tff.analytics.count_distinct.build_federated_secure_max_computation

Builds a tff.Computation for computing max in a secure fashion.

tff.analytics.count_distinct.build_federated_secure_max_computation() -> tff.Computation

Specifically, the returned computation consumes sketches at @CLIENTS and returns the element-wise max of the inpt sketches @SERVER.

Note: this returned computation assumes the values to be maxed are in the range [0, HLL_BIT_INDEX_TAIL+1]. This function works by onehot encoding the values which allows us to sum the values securely and then infer the max based on the non-zero entries of the sum. This approach is feasible because the inputs are small non-negative integers. Generalizations of this function would require communication proportional to (upper_bound - lower_bound).

Returns
A tff.Computation for computing max of client vectors.