1use crate::{
 2    ciphertext::{Ciphertext, GadgetCiphertext},
 3    elem::Elem,
 4};
 5use base2k::{Infos, Module, VecZnx, VecZnxBig, VecZnxDft, VmpPMatOps};
 6
 7pub fn gadget_product_tmp_bytes(
 8    module: &Module,
 9    log_base2k: usize,
10    out_log_q: usize,
11    in_log_q: usize,
12    gct_rows: usize,
13    gct_log_q: usize,
14) -> usize {
15    let gct_cols: usize = (gct_log_q + log_base2k - 1) / log_base2k;
16    let in_limbs: usize = (in_log_q + log_base2k - 1) / log_base2k;
17    let out_limbs: usize = (out_log_q + log_base2k - 1) / log_base2k;
18    module.vmp_apply_dft_to_dft_tmp_bytes(out_limbs, in_limbs, gct_rows, gct_cols)
19        + 2 * module.bytes_of_vec_znx_dft(gct_cols)
20}
21
22/// Evaluates the gadget product res <- a x b.
23///
24/// # Arguments
25///
26/// * `module`: backend support for operations mod (X^N + 1)
27/// * `res`: an [Elem] to store (-cs + m * a + e, c) with res_ncols limbs.
28/// * `a`: a [VecZnx] of a_ncols limbs.
29/// * `b`: a [GadgetCiphertext] as a vector of (-Bs + m * 2^{-k} + E, B)
30///       containing b_nrows [VecZnx], each of b_ncols limbs.
31///
32/// # Computation
33///
34/// res = sum[min(a_ncols, b_nrows)] decomp(a, i) * (-B[i]s + m * 2^{-k*i} + E[i], B[i])
35///     = (cs + m * a + e, c) with min(res_limbs, b_cols) limbs.
36pub fn gadget_product_thread_safe(
37    module: &Module,
38    res: &mut Elem,
39    a: &VecZnx,
40    b: &GadgetCiphertext,
41    tmp_bytes: &mut [u8],
42) {
43    let log_base2k: usize = b.log_base2k();
44    let cols: usize = b.cols();
45
46    let (tmp_bytes_vmp_apply_dft, tmp_bytes) =
47        tmp_bytes.split_at_mut(module.bytes_of_vec_znx_dft(cols));
48
49    let (tmp_bytes_c1_dft, tmp_bytes_res_dft) = tmp_bytes.split_at_mut(tmp_bytes.len() >> 1);
50
51    let mut c1_dft: VecZnxDft = module.new_vec_znx_from_bytes(cols, tmp_bytes_c1_dft);
52    let mut res_dft: VecZnxDft = module.new_vec_znx_from_bytes(cols, tmp_bytes_res_dft);
53    let mut res_big: VecZnxBig = res_dft.as_vec_znx_big();
54
55    // c1_dft <- DFT(c1) [cols]
56    module.vec_znx_dft(&mut c1_dft, a, a.limbs());
57
58    // res_dft <- sum[rows] DFT(c1)[cols] x GadgetCiphertext[0][cols]
59    module.vmp_apply_dft_to_dft(&mut res_dft, &c1_dft, &b.value[0], tmp_bytes_vmp_apply_dft);
60
61    // res_big <- IDFT(DFT(c1) x GadgetCiphertext[0])
62    module.vec_znx_idft_tmp_a(&mut res_big, &mut res_dft, cols);
63
64    // res[0] = normalize(c0 + c1_dft x GadgetCiphertext[0])
65    module.vec_znx_big_normalize(log_base2k, res.at_mut(0), &res_big, tmp_bytes_vmp_apply_dft);
66
67    // res_dft <- DFT(c1) x GadgetCiphertext[1]
68    module.vmp_apply_dft_to_dft(&mut res_dft, &c1_dft, &b.value[1], tmp_bytes_vmp_apply_dft);
69
70    // res_big <- IDFT(DFT(c1) x GadgetCiphertext[1])
71    module.vec_znx_idft_tmp_a(&mut res_big, &mut res_dft, cols);
72
73    // res[1] = normalize(c1_dft x GadgetCiphertext[1])
74    module.vec_znx_big_normalize(log_base2k, res.at_mut(1), &res_big, tmp_bytes_vmp_apply_dft);
75}