PBS statistics

This document explains how to use the PBS statistics feature in TFHE-rs' shortint API to assess the overall computational intensity in FHE applications.

The shortint API now includes a global counter to track the number of Programmable Bootstrapping (PBS) executed with the pbs-stats feature. This feature enables precise tracking of PBS executions in a circuit. It helps to estimate the overall compute intensity of FHE code using either the shortint, integer, or High-Level APIs.

To know how many PBSes were executed, call get_pbs_count. To reset the PBS count, call reset_pbs_count. You can combine two functions to understand how many PBSes were executed in each part of your code.

When combined with the debug mode, this feature allows for quick estimations during iterations 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}");
}