p3_dft/
butterflies.rs

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1use core::mem::MaybeUninit;
2
3use itertools::izip;
4use p3_field::{Field, PackedField, PackedValue};
5
6pub trait Butterfly<F: Field>: Copy + Send + Sync {
7    fn apply<PF: PackedField<Scalar = F>>(&self, x_1: PF, x_2: PF) -> (PF, PF);
8
9    #[inline]
10    fn apply_in_place<PF: PackedField<Scalar = F>>(&self, x_1: &mut PF, x_2: &mut PF) {
11        (*x_1, *x_2) = self.apply(*x_1, *x_2);
12    }
13
14    #[inline]
15    fn apply_to_rows(&self, row_1: &mut [F], row_2: &mut [F]) {
16        let (shorts_1, suffix_1) = F::Packing::pack_slice_with_suffix_mut(row_1);
17        let (shorts_2, suffix_2) = F::Packing::pack_slice_with_suffix_mut(row_2);
18        debug_assert_eq!(shorts_1.len(), shorts_2.len());
19        debug_assert_eq!(suffix_1.len(), suffix_2.len());
20        for (x_1, x_2) in shorts_1.iter_mut().zip(shorts_2) {
21            self.apply_in_place(x_1, x_2);
22        }
23        for (x_1, x_2) in suffix_1.iter_mut().zip(suffix_2) {
24            self.apply_in_place(x_1, x_2);
25        }
26    }
27
28    /// Like `apply_to_rows`, but out-of-place.
29    #[inline]
30    fn apply_to_rows_oop(
31        &self,
32        src_1: &[F],
33        dst_1: &mut [MaybeUninit<F>],
34        src_2: &[F],
35        dst_2: &mut [MaybeUninit<F>],
36    ) {
37        let (src_shorts_1, src_suffix_1) = F::Packing::pack_slice_with_suffix(src_1);
38        let (src_shorts_2, src_suffix_2) = F::Packing::pack_slice_with_suffix(src_2);
39        let (dst_shorts_1, dst_suffix_1) =
40            F::Packing::pack_maybe_uninit_slice_with_suffix_mut(dst_1);
41        let (dst_shorts_2, dst_suffix_2) =
42            F::Packing::pack_maybe_uninit_slice_with_suffix_mut(dst_2);
43        debug_assert_eq!(src_shorts_1.len(), src_shorts_2.len());
44        debug_assert_eq!(src_suffix_1.len(), src_suffix_2.len());
45        debug_assert_eq!(dst_shorts_1.len(), dst_shorts_2.len());
46        debug_assert_eq!(dst_suffix_1.len(), dst_suffix_2.len());
47        for (s_1, s_2, d_1, d_2) in izip!(src_shorts_1, src_shorts_2, dst_shorts_1, dst_shorts_2) {
48            let (res_1, res_2) = self.apply::<F::Packing>(*s_1, *s_2);
49            d_1.write(res_1);
50            d_2.write(res_2);
51        }
52        for (s_1, s_2, d_1, d_2) in izip!(src_suffix_1, src_suffix_2, dst_suffix_1, dst_suffix_2) {
53            let (res_1, res_2) = self.apply::<F>(*s_1, *s_2);
54            d_1.write(res_1);
55            d_2.write(res_2);
56        }
57    }
58}
59
60#[derive(Copy, Clone)]
61pub struct DifButterfly<F>(pub F);
62impl<F: Field> Butterfly<F> for DifButterfly<F> {
63    #[inline]
64    fn apply<PF: PackedField<Scalar = F>>(&self, x_1: PF, x_2: PF) -> (PF, PF) {
65        (x_1 + x_2, (x_1 - x_2) * self.0)
66    }
67}
68
69#[derive(Copy, Clone)]
70pub struct DitButterfly<F>(pub F);
71impl<F: Field> Butterfly<F> for DitButterfly<F> {
72    #[inline]
73    fn apply<PF: PackedField<Scalar = F>>(&self, x_1: PF, x_2: PF) -> (PF, PF) {
74        let x_2_twiddle = x_2 * self.0;
75        (x_1 + x_2_twiddle, x_1 - x_2_twiddle)
76    }
77}
78
79/// Butterfly with twiddle factor 1 (works in either DIT or DIF).
80#[derive(Copy, Clone)]
81pub struct TwiddleFreeButterfly;
82impl<F: Field> Butterfly<F> for TwiddleFreeButterfly {
83    #[inline]
84    fn apply<PF: PackedField<Scalar = F>>(&self, x_1: PF, x_2: PF) -> (PF, PF) {
85        (x_1 + x_2, x_1 - x_2)
86    }
87}
p3_dft/butterflies.rs

p3_dft/
butterflies.rs
