Small optimization + more fixes

backend/src/lib.rs

@@ -150,7 +150,7 @@ impl Scratch {
         unsafe { &mut *(data as *mut [u8] as *mut Self) }
     }
 
-    pub fn zero(&mut self){
+    pub fn zero(&mut self) {
         self.data.fill(0);
     }
 

backend/src/mat_znx_dft_ops.rs

@@ -660,7 +660,7 @@ mod tests {
 
                     (0..*digits).for_each(|di| {
                         (0..a_cols).for_each(|col_i| {
-                            module.vec_znx_dft(digits - 1 - di, *digits, &mut a_dft, col_i, &a, col_i);
+                            module.vec_znx_dft(*digits, digits - 1 - di, &mut a_dft, col_i, &a, col_i);
                         });
 
                         if di == 0 {

backend/src/vec_znx_dft.rs

@@ -2,9 +2,7 @@ use std::marker::PhantomData;
 
 use crate::ffi::vec_znx_dft;
 use crate::znx_base::ZnxInfos;
-use crate::{
+use crate::{Backend, DataView, DataViewMut, FFT64, Module, VecZnxBig, ZnxSliceSize, ZnxView, alloc_aligned};
-    Backend, DataView, DataViewMut, FFT64, Module, VecZnxBig, ZnxSliceSize, ZnxView, alloc_aligned,
-};
 use std::fmt;
 
 pub struct VecZnxDft<D, B: Backend> {
@@ -62,11 +60,15 @@ impl<D: AsRef<[u8]>> ZnxView for VecZnxDft<D, FFT64> {
     type Scalar = f64;
 }
 
-impl<D: AsMut<[u8]> + AsRef<[u8]>> VecZnxDft<D, FFT64>{
+impl<D: AsMut<[u8]> + AsRef<[u8]>> VecZnxDft<D, FFT64> {
-    pub fn set_size(&mut self, size: usize){
+    pub fn set_size(&mut self, size: usize) {
         assert!(size <= self.data.as_ref().len() / (self.n * self.cols()));
         self.size = size
     }
+
+    pub fn max_size(&mut self) -> usize {
+        self.data.as_ref().len() / (self.n * self.cols)
+    }
 }
 
 pub(crate) fn bytes_of_vec_znx_dft<B: Backend>(module: &Module<B>, cols: usize, size: usize) -> usize {

backend/src/vec_znx_dft_ops.rs

@@ -163,10 +163,10 @@ impl VecZnxDftOps<FFT64> for Module<FFT64> {
 
         (0..min_steps).for_each(|j| {
             let limb: usize = offset + j * step;
-            if limb < a_ref.size(){
+            if limb < a_ref.size() {
                 res_mut
-                .at_mut(res_col, j)
+                    .at_mut(res_col, j)
-                .copy_from_slice(a_ref.at(a_col, limb));
+                    .copy_from_slice(a_ref.at(a_col, limb));
             }
         });
         (min_steps..res_mut.size()).for_each(|j| {

core/src/ggsw_ciphertext.rs

@@ -348,7 +348,6 @@ impl<DataSelf: AsMut<[u8]> + AsRef<[u8]>> GGSWCiphertext<DataSelf, FFT64> {
 
         let (mut tmp_dft_i, scratch1) = scratch.tmp_vec_znx_dft(module, cols, tsk.size());
         let (mut tmp_a, scratch2) = scratch1.tmp_vec_znx_dft(module, 1, (ci_dft.size() + digits - 1) / digits);
-        let res_size: usize = res.to_mut().size();
 
         {
             // Performs a key-switch for each combination of s[i]*s[j], i.e. for a0, a1, a2
@@ -363,12 +362,10 @@ impl<DataSelf: AsMut<[u8]> + AsRef<[u8]>> GGSWCiphertext<DataSelf, FFT64> {
             // =
             // (-(x0s0 + x1s1 + x2s2) + s0(a0s0 + a1s1 + a2s2), x0, x1, x2)
             (1..cols).for_each(|col_i| {
-            
                 let pmat: &MatZnxDft<DataTsk, FFT64> = &tsk.at(col_i - 1, col_j - 1).0.data; // Selects Enc(s[i]s[j])
 
                 // Extracts a[i] and multipies with Enc(s[i]s[j])
                 (0..digits).for_each(|di| {
-
                     tmp_a.set_size((ci_dft.size() + di) / digits);
 
