@@ -6,10 +6,11 @@ VmpPMatToMut, VmpPMatToRef, ZnxInfos,
     },
     oep::{
         VmpApplyDftToDftAddImpl, VmpApplyDftToDftAddTmpBytesImpl, VmpApplyDftToDftImpl, VmpApplyDftToDftTmpBytesImpl,
-        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl,
+        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl, VmpZeroImpl,
     },
     reference::fft64::vmp::{
         vmp_apply_dft_to_dft, vmp_apply_dft_to_dft_add, vmp_apply_dft_to_dft_tmp_bytes, vmp_prepare, vmp_prepare_tmp_bytes,
+        vmp_zero,
     },
 };
 
@@ -141,3 +142,12 @@ ) -> usize {
         vmp_apply_dft_to_dft_tmp_bytes(a_size, b_rows, b_cols_in)
     }
 }
+
+unsafe impl VmpZeroImpl<Self> for FFT64Avx {
+    fn vmp_zero_impl<R>(_module: &Module<Self>, res: &mut R)
+    where
+        R: VmpPMatToMut<Self>,
+    {
+        vmp_zero(res);
+    }
+}

@@ -6,10 +6,11 @@ VmpPMatToMut, VmpPMatToRef, ZnxInfos,
     },
     oep::{
         VmpApplyDftToDftAddImpl, VmpApplyDftToDftAddTmpBytesImpl, VmpApplyDftToDftImpl, VmpApplyDftToDftTmpBytesImpl,
-        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl,
+        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl, VmpZeroImpl,
     },
     reference::fft64::vmp::{
         vmp_apply_dft_to_dft, vmp_apply_dft_to_dft_add, vmp_apply_dft_to_dft_tmp_bytes, vmp_prepare, vmp_prepare_tmp_bytes,
+        vmp_zero,
     },
 };
 
@@ -141,3 +142,12 @@ ) -> usize {
         vmp_apply_dft_to_dft_tmp_bytes(a_size, b_rows, b_cols_in)
     }
 }
+
+unsafe impl VmpZeroImpl<Self> for FFT64Ref {
+    fn vmp_zero_impl<R>(_module: &Module<Self>, res: &mut R)
+    where
+        R: VmpPMatToMut<Self>,
+    {
+        vmp_zero(res);
+    }
+}

@@ -6,8 +6,9 @@ VmpPMatToMut, VmpPMatToRef, ZnxInfos, ZnxView, ZnxViewMut,
     },
     oep::{
         VmpApplyDftToDftAddImpl, VmpApplyDftToDftAddTmpBytesImpl, VmpApplyDftToDftImpl, VmpApplyDftToDftTmpBytesImpl,
-        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPMatFromBytesImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl,
+        VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPMatFromBytesImpl, VmpPrepareImpl, VmpPrepareTmpBytesImpl, VmpZeroImpl,
     },
+    reference::fft64::vmp::vmp_zero,
 };
 
 use crate::cpu_spqlios::{
@@ -269,3 +270,12 @@ )
         }
     }
 }
+
+unsafe impl VmpZeroImpl<Self> for FFT64Spqlios {
+    fn vmp_zero_impl<R>(_module: &Module<Self>, res: &mut R)
+    where
+        R: VmpPMatToMut<Self>,
+    {
+        vmp_zero(res);
+    }
+}

@@ -1,5 +1,5 @@
 use poulpy_hal::{
-    api::{VmpPMatAlloc, VmpPMatBytesOf, VmpPrepare, VmpPrepareTmpBytes},
+    api::{VmpPMatAlloc, VmpPMatBytesOf, VmpPrepare, VmpPrepareTmpBytes, VmpZero},
     layouts::{Backend, Data, DataMut, DataRef, Module, Scratch, VmpPMat, VmpPMatToMut, VmpPMatToRef, ZnxInfos},
 };
 
@@ -51,7 +51,7 @@ }
 
 pub trait GGSWPreparedFactory<B: Backend>
 where
-    Self: GetDegree + VmpPMatAlloc<B> + VmpPMatBytesOf + VmpPrepareTmpBytes + VmpPrepare<B>,
+    Self: GetDegree + VmpPMatAlloc<B> + VmpPMatBytesOf + VmpPrepareTmpBytes + VmpPrepare<B> + VmpZero<B>,
 {
     fn alloc_ggsw_prepared(
         &self,
@@ -163,7 +163,7 @@ }
 }
 
 impl<B: Backend> GGSWPreparedFactory<B> for Module<B> where
-    Self: GetDegree + VmpPMatAlloc<B> + VmpPMatBytesOf + VmpPrepareTmpBytes + VmpPrepare<B>
+    Self: GetDegree + VmpPMatAlloc<B> + VmpPMatBytesOf + VmpPrepareTmpBytes + VmpPrepare<B> + VmpZero<B>
 {
 }
 
