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Added noise equation for keyswitch over GGSW & updated associated test

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This commit is contained in:
Jean-Philippe Bossuat
2025-05-20 14:36:26 +02:00
parent 7d84477e64
commit a803127424
5 changed files with 107 additions and 29 deletions
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35
core/src/test_fft64/gglwe.rs
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@@ -212,7 +212,7 @@ fn test_key_switch(
module.vec_znx_sub_scalar_inplace(&mut pt, 0, row_i, &sk0, col_i);
let noise_have: f64 = pt.data.std(0, basek).log2();
let noise_want: f64 = noise_gglwe_product(
let noise_want: f64 = log2_std_noise_gglwe_product(
module.n() as f64,
basek,
0.5,
@@ -314,7 +314,7 @@ fn test_key_switch_inplace(log_n: usize, basek: usize, k_ksk: usize, sigma: f64,
module.vec_znx_sub_scalar_inplace(&mut pt, 0, row_i, &sk0, col_i);
let noise_have: f64 = pt.data.std(0, basek).log2();
let noise_want: f64 = noise_gglwe_product(
let noise_want: f64 = log2_std_noise_gglwe_product(
module.n() as f64,
basek,
0.5,
@@ -571,7 +571,7 @@ fn test_external_product_inplace(log_n: usize, basek: usize, k: usize, sigma: f6
});
}
pub(crate) fn noise_gglwe_product(
pub(crate) fn var_noise_gglwe_product(
n: f64,
basek: usize,
var_xs: f64,
@@ -597,7 +597,34 @@ pub(crate) fn noise_gglwe_product(
let mut noise: f64 = (a_cols as f64) * n * var_base * (var_gct_err_lhs + var_xs * var_gct_err_rhs);
noise += var_msg * var_a_err * a_scale * a_scale * n;
noise *= rank_in;
noise /= b_scale * b_scale;
noise
}
pub(crate) fn log2_std_noise_gglwe_product(
n: f64,
basek: usize,
var_xs: f64,
var_msg: f64,
var_a_err: f64,
var_gct_err_lhs: f64,
var_gct_err_rhs: f64,
rank_in: f64,
a_logq: usize,
b_logq: usize,
) -> f64 {
let mut noise: f64 = var_noise_gglwe_product(
n,
basek,
var_xs,
var_msg,
var_a_err,
var_gct_err_lhs,
var_gct_err_rhs,
rank_in,
a_logq,
b_logq,
);
noise = noise.sqrt();
noise /= b_scale;
noise.log2().min(-1.0) // max noise is [-2^{-1}, 2^{-1}]
}