concrete_shortint/server_key/

shift.rs

use super::ServerKey;
use crate::engine::ShortintEngine;
use crate::server_key::CheckError;
use crate::server_key::CheckError::CarryFull;
use crate::Ciphertext;

impl ServerKey {
    /// Computes homomorphically a right shift of the bits without checks.
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    ///
    /// // Generate the client key and the server key:
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    /// let ct = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// // Compute homomorphically a right shift
    /// let shift: u8 = 1;
    /// let ct_res = sks.unchecked_scalar_right_shift(&ct, shift);
    /// // |      ct_res     |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   0 1   |
    ///
    /// // Decrypt:
    /// let dec = cks.decrypt(&ct_res);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    /// assert_eq!(msg >> shift, dec);
    /// ```
    pub fn unchecked_scalar_right_shift(&self, ct: &Ciphertext, shift: u8) -> Ciphertext {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine
                .unchecked_scalar_right_shift(self, ct, shift)
                .unwrap()
        })
    }

    /// Computes homomorphically a right shift of the bits without checks.
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    /// let mut ct = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// // Compute homomorphically a right shift
    /// let shift: u8 = 1;
    /// sks.unchecked_scalar_right_shift_assign(&mut ct, shift);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   0 1   |
    ///
    /// // Decrypt:
    /// let dec = cks.decrypt(&ct);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    /// assert_eq!(msg >> shift, dec);
    /// ```
    pub fn unchecked_scalar_right_shift_assign(&self, ct: &mut Ciphertext, shift: u8) {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine
                .unchecked_scalar_right_shift_assign(self, ct, shift)
                .unwrap()
        })
    }

    /// Computes homomorphically a left shift of the bits without checks.
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    ///
    /// // Generate the client key and the server key:
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    ///
    /// let ct = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// // Compute homomorphically a left shift
    /// let shift: u8 = 1;
    /// let ct_res = sks.unchecked_scalar_left_shift(&ct, shift);
    /// // |      ct_res     |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 1  |   0 0   |
    ///
    /// // Decrypt:
    /// let msg_and_carry = cks.decrypt_message_and_carry(&ct_res);
    /// let msg_only = cks.decrypt(&ct_res);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    ///
    /// assert_eq!(msg << shift, msg_and_carry);
    /// assert_eq!((msg << shift) % modulus, msg_only);
    /// ```
    pub fn unchecked_scalar_left_shift(&self, ct: &Ciphertext, shift: u8) -> Ciphertext {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine.unchecked_scalar_left_shift(ct, shift).unwrap()
        })
    }

    /// Computes homomorphically a left shift of the bits without checks
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    /// let mut ct = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// // Compute homomorphically a left shift
    /// let shift: u8 = 1;
    /// sks.unchecked_scalar_left_shift_assign(&mut ct, shift);
    /// // |      ct     |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 1  |   0 0   |
    ///
    /// // Decrypt:
    /// let msg_and_carry = cks.decrypt_message_and_carry(&ct);
    /// let msg_only = cks.decrypt(&ct);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    ///
    /// assert_eq!(msg << shift, msg_and_carry);
    /// assert_eq!((msg << shift) % modulus, msg_only);
    /// ```
    pub fn unchecked_scalar_left_shift_assign(&self, ct: &mut Ciphertext, shift: u8) {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine
                .unchecked_scalar_left_shift_assign(ct, shift)
                .unwrap()
        })
    }

    /// Checks if the left shift operation can be applied.
    ///
    /// # Example
    ///
    ///```rust
    /// use concrete_shortint::{gen_keys, Parameters};
    ///
    /// // Generate the client key and the server key:
    /// let (cks, sks) = gen_keys(Parameters::default());
    ///
    /// let msg = 2;
    /// let shift = 5;
    /// let ct1 = cks.encrypt(msg);
    ///
    /// // Check if we can perform an addition
    /// let res = sks.is_scalar_left_shift_possible(&ct1, shift);
    ///
    /// assert_eq!(false, res);
    /// ```
    pub fn is_scalar_left_shift_possible(&self, ct1: &Ciphertext, shift: u8) -> bool {
        let final_operation_count = ct1.degree.0 << shift as usize;
        final_operation_count <= self.max_degree.0
    }

