Comparison operations

This document details the comparison operations supported by TFHE-rs.

Homomorphic integers support comparison operations. However, due to Rust's limitations, you cannot overload comparison symbols. This is because Rust requires Boolean outputs from such operations, but homomorphic types return ciphertexts. Therefore, you should use the following methods, which conform to the naming conventions of Rust’s standard traits:

• PartialOrd

• PartialEq

Supported operations:

name	symbol	type
Equal	eq	Binary
Not Equal	ne	Binary
Greater Than	gt	Binary
Greater or Equal	ge	Binary
Lower	lt	Binary
Lower or Equal	le	Binary

The following example shows how to perform comparison operations:

use tfhe::prelude::*;
use tfhe::{generate_keys, set_server_key, ConfigBuilder, FheInt8};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::default().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);

    let clear_a: i8 = -121;
    let clear_b: i8 = 87;

    let a = FheInt8::try_encrypt(clear_a, &keys)?;
    let b = FheInt8::try_encrypt(clear_b, &keys)?;

    let greater = a.gt(&b);
    let greater_or_equal = a.ge(&b);
    let lower = a.lt(&b);
    let lower_or_equal = a.le(&b);
    let equal = a.eq(&b);

    let dec_gt = greater.decrypt(&keys);
    let dec_ge = greater_or_equal.decrypt(&keys);
    let dec_lt = lower.decrypt(&keys);
    let dec_le = lower_or_equal.decrypt(&keys);
    let dec_eq = equal.decrypt(&keys);

    assert_eq!(dec_gt, clear_a > clear_b);
    assert_eq!(dec_ge, clear_a >= clear_b);
    assert_eq!(dec_lt, clear_a < clear_b);
    assert_eq!(dec_le, clear_a <= clear_b);
    assert_eq!(dec_eq, clear_a == clear_b);

    Ok(())
}