1use crate::{
 2    ciphertext::{Ciphertext, GadgetCiphertext},
 3    elem::Elem,
 4    keys::SecretKey,
 5    parameters::Parameters,
 6    plaintext::Plaintext,
 7};
 8use base2k::{Module, SvpPPol, SvpPPolOps, VecZnxDft};
 9use std::cmp::min;
10
11pub struct Decryptor {
12    sk: SvpPPol,
13}
14
15impl Decryptor {
16    pub fn new(params: &Parameters, sk: &SecretKey) -> Self {
17        let mut sk_svp_ppol: SvpPPol = params.module().new_svp_ppol();
18        sk.prepare(params.module(), &mut sk_svp_ppol);
19        Self { sk: sk_svp_ppol }
20    }
21}
22
23pub fn decrypt_rlwe_thread_safe_tmp_byte(module: &Module, limbs: usize) -> usize {
24    module.bytes_of_vec_znx_dft(limbs) + module.vec_znx_big_normalize_tmp_bytes()
25}
26
27impl Parameters {
28    pub fn decrypt_rlwe_thread_safe_tmp_byte(&self, log_q: usize) -> usize {
29        decrypt_rlwe_thread_safe_tmp_byte(
30            self.module(),
31            (log_q + self.log_base2k() - 1) / self.log_base2k(),
32        )
33    }
34
35    pub fn decrypt_rlwe_thread_safe(
36        &self,
37        res: &mut Plaintext,
38        ct: &Ciphertext,
39        sk: &SvpPPol,
40        tmp_bytes: &mut [u8],
41    ) {
42        decrypt_rlwe_thread_safe(self.module(), &mut res.0, &ct.0, sk, tmp_bytes)
43    }
44}
45
46pub fn decrypt_rlwe_thread_safe(
47    module: &Module,
48    res: &mut Elem,
49    a: &Elem,
50    sk: &SvpPPol,
51    tmp_bytes: &mut [u8],
52) {
53    assert!(
54        tmp_bytes.len() >= decrypt_rlwe_thread_safe_tmp_byte(module, a.limbs()),
55        "invalid tmp_bytes: tmp_bytes.len()={} < decrypt_rlwe_thread_safe_tmp_byte={}",
56        tmp_bytes.len(),
57        decrypt_rlwe_thread_safe_tmp_byte(module, a.limbs())
58    );
59
60    let res_dft_bytes: usize = module.bytes_of_vec_znx_dft(a.limbs());
61
62    let mut res_dft: VecZnxDft = VecZnxDft::from_bytes(a.limbs(), tmp_bytes);
63    let mut res_big: base2k::VecZnxBig = res_dft.as_vec_znx_big();
64
65    // res_dft <- DFT(ct[1]) * DFT(sk)
66    module.svp_apply_dft(&mut res_dft, sk, &a.value[1], a.limbs());
67    // res_big <- ct[1] x sk
68    module.vec_znx_idft_tmp_a(&mut res_big, &mut res_dft, a.limbs());
69    // res_big <- ct[1] x sk + ct[0]
70    module.vec_znx_big_add_small_inplace(&mut res_big, &a.value[0]);
71    // res <- normalize(ct[1] x sk + ct[0])
72    module.vec_znx_big_normalize(
73        a.log_base2k(),
74        res.at_mut(0),
75        &res_big,
76        &mut tmp_bytes[res_dft_bytes..],
77    );
78
79    res.log_base2k = a.log_base2k();
80    res.log_q = min(res.log_q(), a.log_q());
81    res.log_scale = a.log_scale();
82}