Added support for arbitrary extended LUT

core/src/blind_rotation/lut.rs

@@ -0,0 +1,84 @@
+use backend::{FFT64, Module, ScratchOwned, VecZnx, VecZnxAlloc, VecZnxOps, ZnxInfos, ZnxViewMut, alloc_aligned};
+
+pub struct LookUpTable {
+    pub(crate) data: Vec<VecZnx<Vec<u8>>>,
+    pub(crate) basek: usize,
+    pub(crate) k: usize,
+}
+
+impl LookUpTable {
+    pub fn alloc(module: &Module<FFT64>, basek: usize, k: usize, extend_factor: usize) -> Self {
+        let size: usize = k.div_ceil(basek);
+        let mut data: Vec<VecZnx<Vec<u8>>> = Vec::with_capacity(extend_factor);
+        (0..extend_factor).for_each(|_| {
+            data.push(module.new_vec_znx(1, size));
+        });
+        Self { data, basek, k }
+    }
+
+    pub fn set(&mut self, module: &Module<FFT64>, f: fn(i64) -> i64, message_modulus: usize) {
+        let basek: usize = self.basek;
+
+        // Get the number minimum limb to store the message modulus
+        let limbs: usize = message_modulus.div_ceil(1 << basek);
+
+        // Scaling factor
+        let scale: i64 = (1 << (basek * limbs - 1)).div_round(message_modulus) as i64;
+
+        // Updates function
+        let f_scaled = |x: i64| (f(x) % message_modulus as i64) * scale;
+
+        // If LUT size > module.n()
+        let domain_size: usize = self.data[0].n() * self.data.len();
+
+        let size: usize = self.k.div_ceil(self.basek);
+
+        // Equivalent to AUTO([f(0), f(1), ..., f(n-1)], -1)
+        let mut lut_full: VecZnx<Vec<u8>> = VecZnx::new::<i64>(domain_size, 1, size);
+        {
+            let lut_at: &mut [i64] = lut_full.at_mut(0, limbs - 1);
+
+            let start: usize = 0;
+            let end: usize = (domain_size).div_round(message_modulus);
+
+            let y: i64 = f_scaled(0);
+            (start..end).for_each(|i| {
+                lut_at[i] = y;
+            });
+
+            (1..message_modulus).for_each(|x| {
+                let start: usize = (x * domain_size).div_round(message_modulus);
+                let end: usize = ((x + 1) * domain_size).div_round(message_modulus);
+                let y: i64 = f_scaled(x as i64);
+                (start..end).for_each(|i| {
+                    lut_at[domain_size - i] = -y;
+                })
+            });
+        }
+
+        // Rotates half the step to the left
+        let half_step: usize = domain_size.div_round(message_modulus << 1);
+        module.vec_znx_rotate_inplace(-(half_step as i64), &mut lut_full, 0);
+
+        let mut tmp_bytes: Vec<u8> = alloc_aligned(lut_full.n() * size_of::<i64>());
+        lut_full.normalize(self.basek, 0, &mut tmp_bytes);
+
+        if self.data.len() > 1 {
+            let mut scratch: ScratchOwned = ScratchOwned::new(module.bytes_of_vec_znx(1, size));
+            module.vec_znx_split(&mut self.data, 0, &lut_full, 0, scratch.borrow());
+        } else {
+            module.vec_znx_copy(&mut self.data[0], 0, &lut_full, 0);
+        }
+    }
+}
+
+pub trait DivRound {
+    fn div_round(self, rhs: Self) -> Self;
+}
+
+impl DivRound for usize {
+    #[inline]
+    fn div_round(self, rhs: Self) -> Self {
+        (self + rhs / 2) / rhs
+    }
+}