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fix decoding to use rounded division instead of arithmetic right shift

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This commit is contained in:
Pro7ech
2025-11-06 11:18:41 +01:00
parent dc2d399602
commit 785bb46df2
2 changed files with 46 additions and 6 deletions
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24
poulpy-hal/src/layouts/encoding.rs
View File

@@ -164,13 +164,15 @@ impl<D: DataRef> VecZnx<D> {
data.copy_from_slice(a.at(col, 0));
let rem: usize = base2k - (k % base2k);
if k < base2k {
data.iter_mut().for_each(|x| *x >>= rem);
let scale = 1 << rem as i64;
data.iter_mut().for_each(|x| *x = div_round(*x, scale));
} else {
(1..size).for_each(|i| {
if i == size - 1 && rem != base2k {
let k_rem: usize = (base2k - rem) % base2k;
let scale: i64 = 1 << rem as i64;
izip!(a.at(col, i).iter(), data.iter_mut()).for_each(|(x, y)| {
*y = (*y << k_rem) + (x >> rem);
*y = (*y << k_rem) + div_round(*x, scale);
});
} else {
izip!(a.at(col, i).iter(), data.iter_mut()).for_each(|(x, y)| {
@@ -197,7 +199,8 @@ impl<D: DataRef> VecZnx<D> {
let x: i64 = a.at(col, j)[idx];
if j == size - 1 && rem != base2k {
let k_rem: usize = (base2k - rem) % base2k;
res = (res << k_rem) + (x >> rem);
let scale: i64 = 1 << rem as i64;
res = (res << k_rem) + div_round(x, scale);
} else {
res = (res << base2k) + x;
}
@@ -293,7 +296,8 @@ impl<D: DataRef> Zn<D> {
let x: i64 = a.at(0, j)[0];
if j == size - 1 && rem != base2k {
let k_rem: usize = (base2k - rem) % base2k;
res = (res << k_rem) + (x >> rem);
let scale: i64 = 1 << rem as i64;
res = (res << k_rem) + div_round(x, scale);
} else {
res = (res << base2k) + x;
}
@@ -324,3 +328,15 @@ impl<D: DataRef> Zn<D> {
res
}
}
#[inline]
pub fn div_round(a: i64, b: i64) -> i64 {
assert!(b != 0, "division by zero");
let div: i64 = a / b;
let rem: i64 = a % b;
if (2 * rem.abs()) >= b.abs() {
div + a.signum() * b.signum()
} else {
div
}
}

28
poulpy-schemes/src/tfhe/bdd_arithmetic/ciphertexts/fhe_uint.rs
View File

@@ -1,5 +1,6 @@
use poulpy_core::{
GLWEAdd, GLWECopy, GLWEDecrypt, GLWEEncryptSk, GLWEPacking, GLWERotate, GLWESub, GLWETrace, LWEFromGLWE, ScratchTakeCore,
GLWEAdd, GLWECopy, GLWEDecrypt, GLWEEncryptSk, GLWENoise, GLWEPacking, GLWERotate, GLWESub, GLWETrace, LWEFromGLWE,
ScratchTakeCore,
layouts::{
Base2K, Degree, GGLWEInfos, GGLWEPreparedToRef, GLWE, GLWEAutomorphismKeyHelper, GLWEInfos, GLWEPlaintextLayout,
GLWESecretPreparedToRef, GLWEToMut, GLWEToRef, GetGaloisElement, LWEInfos, LWEToMut, Rank, TorusPrecision,
@@ -101,7 +102,7 @@ impl<D: DataMut, T: UnsignedInteger + ToBits> FheUint<D, T> {
let pt_infos = GLWEPlaintextLayout {
n: self.n(),
base2k: self.base2k(),
k: 1_usize.into(),
k: 2_usize.into(),
};
let (mut pt, scratch_1) = scratch.take_glwe_plaintext(&pt_infos);
@@ -113,6 +114,29 @@ impl<D: DataMut, T: UnsignedInteger + ToBits> FheUint<D, T> {
}
impl<D: DataRef, T: UnsignedInteger + FromBits> FheUint<D, T> {
pub fn noise<S, M, BE: Backend>(&self, module: &M, want: u32, sk: &S, scratch: &mut Scratch<BE>) -> f64
where
S: GLWESecretPreparedToRef<BE> + GLWEInfos,
M: ModuleLogN + GLWEDecrypt<BE> + GLWENoise<BE>,
Scratch<BE>: ScratchTakeCore<BE>,
{
#[cfg(debug_assertions)]
{
assert!(module.n().is_multiple_of(T::BITS as usize));
assert_eq!(self.n(), module.n() as u32);
assert_eq!(sk.n(), module.n() as u32);
}
let (mut pt, scratch_1) = scratch.take_glwe_plaintext(self);
let mut data_bits = vec![0i64; module.n()];
let log_gap: usize = module.log_n() - T::LOG_BITS as usize;
for i in 0..T::BITS as usize {
data_bits[T::bit_index(i) << log_gap] = want.bit(i) as i64
}
pt.encode_vec_i64(&data_bits, TorusPrecision(2));
self.bits.noise(module, sk, &pt, scratch_1)
}
pub fn decrypt<S, M, BE: Backend>(&self, module: &M, sk: &S, scratch: &mut Scratch<BE>) -> T
where
S: GLWESecretPreparedToRef<BE> + GLWEInfos,