@@ -222,6 +222,13 @@ O: GGSWToRef,
         M: GGSWPreparedFactory<B>,
     {
         module.ggsw_prepare(self, other, scratch);
+    }
+
+    pub fn zero<M>(&mut self, module: &M)
+    where
+        M: GGSWPreparedFactory<B>,
+    {
+        module.vmp_zero(&mut self.data);
     }
 }
 

@@ -155,11 +155,7 @@ scratch,
         )
     }
 
-    fn take_ggsw_slice<A>(
-        &mut self,
-        size: usize,
-        infos: &A,
-    ) -> (Vec<GGSW<&mut [u8]>>, &mut Self)
+    fn take_ggsw_slice<A>(&mut self, size: usize, infos: &A) -> (Vec<GGSW<&mut [u8]>>, &mut Self)
     where
         A: GGSWInfos,
     {

@@ -111,3 +111,9 @@ R: VecZnxDftToMut<B>,
         A: VecZnxDftToRef<B>,
         C: VmpPMatToRef<B>;
 }
+
+pub trait VmpZero<B: Backend> {
+    fn vmp_zero<R>(&self, res: &mut R)
+    where
+        R: VmpPMatToMut<B>;
+}

@@ -1,7 +1,7 @@
 use crate::{
     api::{
         VmpApplyDft, VmpApplyDftTmpBytes, VmpApplyDftToDft, VmpApplyDftToDftAdd, VmpApplyDftToDftAddTmpBytes,
-        VmpApplyDftToDftTmpBytes, VmpPMatAlloc, VmpPMatBytesOf, VmpPMatFromBytes, VmpPrepare, VmpPrepareTmpBytes,
+        VmpApplyDftToDftTmpBytes, VmpPMatAlloc, VmpPMatBytesOf, VmpPMatFromBytes, VmpPrepare, VmpPrepareTmpBytes, VmpZero,
     },
     layouts::{
         Backend, MatZnxToRef, Module, Scratch, VecZnxDftToMut, VecZnxDftToRef, VecZnxToRef, VmpPMatOwned, VmpPMatToMut,
@@ -10,7 +10,7 @@ },
     oep::{
         VmpApplyDftImpl, VmpApplyDftTmpBytesImpl, VmpApplyDftToDftAddImpl, VmpApplyDftToDftAddTmpBytesImpl, VmpApplyDftToDftImpl,
         VmpApplyDftToDftTmpBytesImpl, VmpPMatAllocBytesImpl, VmpPMatAllocImpl, VmpPMatFromBytesImpl, VmpPrepareImpl,
-        VmpPrepareTmpBytesImpl,
+        VmpPrepareTmpBytesImpl, VmpZeroImpl,
     },
 };
 
@@ -161,3 +161,15 @@ {
         B::vmp_apply_dft_to_dft_add_impl(self, res, a, b, scale, scratch);
     }
 }
+
+impl<B> VmpZero<B> for Module<B>
+where
+    B: Backend + VmpZeroImpl<B>,
+{
+    fn vmp_zero<R>(&self, res: &mut R)
+    where
+        R: VmpPMatToMut<B>,
+    {
+        B::vmp_zero_impl(self, res);
+    }
+}

@@ -145,3 +145,13 @@ R: VecZnxDftToMut<B>,
         A: VecZnxDftToRef<B>,
         C: VmpPMatToRef<B>;
 }
+
+/// # THIS TRAIT IS AN OPEN EXTENSION POINT (unsafe)
+/// * See TODO.
+/// * See [crate::api::VmpZero] for corresponding public API.
+/// # Safety [crate::doc::backend_safety] for safety contract.
+pub unsafe trait VmpZeroImpl<B: Backend> {
+    fn vmp_zero_impl<R>(module: &Module<B>, res: &mut R)
+    where
+        R: VmpPMatToMut<B>;
+}

