PBS statistics

The shortint API now keeps track of how many PBS were executed with a global counter when enabling the pbs-stats feature.

This allows knowing precisely how many PBS are executed in a circuit and estimate the overall compute intensity of FHE code using either the shortint, integer or High-Level APIs.

You can query how many PBSes were executed by calling get_pbs_count. You can reset the PBS count by calling reset_pbs_count to more easily know how many PBSes were executed by each part of your code.

Combined with the debug mode it can allow to have estimations very quickly while iterating on the FHE code.

Here is an example of how to use the PBS counter:

use tfhe::prelude::*;
use tfhe::*;

pub fn main() {
    // Config and key generation
    let config = ConfigBuilder::default().build();

    let (cks, sks) = generate_keys(config);

    // Encryption
    let a = FheUint32::encrypt(42u32, &cks);
    let b = FheUint32::encrypt(16u32, &cks);

    // Set the server key
    set_server_key(sks);

    // Compute and get the PBS count for the 32 bits multiplication
    let c = &a * &b;
    let mul_32_count = get_pbs_count();

    // Reset the PBS count, and get the PBS count for a 32 bits bitwise AND
    reset_pbs_count();
    let d = &a & &b;
    let and_32_count = get_pbs_count();

    // Display the result
    println!("mul_32_count: {mul_32_count}");
    println!("and_32_count: {and_32_count}");
}