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. The method comprises: a) executing (in 48) n arithmetic or logical operations of a first iteration of the first tree in parallel using the n processing elements, then b) executing (in 66) m arithmetic or logical operations in parallel between the results of the first iteration, using m processing elements chosen from the n processing element used for the computation of the first iteration, the other n−m processing element being unused for the computation of the second iteration. In parallel with the computation of the second iteration of the first tree, the method comprises executing (in 66) 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.