1. A method of computing at least a first and a second tree of arithmetic or logical operations on a microprocessor comprising at least n parallel processing elements to execute n arithmetic or logical operations in parallel, the computation of each tree requiring a plurality of successive iterations, the result of each iteration being used during the computation of the next iteration, where n is a positive integer greater than four, the method comprising: executing n arithmetic or logical operations of a first iteration of the first tree in parallel using the n processing elements, then executing m arithmetic or logical operations in parallel between the results of the first iteration, using m processing elements chosen from the n processing elements used for the computation of the first iteration, the other n-m processing element being unused for the computation of the second iteration, where m is an integer strictly smaller than n, wherein in parallel with the computation of the second iteration of the first tree, the method comprises executing k arithmetic or logical operations of the second tree in parallel using k processing elements chosen from the n-m processing elements unused for the computation of the second iteration of the first tree, where k is an integer smaller than or equal to n-m.