                     // Small optimization for digits > 2
@@ -378,7 +375,7 @@ impl<DataSelf: AsMut<[u8]> + AsRef<[u8]>> GGSWCiphertext<DataSelf, FFT64> {
                     // It is possible to further ignore the last digits-1 limbs, but this introduce
                     // ~0.5 to 1 bit of additional noise, and thus not chosen here to ensure that the same
                     // noise is kept with respect to the ideal functionality.
-                    //tmp_dft_i.set_size(res_size - ((digits - di) as isize - 2).max(0) as usize);
+                    tmp_dft_i.set_size(tsk.size() - ((digits - di) as isize - 2).max(0) as usize);
 
                     module.vec_znx_dft_copy(digits, digits - 1 - di, &mut tmp_a, 0, ci_dft, col_i);
                     if di == 0 && col_i == 1 {

core/src/glwe_ciphertext.rs

@@ -1,5 +1,7 @@
 use backend::{
-    AddNormal, Backend, FillUniform, MatZnxDftOps, MatZnxDftScratch, Module, ScalarZnxAlloc, ScalarZnxDftAlloc, ScalarZnxDftOps, Scratch, VecZnx, VecZnxAlloc, VecZnxBig, VecZnxBigAlloc, VecZnxBigOps, VecZnxBigScratch, VecZnxDftAlloc, VecZnxDftOps, VecZnxOps, VecZnxToMut, VecZnxToRef, ZnxZero, FFT64
+    AddNormal, Backend, FFT64, FillUniform, MatZnxDftOps, MatZnxDftScratch, Module, ScalarZnxAlloc, ScalarZnxDftAlloc,
+    ScalarZnxDftOps, Scratch, VecZnx, VecZnxAlloc, VecZnxBig, VecZnxBigAlloc, VecZnxBigOps, VecZnxBigScratch, VecZnxDftAlloc,
+    VecZnxDftOps, VecZnxOps, VecZnxToMut, VecZnxToRef, ZnxZero,
 };
 use sampling::source::Source;
 
@@ -500,7 +502,6 @@ impl<DataSelf: AsRef<[u8]> + AsMut<[u8]>> GLWECiphertext<DataSelf> {
         ai_dft.zero();
         {
             (0..digits).for_each(|di| {
-
                 ai_dft.set_size((lhs.size() + di) / digits);
 
                 // Small optimization for digits > 2
@@ -510,7 +511,7 @@ impl<DataSelf: AsRef<[u8]> + AsMut<[u8]>> GLWECiphertext<DataSelf> {
                 // It is possible to further ignore the last digits-1 limbs, but this introduce
                 // ~0.5 to 1 bit of additional noise, and thus not chosen here to ensure that the same
                 // noise is kept with respect to the ideal functionality.
-                //res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);
+                res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);
 
                 (0..cols_in).for_each(|col_i| {
                     module.vec_znx_dft(
@@ -598,7 +599,7 @@ impl<DataSelf: AsRef<[u8]> + AsMut<[u8]>> GLWECiphertext<DataSelf> {
         let digits: usize = rhs.digits();
 
         let (mut res_dft, scratch1) = scratch.tmp_vec_znx_dft(module, cols, rhs.size()); // Todo optimise
-        let (mut a_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, (lhs.size() + digits-1) / digits);
+        let (mut a_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, (lhs.size() + digits - 1) / digits);
 
         {
             (0..digits).for_each(|di| {
@@ -612,7 +613,7 @@ impl<DataSelf: AsRef<[u8]> + AsMut<[u8]>> GLWECiphertext<DataSelf> {
                 // It is possible to further ignore the last digits-1 limbs, but this introduce
                 // ~0.5 to 1 bit of additional noise, and thus not chosen here to ensure that the same
                 // noise is kept with respect to the ideal functionality.
-                //res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);
+                res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);
 
                 (0..cols).for_each(|col_i| {
                     module.vec_znx_dft(digits, digits - 1 - di, &mut a_dft, col_i, &lhs.data, col_i);

core/src/glwe_ciphertext_fourier.rs

@@ -199,16 +199,22 @@ impl<DataSelf: AsMut<[u8]> + AsRef<[u8]>> GLWECiphertextFourier<DataSelf, FFT64>
         let cols: usize = rhs.rank() + 1;
         let digits = rhs.digits();
 
-
         // Space for VMP result in DFT domain and high precision
         let (mut res_dft, scratch1) = scratch.tmp_vec_znx_dft(module, cols, rhs.size());
         let (mut a_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, (lhs.size() + digits - 1) / digits);
 
         {
             (0..digits).for_each(|di| {
-
                 a_dft.set_size((lhs.size() + di) / digits);
-                res_dft.set_size(rhs.size() - (digits - di - 1));
+
+                // Small optimization for digits > 2
+                // VMP produce some error e, and since we aggregate vmp * 2^{di * B}, then
+                // we also aggregate ei * 2^{di * B}, with the largest error being ei * 2^{(digits-1) * B}.
+                // As such we can ignore the last digits-2 limbs safely of the sum of vmp products.
+                // It is possible to further ignore the last digits-1 limbs, but this introduce
+                // ~0.5 to 1 bit of additional noise, and thus not chosen here to ensure that the same
+                // noise is kept with respect to the ideal functionality.
+                res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);
 
                 (0..cols).for_each(|col_i| {
                     module.vec_znx_dft_copy(digits, digits - 1 - di, &mut a_dft, col_i, &lhs.data, col_i);