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use crate::shortint::atomic_pattern::AtomicPattern;
use crate::shortint::server_key::GenericServerKey;
use crate::shortint::Ciphertext;
impl<AP: AtomicPattern> GenericServerKey<AP> {
/// Compute a division between two ciphertexts.
///
/// The result is returned in a _new_ ciphertext.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// This function, like all "default" operations (i.e. not smart, checked or unchecked), will
/// check that the input ciphertext carries are empty and clears them if it's not the case and
/// the operation requires it. It outputs a ciphertext whose carry is always empty.
///
/// This means that when using only "default" operations, a given operation (like add for
/// example) has always the same performance characteristics from one call to another and
/// guarantees correctness by pre-emptively clearing carries of output ciphertexts.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let ct_1 = cks.encrypt(clear_1);
/// let ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// let ct_res = sks.div(&ct_1, &ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_res);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn div(&self, ct_left: &Ciphertext, ct_right: &Ciphertext) -> Ciphertext {
let mut ct_res = ct_left.clone();
self.div_assign(&mut ct_res, ct_right);
ct_res
}
/// Compute a division between two ciphertexts.
///
/// The result is returned in a _new_ ciphertext.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// This function, like all "default" operations (i.e. not smart, checked or unchecked), will
/// check that the input ciphertext carries are empty and clears them if it's not the case and
/// the operation requires it. It outputs a ciphertext whose carry is always empty.
///
/// This means that when using only "default" operations, a given operation (like add for
/// example) has always the same performance characteristics from one call to another and
/// guarantees correctness by pre-emptively clearing carries of output ciphertexts.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
/// let ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// sks.div_assign(&mut ct_1, &ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_1);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn div_assign(&self, ct_left: &mut Ciphertext, ct_right: &Ciphertext) {
let tmp_rhs: Ciphertext;
if !ct_left.carry_is_empty() {
self.message_extract_assign(ct_left);
}
let rhs = if ct_right.carry_is_empty() {
ct_right
} else {
tmp_rhs = self.message_extract(ct_right);
&tmp_rhs
};
self.unchecked_div_assign(ct_left, rhs);
}
/// Compute a division between two ciphertexts without checks.
///
/// The result is returned in a _new_ ciphertext.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let ct_1 = cks.encrypt(clear_1);
/// let ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// let ct_res = sks.unchecked_div(&ct_1, &ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_res);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn unchecked_div(&self, ct_left: &Ciphertext, ct_right: &Ciphertext) -> Ciphertext {
let mut result = ct_left.clone();
self.unchecked_div_assign(&mut result, ct_right);
result
}
/// Compute a division between two ciphertexts without checks.
///
/// The result is _assigned_ in `ct_left`.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
/// let ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// sks.unchecked_div_assign(&mut ct_1, &ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_1);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn unchecked_div_assign(&self, ct_left: &mut Ciphertext, ct_right: &Ciphertext) {
let value_on_div_by_zero = ct_left.message_modulus.0 - 1;
self.unchecked_evaluate_bivariate_function_assign(ct_left, ct_right, |x, y| {
safe_division(x, y, value_on_div_by_zero)
});
}
/// Compute a division between two ciphertexts.
///
/// The result is returned in a _new_ ciphertext.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 1;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
/// let mut ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// let ct_res = sks.smart_div(&mut ct_1, &mut ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_res);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn smart_div(&self, ct_left: &mut Ciphertext, ct_right: &mut Ciphertext) -> Ciphertext {
let value_on_div_by_zero = ct_left.message_modulus.0 - 1;
self.smart_evaluate_bivariate_function(ct_left, ct_right, |x, y| {
safe_division(x, y, value_on_div_by_zero)
})
}
/// Compute a division between two ciphertexts without checks.
///
/// The result is _assigned_ in `ct_left`.
///
/// # Warning
///
/// /!\ A division by zero returns the input ciphertext maximum message value! For 2 bits of
/// message it will therefore return 3.
///
/// # Example
///
///```rust
/// use tfhe::shortint::gen_keys;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS;
///
/// // Generate the client key and the server key
/// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2_KS_PBS);
///
/// let clear_1 = 3;
/// let clear_2 = 2;
///
/// // Encrypt two messages
/// let mut ct_1 = cks.encrypt(clear_1);
/// let ct_2 = cks.encrypt(clear_2);
///
/// // Compute homomorphically a multiplication
/// sks.unchecked_div_assign(&mut ct_1, &ct_2);
///
/// // Decrypt
/// let res = cks.decrypt(&ct_1);
/// assert_eq!(clear_1 / clear_2, res);
/// ```
pub fn smart_div_assign(&self, ct_left: &mut Ciphertext, ct_right: &mut Ciphertext) {
let value_on_div_by_zero = ct_left.message_modulus.0 - 1;
self.smart_evaluate_bivariate_function_assign(ct_left, ct_right, |x, y| {
safe_division(x, y, value_on_div_by_zero)
});
}
}
// Specific division function returning value_on_div_by_zero in case of a division by 0
pub(crate) fn safe_division(x: u64, y: u64, value_on_div_by_zero: u64) -> u64 {
if y == 0 {
value_on_div_by_zero
} else {
x / y
}
}