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Small optimization + more fixes

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This commit is contained in:
Jean-Philippe Bossuat
2025-06-11 14:31:32 +02:00
parent a673b84047
commit 655b22ef21
7 changed files with 33 additions and 27 deletions
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14
core/src/glwe_ciphertext_fourier.rs
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@@ -199,17 +199,23 @@ 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);
});