It is very hard to multiply numbers d times. We can multiply numbers just $\theta \lg d$ times, using a technique known as repeated squaring.

Algorithms - Dasgupta, C. H. Papadimitriou, and U. V. Vazirani (2006)

Algorithms - Dasgupta, C. H. Papadimitriou, and U. V. Vazirani (2006)