binius_field/arch/portable/byte_sliced/
multiply.rs

1// Copyright 2024-2025 Irreducible Inc.
2use crate::{
3	tower_levels::{TowerLevel, TowerLevelWithArithOps},
4	underlier::WithUnderlier,
5	AESTowerField8b, PackedField,
6};
7
8#[inline(always)]
9pub fn mul<P: PackedField<Scalar = AESTowerField8b>, Level: TowerLevel>(
10	field_element_a: &Level::Data<P>,
11	field_element_b: &Level::Data<P>,
12	destination: &mut Level::Data<P>,
13) {
14	let base_alpha = P::broadcast(AESTowerField8b::from_underlier(0xd3));
15	mul_main::<true, P, Level>(field_element_a, field_element_b, destination, base_alpha);
16}
17
18#[inline(always)]
19pub fn mul_alpha<
20	const WRITING_TO_ZEROS: bool,
21	P: PackedField<Scalar = AESTowerField8b>,
22	Level: TowerLevel,
23>(
24	field_element: &Level::Data<P>,
25	destination: &mut Level::Data<P>,
26	base_alpha: P,
27) {
28	if Level::WIDTH == 1 {
29		if WRITING_TO_ZEROS {
30			destination.as_mut()[0] = field_element[0] * base_alpha;
31		} else {
32			destination.as_mut()[0] += field_element[0] * base_alpha;
33		}
34		return;
35	}
36
37	let (a0, a1) = Level::split(field_element);
38
39	let (result0, result1) = Level::split_mut(destination);
40
41	if WRITING_TO_ZEROS {
42		// Copy a0 into upper half
43		Level::Base::copy_into(a0, result1);
44
45		// Copy a1 into lower half
46		Level::Base::copy_into(a1, result0);
47	} else {
48		// Copy a0 into upper half
49		Level::Base::add_into(a0, result1);
50
51		// Copy a1 into lower half
52		Level::Base::add_into(a1, result0);
53	}
54	// Copy alpha*a1 into upper half
55	mul_alpha::<false, P, Level::Base>(a1, result1, base_alpha);
56}
57
58#[inline(always)]
59pub fn mul_main<
60	const WRITING_TO_ZEROS: bool,
61	P: PackedField<Scalar = AESTowerField8b>,
62	Level: TowerLevel,
63>(
64	field_element_a: &Level::Data<P>,
65	field_element_b: &Level::Data<P>,
66	destination: &mut Level::Data<P>,
67	base_alpha: P,
68) {
69	if Level::WIDTH == 1 {
70		if WRITING_TO_ZEROS {
71			destination.as_mut()[0] = field_element_a[0] * field_element_b[0];
72		} else {
73			destination.as_mut()[0] += field_element_a[0] * field_element_b[0];
74		}
75		return;
76	}
77
78	let (a0, a1) = Level::split(field_element_a);
79
80	let (b0, b1) = Level::split(field_element_b);
81
82	let (result0, result1) = Level::split_mut(destination);
83
84	let xored_halves_a = Level::Base::sum(a0, a1);
85
86	let xored_halves_b = Level::Base::sum(b0, b1);
87
88	let mut z2_z0 = <<Level as TowerLevel>::Base as TowerLevel>::default();
89
90	// z2_z0 = z2
91	mul_main::<true, P, Level::Base>(a1, b1, &mut z2_z0, base_alpha);
92
93	// result1 = z2 * alpha
94	mul_alpha::<WRITING_TO_ZEROS, P, Level::Base>(&z2_z0, result1, base_alpha);
95
96	// z2_z0 = z2 + z0
97	mul_main::<false, P, Level::Base>(a0, b0, &mut z2_z0, base_alpha);
98
99	// result1 = z1 + z2 * alpha
100	mul_main::<false, P, Level::Base>(&xored_halves_a, &xored_halves_b, result1, base_alpha);
101
102	// result1 = z2+ z0+ z1 + z2 * alpha
103	Level::Base::add_into(&z2_z0, result1);
104
105	if WRITING_TO_ZEROS {
106		Level::Base::copy_into(&z2_z0, result0);
107	} else {
108		Level::Base::add_into(&z2_z0, result0);
109	}
110}
binius_field/arch/portable/byte_sliced/multiply.rs

binius_field/arch/portable/byte_sliced/
multiply.rs
