1use backend::{FFT64, Module, VecZnx, VecZnxAlloc, VecZnxOps, ZnxInfos, ZnxViewMut, alloc_aligned};
  2
  3pub struct LookUpTable {
  4    pub(crate) data: Vec<VecZnx<Vec<u8>>>,
  5    pub(crate) basek: usize,
  6    pub(crate) k: usize,
  7}
  8
  9impl LookUpTable {
 10    pub fn alloc(module: &Module<FFT64>, basek: usize, k: usize, extension_factor: usize) -> Self {
 11        let size: usize = k.div_ceil(basek);
 12        let mut data: Vec<VecZnx<Vec<u8>>> = Vec::with_capacity(extension_factor);
 13        (0..extension_factor).for_each(|_| {
 14            data.push(module.new_vec_znx(1, size));
 15        });
 16        Self { data, basek, k }
 17    }
 18
 19    pub fn extension_factor(&self) -> usize {
 20        self.data.len()
 21    }
 22
 23    pub fn domain_size(&self) -> usize {
 24        self.data.len() * self.data[0].n()
 25    }
 26
 27    pub fn set(&mut self, module: &Module<FFT64>, f: &Vec<i64>, k: usize) {
 28        assert!(f.len() <= module.n());
 29
 30        let basek: usize = self.basek;
 31
 32        // Get the number minimum limb to store the message modulus
 33        let limbs: usize = k.div_ceil(1 << basek);
 34
 35        // Scaling factor
 36        let scale: i64 = (1 << (basek * limbs - 1)).div_round(k) as i64;
 37
 38        // #elements in lookup table
 39        let f_len: usize = f.len();
 40
 41        // If LUT size > module.n()
 42        let domain_size: usize = self.domain_size();
 43
 44        let size: usize = self.k.div_ceil(self.basek);
 45
 46        // Equivalent to AUTO([f(0), -f(n-1), -f(n-2), ..., -f(1)], -1)
 47        let mut lut_full: VecZnx<Vec<u8>> = VecZnx::new::<i64>(domain_size, 1, size);
 48
 49        let lut_at: &mut [i64] = lut_full.at_mut(0, limbs - 1);
 50
 51        f.iter().enumerate().for_each(|(i, fi)| {
 52            let start: usize = (i * domain_size).div_round(f_len);
 53            let end: usize = ((i + 1) * domain_size).div_round(f_len);
 54            lut_at[start..end].fill(fi * scale);
 55        });
 56
 57        // Rotates half the step to the left
 58        let half_step: usize = domain_size.div_round(f_len << 1);
 59
 60        lut_full.rotate(-(half_step as i64));
 61
 62        let mut tmp_bytes: Vec<u8> = alloc_aligned(lut_full.n() * size_of::<i64>());
 63        lut_full.normalize(self.basek, 0, &mut tmp_bytes);
 64
 65        if self.extension_factor() > 1 {
 66            (0..self.extension_factor()).for_each(|i| {
 67                module.switch_degree(&mut self.data[i], 0, &lut_full, 0);
 68                if i < self.extension_factor() {
 69                    lut_full.rotate(-1);
 70                }
 71            });
 72        } else {
 73            module.vec_znx_copy(&mut self.data[0], 0, &lut_full, 0);
 74        }
 75    }
 76
 77    #[allow(dead_code)]
 78    pub(crate) fn rotate(&mut self, k: i64) {
 79        let extension_factor: usize = self.extension_factor();
 80        let two_n: usize = 2 * self.data[0].n();
 81        let two_n_ext: usize = two_n * extension_factor;
 82
 83        let k_pos: usize = ((k + two_n_ext as i64) % two_n_ext as i64) as usize;
 84
 85        let k_hi: usize = k_pos / extension_factor;
 86        let k_lo: usize = k_pos % extension_factor;
 87
 88        (0..extension_factor - k_lo).for_each(|i| {
 89            self.data[i].rotate(k_hi as i64);
 90        });
 91
 92        (extension_factor - k_lo..extension_factor).for_each(|i| {
 93            self.data[i].rotate(k_hi as i64 + 1);
 94        });
 95
 96        self.data.rotate_right(k_lo as usize);
 97    }
 98}
 99
100pub(crate) trait DivRound {
101    fn div_round(self, rhs: Self) -> Self;
102}
103
104impl DivRound for usize {
105    #[inline]
106    fn div_round(self, rhs: Self) -> Self {
107        (self + rhs / 2) / rhs
108    }
109}