@@ -1,6 +1,6 @@
 use crate::{
     cast_mut,
-    layouts::{MatZnx, MatZnxToRef, VecZnx, VecZnxToRef, VmpPMatToMut, ZnxView, ZnxViewMut},
+    layouts::{DataViewMut, MatZnx, MatZnxToRef, VecZnx, VecZnxToRef, VmpPMatToMut, ZnxView, ZnxViewMut},
     oep::VecZnxDftAllocBytesImpl,
     reference::fft64::{
         reim::{ReimDFTExecute, ReimFFTTable, ReimFromZnx, ReimZero},
@@ -155,6 +155,13 @@
 pub fn vmp_apply_dft_to_dft_tmp_bytes(a_size: usize, prows: usize, pcols_in: usize) -> usize {
     let row_max: usize = (a_size).min(prows);
     (16 + 8 * row_max * pcols_in) * size_of::<f64>()
+}
+
+pub fn vmp_zero<R, BE: Backend>(res: &mut R)
+where
+    R: VmpPMatToMut<BE>,
+{
+    res.to_mut().data_mut().fill(0);
 }
 
 pub fn vmp_apply_dft_to_dft<R, A, M, BE>(res: &mut R, a: &A, pmat: &M, tmp_bytes: &mut [f64])

@@ -217,6 +217,19 @@ DM: DataMut,
         DB: DataRef,
         DK: DataRef,
         K: BDDKeyHelper<DK, BRA, BE>;
+    fn fhe_uint_prepare_custom<DM, DB, DK, K>(
+        &self,
+        res: &mut FheUintPrepared<DM, T, BE>,
+        bits: &FheUint<DB, T>,
+        bit_start: usize,
+        bit_end: usize,
+        key: &K,
+        scratch: &mut Scratch<BE>,
+    ) where
+        DM: DataMut,
+        DB: DataRef,
+        DK: DataRef,
+        K: BDDKeyHelper<DK, BRA, BE>;
 }
 
 impl<BRA: BlindRotationAlgo, BE: Backend, T: UnsignedInteger> FheUintPrepare<BRA, T, BE> for Module<BE>
@@ -241,6 +254,23 @@ fn fhe_uint_prepare<DM, DB, DK, K>(
         &self,
         res: &mut FheUintPrepared<DM, T, BE>,
         bits: &FheUint<DB, T>,
+        key: &K,
+        scratch: &mut Scratch<BE>,
+    ) where
+        DM: DataMut,
+        DB: DataRef,
+        DK: DataRef,
+        K: BDDKeyHelper<DK, BRA, BE>,
+    {
+        self.fhe_uint_prepare_custom(res, bits, 0, T::BITS as usize, key, scratch);
+    }
+
+    fn fhe_uint_prepare_custom<DM, DB, DK, K>(
+        &self,
+        res: &mut FheUintPrepared<DM, T, BE>,
+        bits: &FheUint<DB, T>,
+        bit_start: usize,
+        bit_end: usize,
         key: &K,
         scratch: &mut Scratch<BE>,
     ) where
@@ -253,11 +283,20 @@ let (cbt, ks) = key.get_cbt_key();
 
         let mut lwe: LWE<Vec<u8>> = LWE::alloc_from_infos(bits); //TODO: add TakeLWE
         let (mut tmp_ggsw, scratch_1) = scratch.take_ggsw(res);
-        for (bit, dst) in res.bits.iter_mut().enumerate() {
+        for (bit, dst) in res.bits[bit_start..bit_end].iter_mut().enumerate() {
+            // TODO: set the rest of the bits to a prepared zero GGSW
             bits.get_bit_lwe(self, bit, &mut lwe, ks, scratch_1);
             cbt.execute_to_constant(self, &mut tmp_ggsw, &lwe, 1, 1, scratch_1);
             dst.prepare(self, &tmp_ggsw, scratch_1);
         }
+
+        for i in 0..bit_start {
+            res.bits[i].zero(self);
+        }
+
+        for i in bit_end..T::BITS as usize {
+            res.bits[i].zero(self);
+        }
     }
 }
 
@@ -272,5 +311,23 @@ M: FheUintPrepare<BRA, T, BE>,
         Scratch<BE>: ScratchTakeCore<BE>,
     {
         module.fhe_uint_prepare(self, other, key, scratch);
+    }
+    pub fn prepare_partial<BRA, M, O, K, DK>(
+        &mut self,
+        module: &M,
+        other: &FheUint<O, T>,
+        bit_start: usize,
+        bit_end: usize,
+        key: &K,
+        scratch: &mut Scratch<BE>,
+    ) where
+        BRA: BlindRotationAlgo,
+        O: DataRef,
+        DK: DataRef,
+        K: BDDKeyHelper<DK, BRA, BE>,
+        M: FheUintPrepare<BRA, T, BE>,
+        Scratch<BE>: ScratchTakeCore<BE>,
+    {
+        module.fhe_uint_prepare_custom(self, other, bit_start, bit_end, key, scratch);
     }
 }