. We find the period and use it to derive an accurate closed form expression for the average number of recursive calls incurred by that algorithm. In the process of this derivation we get an upper bound on the average number of recursive calls, which depends on the intermediate values observed during the execution of algorithm. We propose an iterative version of the algorithm. While implementation of our algorithm, we verify a well known result from number theory about the probability of two random integers being coprime. Due to that result, our algorithm encounters an additional constraint for approximately 40% times. On almost all of these constrained inputs i.e. on nearly 100 % of them the algorithm outperforms two existing algorithms.