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use crate::core_crypto::commons::utils::izip_eq;
use crate::core_crypto::prelude::CastFrom;
use crate::integer::ciphertext::RadixCiphertext;
use crate::integer::ServerKey;
use std::ops::Rem;
impl ServerKey {
/// Shifts the blocks to the right.
///
/// 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 num_blocks = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, num_blocks);
///
/// let msg = 16;
/// let shift = 2;
///
/// // Encrypt two messages:
/// let ct = cks.encrypt(msg);
///
/// let ct_res = sks.blockshift_right(&ct, shift);
///
/// let div = cks.parameters().message_modulus().0.pow(shift as u32);
///
/// // Decrypt:
/// let clear = cks.decrypt(&ct_res);
/// assert_eq!(msg / div, clear);
/// ```
pub fn blockshift_right(&self, ctxt: &RadixCiphertext, shift: usize) -> RadixCiphertext {
let mut result: RadixCiphertext = self.create_trivial_zero_radix(ctxt.blocks.len());
let limit = result.blocks.len() - shift;
for (res_i, c_i) in result.blocks[..limit]
.iter_mut()
.zip(ctxt.blocks[shift..].iter())
{
res_i.clone_from(c_i);
}
result
}
pub fn blockshift_right_assign(&self, ctxt: &mut RadixCiphertext, shift: usize) {
*ctxt = self.blockshift_right(ctxt, shift);
}
/// Computes homomorphically a right shift.
///
/// 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 num_blocks = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, num_blocks);
///
/// let msg = 128u64;
/// let shift = 2;
///
/// let ct = cks.encrypt(msg);
///
/// // Compute homomorphically a right shift:
/// let ct_res = sks.unchecked_scalar_right_shift(&ct, shift);
///
/// // Decrypt:
/// let dec = cks.decrypt(&ct_res);
/// assert_eq!(msg >> shift, dec);
/// ```
pub fn unchecked_scalar_right_shift<T>(&self, ct: &RadixCiphertext, shift: T) -> RadixCiphertext
where
T: Rem<T, Output = T> + CastFrom<u64>,
u64: CastFrom<T>,
{
let mut result = ct.clone();
self.unchecked_scalar_right_shift_assign(&mut result, shift);
result
}
/// Computes homomorphically a right shift.
///
/// 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 num_blocks = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, num_blocks);
///
/// let msg = 18u64;
/// let shift = 4;
///
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a right shift:
/// sks.unchecked_scalar_right_shift_assign(&mut ct, shift);
///
/// // Decrypt:
/// let dec = cks.decrypt(&ct);
/// assert_eq!(msg >> shift, dec);
/// ```
pub fn unchecked_scalar_right_shift_assign<T>(&self, ct: &mut RadixCiphertext, shift: T)
where
T: Rem<T, Output = T> + CastFrom<u64>,
u64: CastFrom<T>,
{
// see parallel implementation for a bit more details
debug_assert!(ct.block_carries_are_empty());
debug_assert!(self.key.carry_modulus.0 >= self.key.message_modulus.0 / 2);
let num_bits_in_block = self.key.message_modulus.0.ilog2() as u64;
let total_num_bits = num_bits_in_block * ct.blocks.len() as u64;
let shift = shift % T::cast_from(total_num_bits);
let shift = u64::cast_from(shift);
if shift == 0 {
return;
}
let rotations = ((shift / num_bits_in_block) as usize).min(ct.blocks.len());
let shift_within_block = shift % num_bits_in_block;
let num_blocks = ct.blocks.len();
// rotate left as the blocks are from LSB to MSB
ct.blocks.rotate_left(rotations);
for block in &mut ct.blocks[num_blocks - rotations..] {
self.key.create_trivial_assign(block, 0);
}
if shift_within_block == 0 || rotations == ct.blocks.len() {
return;
}
let message_modulus = self.key.message_modulus.0;
let lut = self
.key
.generate_lookup_table_bivariate(|current_block, mut previous_block| {
// left shift not to lose
// bits when shifting right afterwards
previous_block <<= num_bits_in_block;
previous_block >>= shift_within_block;
// The way of getting carry / message is reversed compared
// to the usual way but its normal
let message_of_current_block = current_block >> shift_within_block;
let carry_of_previous_block = previous_block % message_modulus;
message_of_current_block + carry_of_previous_block
});
let partial_blocks = ct.blocks[..num_blocks - rotations]
.windows(2)
.map(|blocks| {
// We are right-shifting, which in our representation
// means the previous_block (the one with the carry to be
// progatated to the current_block) is the next block in the Vec
let (current_block, previous_block) = (&blocks[0], &blocks[1]);
self.key
.unchecked_apply_lookup_table_bivariate(current_block, previous_block, &lut)
})
.collect::<Vec<_>>();
// We do this block separately as this one does not
// need to get incoming bits from it neighbour
self.key.scalar_right_shift_assign(
&mut ct.blocks[num_blocks - rotations - 1],
shift_within_block as u8,
);
// We started with num_blocks, discarded 'rotations' blocks
// and did the last one separately
let blocks_to_replace = &mut ct.blocks[..num_blocks - rotations - 1];
assert_eq!(partial_blocks.len(), blocks_to_replace.len());
for (block, shifted_block) in izip_eq!(blocks_to_replace, partial_blocks) {
*block = shifted_block;
}
debug_assert!(ct.block_carries_are_empty());
}
/// Computes homomorphically a left shift by a scalar.
