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use crate::integer::block_decomposition::{BlockDecomposer, DecomposableInto};
use crate::integer::ciphertext::IntegerRadixCiphertext;
use crate::integer::server_key::CheckError;
use crate::integer::ServerKey;
use crate::shortint::ciphertext::{Degree, MaxDegree};
use crate::shortint::{CarryModulus, MessageModulus};
impl ServerKey {
/// Computes homomorphically an addition between a scalar and a ciphertext.
///
/// This function computes the operation without checking if it exceeds the capacity of the
/// ciphertext.
///
/// The result is returned as a new ciphertext.
///
/// # Example
///
/// ```rust
/// use tfhe::integer::gen_keys_radix;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
///
/// // We have 4 * 2 = 8 bits of message
/// let size = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, size);
///
/// let msg = 4;
/// let scalar = 40;
///
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically an addition:
/// let ct_res = sks.unchecked_scalar_add(&ct, scalar);
///
/// // Decrypt:
/// let dec: u64 = cks.decrypt(&ct_res);
/// assert_eq!(msg + scalar, dec);
/// ```
pub fn unchecked_scalar_add<T, C>(&self, ct: &C, scalar: T) -> C
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
let mut result = ct.clone();
self.unchecked_scalar_add_assign(&mut result, scalar);
result
}
/// Computes homomorphically an addition between a scalar and a ciphertext.
///
/// This function computes the operation without checking if it exceeds the capacity of the
/// ciphertext.
///
/// The result is assigned to the `ct_left` ciphertext.
pub fn unchecked_scalar_add_assign<T, C>(&self, ct: &mut C, scalar: T)
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
let bits_in_message = self.key.message_modulus.0.ilog2();
let decomposer =
BlockDecomposer::with_early_stop_at_zero(scalar, bits_in_message).iter_as::<u8>();
for (ciphertext_block, scalar_block) in ct.blocks_mut().iter_mut().zip(decomposer) {
self.key
.unchecked_scalar_add_assign(ciphertext_block, scalar_block);
}
}
/// Verifies if a scalar can be added to a ciphertext.
///
/// # Example
///
///```rust
/// use tfhe::integer::gen_keys_radix;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
///
/// // We have 4 * 2 = 8 bits of message
/// let size = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, size);
///
/// let msg = 2u64;
/// let scalar = 40;
///
/// // Encrypt two messages:
/// let ct1 = cks.encrypt(msg);
///
/// // Check if we can perform an addition
/// sks.is_scalar_add_possible(&ct1, scalar).unwrap();
/// ```
pub fn is_scalar_add_possible<T, C>(&self, ct: &C, scalar: T) -> Result<(), CheckError>
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
let block_metadata_iter = ct
.blocks()
.iter()
.map(|b| (b.degree, b.message_modulus, b.carry_modulus));
self.is_scalar_add_possible_impl(block_metadata_iter, scalar)
}
pub(crate) fn is_scalar_add_possible_impl<T, Iter>(
&self,
block_metadata: Iter,
scalar: T,
) -> Result<(), CheckError>
where
T: DecomposableInto<u8>,
Iter: Iterator<Item = (Degree, MessageModulus, CarryModulus)>,
{
let bits_in_message = self.key.message_modulus.0.ilog2();
let decomposer =
BlockDecomposer::with_early_stop_at_zero(scalar, bits_in_message).iter_as::<u8>();
// Assumes message_modulus and carry_modulus matches between pairs of block
let mut preceding_block_carry = Degree::new(0);
for (block_metadata, scalar_block_value) in block_metadata.zip(decomposer) {
let (block_degree, block_msg_mod, block_carry_mod) = block_metadata;
let degree_after_add = block_degree + Degree::new(u64::from(scalar_block_value));
// Also need to take into account preceding_carry
let max_degree = MaxDegree::from_msg_carry_modulus(block_msg_mod, block_carry_mod);
max_degree.validate(degree_after_add + preceding_block_carry)?;
preceding_block_carry = Degree::new(degree_after_add.get() / block_msg_mod.0);
}
Ok(())
}
/// Computes homomorphically an addition between a scalar and a ciphertext.
///
/// If the operation can be performed, the result is returned in a new ciphertext.
/// Otherwise a [CheckError] is returned.
///
/// # Example
///
/// ```rust
/// use tfhe::integer::gen_keys_radix;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
///
/// // We have 4 * 2 = 8 bits of message
/// let size = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, size);
///
/// let msg = 4;
/// let scalar = 40;
///
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically an addition:
/// let ct_res = sks.checked_scalar_add(&ct, scalar).unwrap();
///
/// // Decrypt:
/// let dec: u64 = cks.decrypt(&ct_res);
/// assert_eq!(msg + scalar, dec);
/// ```
pub fn checked_scalar_add<T, C>(&self, ct: &C, scalar: T) -> Result<C, CheckError>
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
self.is_scalar_add_possible(ct, scalar)?;
Ok(self.unchecked_scalar_add(ct, scalar))
}
/// Computes homomorphically an addition between a scalar and a ciphertext.
///
/// If the operation can be performed, the result is stored in the `ct_left` ciphertext.
/// Otherwise a [CheckError] is returned, and `ct_left` is not modified.
pub fn checked_scalar_add_assign<T, C>(&self, ct: &mut C, scalar: T) -> Result<(), CheckError>
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
self.is_scalar_add_possible(ct, scalar)?;
self.unchecked_scalar_add_assign(ct, scalar);
Ok(())
}
/// Computes homomorphically the addition of ciphertext with a scalar.
///
/// The result is returned in a new ciphertext.
///
/// # Example
///
/// ```rust
/// use tfhe::integer::gen_keys_radix;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
///
/// // We have 4 * 2 = 8 bits of message
/// let size = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, size);
///
/// let msg = 4;
/// let scalar = 40;
///
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically an addition:
/// let ct_res = sks.smart_scalar_add(&mut ct, scalar);
///
/// // Decrypt:
/// let dec: u64 = cks.decrypt(&ct_res);
/// assert_eq!(msg + scalar, dec);
/// ```
pub fn smart_scalar_add<T, C>(&self, ct: &mut C, scalar: T) -> C
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
if self.is_scalar_add_possible(ct, scalar).is_err() {
self.full_propagate(ct);
}
self.is_scalar_add_possible(ct, scalar).unwrap();
let mut ct = ct.clone();
self.unchecked_scalar_add_assign(&mut ct, scalar);
ct
}
/// Computes homomorphically the addition of ciphertext with a scalar.
///
/// The result is assigned to the `ct_left` ciphertext.
///
/// # Example
///
/// ```rust
/// use tfhe::integer::gen_keys_radix;
/// use tfhe::shortint::parameters::PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128;
///
/// // We have 4 * 2 = 8 bits of message
/// let size = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, size);
///
/// let msg = 129;
/// let scalar = 40;
///
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically an addition:
/// sks.smart_scalar_add_assign(&mut ct, scalar);
///
/// // Decrypt:
/// let dec: u64 = cks.decrypt(&ct);
/// assert_eq!(msg + scalar, dec);
/// ```
pub fn smart_scalar_add_assign<T, C>(&self, ct: &mut C, scalar: T)
where
T: DecomposableInto<u8>,
C: IntegerRadixCiphertext,
{
if self.is_scalar_add_possible(ct, scalar).is_err() {
self.full_propagate(ct);
}
self.is_scalar_add_possible(ct, scalar).unwrap();
self.unchecked_scalar_add_assign(ct, scalar);
}
}