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Save Barycentric Weights in Bit Reverse Order #1071

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7 changes: 4 additions & 3 deletions crates/prover/src/core/backend/cpu/circle.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,7 +100,9 @@ impl PolyOps for CpuBackend {

let (si_i, vi_p): (Vec<_>, Vec<_>) = (0..domain.size())
.map(|i| {
let coset_point = domain.at(i).into_ef::<SecureField>();
let coset_point = domain
.at(bit_reverse_index(i, domain.log_size()))
.into_ef::<SecureField>();
let minus_two_coset_point_y = coset_point.y * SecureField::from(-2);
(
minus_two_coset_point_y
Expand All @@ -118,7 +120,6 @@ impl PolyOps for CpuBackend {
p.into_ef::<SecureField>(),
);

// TODO(Gali): Change weights order to bit-reverse order.
(0..domain.size())
.map(|i| vn_p / (si_i[i] * vi_p[i]))
.collect_vec()
Expand All @@ -129,7 +130,7 @@ impl PolyOps for CpuBackend {
weights: &Col<CpuBackend, SecureField>,
) -> SecureField {
(0..evals.domain.size()).fold(SecureField::zero(), |acc, i| {
acc + (evals.values[bit_reverse_index(i, evals.domain.log_size())] * weights[i])
acc + (evals.values[i] * weights[i])
})
}

Expand Down
35 changes: 17 additions & 18 deletions crates/prover/src/core/backend/simd/circle.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,7 @@ impl PolyOps for SimdBackend {
p: CirclePoint<SecureField>,
) -> Col<SimdBackend, SecureField> {
let domain = coset.circle_domain();
let log_size = domain.log_size();
let weights_vec_len = domain.size().div_ceil(N_LANES);
if weights_vec_len == 1 {
return Col::<SimdBackend, SecureField>::from_iter(CircleEvaluation::<
Expand All @@ -240,11 +241,12 @@ impl PolyOps for SimdBackend {
));
}

let p = p.into_ef::<SecureField>();
let p_0 = domain.at(0).into_ef::<SecureField>();
let si_0 = SecureField::one()
/ ((p_0.y * SecureField::from(-2))
* coset_vanishing_derivative(
Coset::new(CirclePointIndex::generator(), domain.log_size()),
Coset::new(CirclePointIndex::generator(), log_size),
p_0,
));

Expand All @@ -253,8 +255,10 @@ impl PolyOps for SimdBackend {
.map(|i| {
PackedSecureField::from_array(std::array::from_fn(|j| {
point_vanishing(
domain.at(i * N_LANES + j).into_ef::<SecureField>(),
p.into_ef::<SecureField>(),
domain
.at(bit_reverse_index(i * N_LANES + j, log_size))
.into_ef::<SecureField>(),
p,
)
}))
})
Expand All @@ -266,25 +270,21 @@ impl PolyOps for SimdBackend {
};
batch_inverse_in_place(&vi_p, &mut vi_p_inverse);

let vn_p: SecureField = coset_vanishing(
CanonicCoset::new(domain.log_size()).coset,
p.into_ef::<SecureField>(),
);

let si_0_vn_p = PackedSecureField::broadcast(si_0 * vn_p);
let vn_p: SecureField = coset_vanishing(CanonicCoset::new(log_size).coset, p);

// TODO(Gali): Change weights order to bit-reverse order.
// S_i(i) is invariant under G_(n−1) and alternate under J, meaning the S_i(i) values are
// the same for each half coset, and the second half coset values are the conjugate
// of the first half coset values.
let si_i_vn_p = PackedSecureField::from_array(std::array::from_fn(|i| {
if i % 2 == 0 {
si_0 * vn_p
} else {
-si_0 * vn_p
}
}));

let weights: Col<SimdBackend, SecureField> = (0..weights_vec_len)
.map(|i| {
if i < weights_vec_len / 2 {
vi_p_inverse[i] * si_0_vn_p
} else {
vi_p_inverse[i] * -si_0_vn_p
}
})
.map(|i| vi_p_inverse[i] * si_i_vn_p)
.collect();

weights
Expand All @@ -294,7 +294,6 @@ impl PolyOps for SimdBackend {
evals: &CircleEvaluation<SimdBackend, BaseField, BitReversedOrder>,
weights: &Col<SimdBackend, SecureField>,
) -> SecureField {
let evals = evals.clone().bit_reverse();
(0..evals.domain.size().div_ceil(N_LANES))
.fold(PackedSecureField::zero(), |acc, i| {
acc + (weights.data[i] * evals.values.data[i])
Expand Down
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