///
/// 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 num_blocks = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, num_blocks);
///
/// let msg = 21u64;
/// let shift = 2;
///
/// let ct1 = cks.encrypt(msg);
///
/// // Compute homomorphically a left shift:
/// let ct_res = sks.unchecked_scalar_left_shift(&ct1, shift);
///
/// // Decrypt:
/// let dec = cks.decrypt(&ct_res);
/// assert_eq!(msg << shift, dec);
/// ```
pub fn unchecked_scalar_left_shift<T>(
&self,
ct_left: &RadixCiphertext,
shift: T,
) -> RadixCiphertext
where
T: Rem<T, Output = T> + CastFrom<u64>,
u64: CastFrom<T>,
{
let mut result = ct_left.clone();
self.unchecked_scalar_left_shift_assign(&mut result, shift);
result
}
/// Computes homomorphically a left shift by a scalar.
///
/// The result is assigned in the input ciphertext
///
/// # Requirements
///
/// - The blocks parameter's carry space have at least one more bit than message space
/// - The input ciphertext carry buffer is empty / clean
///
/// # Output
///
/// - The ct carry buffers will be clean / empty afterwards
///
/// # 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 num_blocks = 4;
/// let (cks, sks) = gen_keys_radix(PARAM_MESSAGE_2_CARRY_2_KS_PBS_GAUSSIAN_2M128, num_blocks);
///
/// let msg = 13u64;
/// let shift = 2;
///
/// let mut ct = cks.encrypt(msg);
///
/// // Compute homomorphically a right shift:
/// sks.unchecked_scalar_left_shift_assign(&mut ct, shift);
///
/// // Decrypt:
/// let dec = cks.decrypt(&ct);
/// assert_eq!(msg << shift, dec);
/// ```
pub fn unchecked_scalar_left_shift_assign<T>(&self, ct: &mut RadixCiphertext, shift: T)
where
T: Rem<T, Output = T> + CastFrom<u64>,
u64: CastFrom<T>,
{
// see parallel implementation for a bit more details
debug_assert!(ct.block_carries_are_empty());
debug_assert!(self.key.carry_modulus.0 >= self.key.message_modulus.0 / 2);
let shift = u64::cast_from(shift);
if shift == 0 {
return;
}
let num_bits_in_block = self.key.message_modulus.0.ilog2() as u64;
let total_num_bits = num_bits_in_block * ct.blocks.len() as u64;
let shift = shift % total_num_bits;
let rotations = ((shift / num_bits_in_block) as usize).min(ct.blocks.len());
let shift_within_block = shift % num_bits_in_block;
// rotate right as the blocks are from LSB to MSB
ct.blocks.rotate_right(rotations);
for block in &mut ct.blocks[..rotations] {
self.key.create_trivial_assign(block, 0);
}
if shift_within_block == 0 || rotations == ct.blocks.len() {
return;
}
let lut = self
.key
.generate_lookup_table_bivariate(|current_block, previous_block| {
let current_block = current_block << shift_within_block;
let previous_block = previous_block << shift_within_block;
let message_of_current_block = current_block % self.key.message_modulus.0;
let carry_of_previous_block = previous_block / self.key.message_modulus.0;
message_of_current_block + carry_of_previous_block
});
let partial_blocks = ct.blocks[rotations..]
.windows(2)
.map(|blocks| {
// We are right-shifting,
// so we get the bits from the next block in the vec
let (previous_block, current_block) = (&blocks[0], &blocks[1]);
self.key
.unchecked_apply_lookup_table_bivariate(current_block, previous_block, &lut)
})
.collect::<Vec<_>>();
// We do this block separately as this one does not
// need to get incoming bits from it neighbour
let block = &mut ct.blocks[rotations];
self.key
.scalar_left_shift_assign(block, shift_within_block as u8);
// We started with num_blocks, discarded 'rotations' blocks
// and did the last one separately
let blocks_to_replace = &mut ct.blocks[rotations + 1..];
assert_eq!(partial_blocks.len(), blocks_to_replace.len());
for (block, shifted_block) in izip_eq!(blocks_to_replace, partial_blocks) {
*block = shifted_block;
}
debug_assert!(ct.block_carries_are_empty());
}
}