    /// Computes homomorphically a left shift of the bits.
    ///
    /// If the operation can be performed, a new ciphertext with the result is returned.
    /// Otherwise [CheckError::CarryFull] is returned.
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    ///
    /// // Generate the client key and the server key:
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    ///
    /// let ct1 = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// // Shifting 3 times is not ok, as it exceeds the carry buffer
    /// let ct_res = sks.checked_scalar_left_shift(&ct1, 3);
    /// assert!(ct_res.is_err());
    ///
    /// // Shifting 2 times is ok
    /// let shift = 2;
    /// let ct_res = sks.checked_scalar_left_shift(&ct1, shift);
    /// assert!(ct_res.is_ok());
    /// let ct_res = ct_res.unwrap();
    /// // |      ct_res     |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  1 0  |   0 0   |
    ///
    /// // Decrypt:
    /// let msg_and_carry = cks.decrypt_message_and_carry(&ct_res);
    /// let msg_only = cks.decrypt(&ct_res);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    ///
    /// assert_eq!(msg << shift, msg_and_carry);
    /// assert_eq!((msg << shift) % modulus, msg_only);
    /// ```
    pub fn checked_scalar_left_shift(
        &self,
        ct: &Ciphertext,
        shift: u8,
    ) -> Result<Ciphertext, CheckError> {
        if self.is_scalar_left_shift_possible(ct, shift) {
            let ct_result = self.unchecked_scalar_left_shift(ct, shift);
            Ok(ct_result)
        } else {
            Err(CarryFull)
        }
    }

    pub fn checked_scalar_left_shift_assign(
        &self,
        ct: &mut Ciphertext,
        shift: u8,
    ) -> Result<(), CheckError> {
        if self.is_scalar_left_shift_possible(ct, shift) {
            self.unchecked_scalar_left_shift_assign(ct, shift);
            Ok(())
        } else {
            Err(CarryFull)
        }
    }

    /// Computes homomorphically a left shift of the bits
    ///
    /// This checks that the operation is possible. In the case where the carry buffers are
    /// full, then it is automatically cleared to allow the operation.
    ///
    /// # Example
    ///
    /// ```rust
    /// use concrete_shortint::gen_keys;
    /// use concrete_shortint::parameters::PARAM_MESSAGE_2_CARRY_2;
    /// let (cks, sks) = gen_keys(PARAM_MESSAGE_2_CARRY_2);
    ///
    /// let msg = 2;
    /// let mut ct = cks.encrypt(msg);
    /// // |       ct        |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 0  |   1 0   |
    ///
    /// let shift: u8 = 1;
    /// let ct_res = sks.smart_scalar_left_shift(&mut ct, shift);
    /// // |      ct_res     |
    /// // | carry | message |
    /// // |-------|---------|
    /// // |  0 1  |   0 0   |
    ///
    /// // Decrypt:
    /// let msg_and_carry = cks.decrypt_message_and_carry(&ct_res);
    /// let msg_only = cks.decrypt(&ct_res);
    /// let modulus = cks.parameters.message_modulus.0 as u64;
    ///
    /// assert_eq!(msg << shift, msg_and_carry);
    /// assert_eq!((msg << shift) % modulus, msg_only);
    /// ```
    pub fn smart_scalar_left_shift(&self, ct: &mut Ciphertext, shift: u8) -> Ciphertext {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine.smart_scalar_left_shift(self, ct, shift).unwrap()
        })
    }

    pub fn smart_scalar_left_shift_assign(&self, ct: &mut Ciphertext, shift: u8) {
        ShortintEngine::with_thread_local_mut(|engine| {
            engine
                .smart_scalar_left_shift_assign(self, ct, shift)
                .unwrap()
        })
    }
}