rs_tfhe 0.2.0

//! Lookup table implementation for programmable bootstrapping
//!
//! A lookup table is a TRLWE ciphertext that encodes a function for evaluation
//! during programmable bootstrapping operations.

use crate::params;
use crate::trlwe::TRLWELv1;

/// Lookup table for programmable bootstrapping
///
/// A lookup table is a TRLWE ciphertext that encodes a function
/// for programmable bootstrapping. During blind rotation, the LUT is rotated
/// based on the encrypted value, effectively evaluating the function on the
/// encrypted data.
#[derive(Debug, Clone)]
pub struct LookupTable {
  /// Polynomial encoding the function values
  pub poly: TRLWELv1,
}

impl LookupTable {
  /// Create a new lookup table
  pub fn new() -> Self {
    Self {
      poly: TRLWELv1::new(),
    }
  }

  /// Create a lookup table from an existing TRLWE polynomial
  ///
  /// # Arguments
  /// * `poly` - TRLWE polynomial containing the encoded function
  pub fn from_poly(poly: TRLWELv1) -> Self {
    Self { poly }
  }

  /// Get a reference to the underlying polynomial
  pub fn poly(&self) -> &TRLWELv1 {
    &self.poly
  }

  /// Get a mutable reference to the underlying polynomial
  pub fn poly_mut(&mut self) -> &mut TRLWELv1 {
    &mut self.poly
  }

  /// Copy values from another lookup table
  ///
  /// # Arguments
  /// * `other` - Source lookup table to copy from
  pub fn copy_from(&mut self, other: &LookupTable) {
    self.poly.a.copy_from_slice(&other.poly.a);
    self.poly.b.copy_from_slice(&other.poly.b);
  }

  /// Clear the lookup table (sets all coefficients to 0)
  pub fn clear(&mut self) {
    let n = params::trgsw_lv1::N;
    self.poly.a[..n].fill(0);
    self.poly.b[..n].fill(0);
  }

  /// Check if the lookup table is empty (all coefficients are zero)
  pub fn is_empty(&self) -> bool {
    let n = params::trgsw_lv1::N;
    self.poly.a[..n].iter().all(|&x| x == 0) && self.poly.b[..n].iter().all(|&x| x == 0)
  }
}

impl Default for LookupTable {
  fn default() -> Self {
    Self::new()
  }
}

impl From<TRLWELv1> for LookupTable {
  fn from(poly: TRLWELv1) -> Self {
    Self::from_poly(poly)
  }
}

impl From<LookupTable> for TRLWELv1 {
  fn from(lut: LookupTable) -> Self {
    lut.poly
  }
}

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  fn test_lookup_table_creation() {
    let lut = LookupTable::new();
    assert!(lut.is_empty());
  }

  #[test]
  fn test_lookup_table_from_poly() {
    let mut poly = TRLWELv1::new();
    poly.b[0] = 1;

    let lut = LookupTable::from_poly(poly);
    assert!(!lut.is_empty());
  }

  #[test]
  fn test_lookup_table_copy() {
    let mut lut1 = LookupTable::new();
    let mut lut2 = LookupTable::new();

    // Set some values in lut1
    lut1.poly.b[0] = 42;
    lut1.poly.b[1] = 24;

    // Copy to lut2
    lut2.copy_from(&lut1);

    assert_eq!(lut2.poly.b[0], 42);
    assert_eq!(lut2.poly.b[1], 24);
  }

  #[test]
  fn test_lookup_table_clear() {
    let mut lut = LookupTable::new();

    // Set some values
    lut.poly.b[0] = 42;
    lut.poly.b[1] = 24;
    assert!(!lut.is_empty());

    // Clear and check
    lut.clear();
    assert!(lut.is_empty());
  }

  #[test]
  fn test_lookup_table_conversions() {
    let mut poly = TRLWELv1::new();
    poly.b[0] = 123;

    // From TRLWELv1 to LookupTable
    let lut = LookupTable::from(poly);
    assert_eq!(lut.poly.b[0], 123);

    // From LookupTable to TRLWELv1
    let poly_back: TRLWELv1 = lut.into();
    assert_eq!(poly_back.b[0], 123);
  }
}