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https://github.com/logos-storage/plonky2.git
synced 2026-02-19 13:23:07 +00:00
Clean low-degree interpolation gate
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wborgeaud
parent
5ea632f2a8
commit
fa29db1dcb
@ -26,38 +26,6 @@ pub(crate) struct LowDegreeInterpolationGate<F: RichField + Extendable<D>, const
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_phantom: PhantomData<F>,
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}
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impl<F: RichField + Extendable<D>, const D: usize> LowDegreeInterpolationGate<F, D> {
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pub fn powers_init(&self, i: usize) -> usize {
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debug_assert!(0 < i && i < self.num_points());
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if i == 1 {
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return self.wire_shift();
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}
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self.end_coeffs() + i - 2
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}
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pub fn powers_eval(&self, i: usize) -> Range<usize> {
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debug_assert!(0 < i && i < self.num_points());
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if i == 1 {
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return self.wires_evaluation_point();
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}
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let start = self.end_coeffs() + self.num_points() - 2 + (i - 2) * D;
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start..start + D
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}
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/// End of wire indices, exclusive.
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fn end(&self) -> usize {
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self.powers_eval(self.num_points() - 1).end
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}
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/// The domain of the points we're interpolating.
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fn coset(&self, shift: F) -> impl Iterator<Item = F> {
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let g = F::primitive_root_of_unity(self.subgroup_bits);
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let size = 1 << self.subgroup_bits;
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// Speed matters here, so we avoid `cyclic_subgroup_coset_known_order` which allocates.
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g.powers().take(size).map(move |x| x * shift)
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}
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}
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impl<F: RichField + Extendable<D>, const D: usize> InterpolationGate<F, D>
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for LowDegreeInterpolationGate<F, D>
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{
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@ -130,6 +98,40 @@ impl<F: RichField + Extendable<D>, const D: usize> InterpolationGate<F, D>
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}
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}
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impl<F: RichField + Extendable<D>, const D: usize> LowDegreeInterpolationGate<F, D> {
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/// `powers_shift(i)` is the wire index of `wire_shift^i`.
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pub fn powers_shift(&self, i: usize) -> usize {
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debug_assert!(0 < i && i < self.num_points());
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if i == 1 {
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return self.wire_shift();
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}
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self.end_coeffs() + i - 2
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}
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/// `powers_evalutation_point(i)` is the wire index of `evalutation_point^i`.
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pub fn powers_evaluation_point(&self, i: usize) -> Range<usize> {
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debug_assert!(0 < i && i < self.num_points());
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if i == 1 {
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return self.wires_evaluation_point();
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}
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let start = self.end_coeffs() + self.num_points() - 2 + (i - 2) * D;
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start..start + D
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}
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/// End of wire indices, exclusive.
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fn end(&self) -> usize {
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self.powers_evaluation_point(self.num_points() - 1).end
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}
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/// The domain of the points we're interpolating.
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fn coset(&self, shift: F) -> impl Iterator<Item = F> {
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let g = F::primitive_root_of_unity(self.subgroup_bits);
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let size = 1 << self.subgroup_bits;
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// Speed matters here, so we avoid `cyclic_subgroup_coset_known_order` which allocates.
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g.powers().take(size).map(move |x| x * shift)
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}
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}
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impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInterpolationGate<F, D> {
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fn id(&self) -> String {
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format!("{:?}<D={}>", self, D)
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@ -142,33 +144,35 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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.map(|i| vars.get_local_ext_algebra(self.wires_coeff(i)))
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.collect::<Vec<_>>();
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let mut powers_init = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_init(i)])
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let mut powers_shift = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_shift(i)])
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.collect::<Vec<_>>();
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powers_init.insert(0, F::Extension::ONE);
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let wire_shift = powers_init[1];
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for i in 2..self.num_points() {
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constraints.push(powers_init[i - 1] * wire_shift - powers_init[i]);
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let shift = powers_shift[0];
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for i in 1..self.num_points() - 1 {
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constraints.push(powers_shift[i - 1] * shift - powers_shift[i]);
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}
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let ocoeffs = coeffs
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powers_shift.insert(0, F::Extension::ONE);
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// `altered_coeffs[i] = c_i * shift^i`, where `c_i` is the original coefficient.
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// Then, `altered(w^i) = original(shift*w^i)`.
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let altered_coeffs = coeffs
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.iter()
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.zip(powers_init)
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.zip(powers_shift)
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.map(|(&c, p)| c.scalar_mul(p))
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.collect::<Vec<_>>();
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let interpolant = PolynomialCoeffsAlgebra::new(coeffs);
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let ointerpolant = PolynomialCoeffsAlgebra::new(ocoeffs);
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let altered_interpolant = PolynomialCoeffsAlgebra::new(altered_coeffs);
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for (i, point) in F::Extension::two_adic_subgroup(self.subgroup_bits)
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.into_iter()
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.enumerate()
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{
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let value = vars.get_local_ext_algebra(self.wires_value(i));
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let computed_value = ointerpolant.eval_base(point);
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let computed_value = altered_interpolant.eval_base(point);
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constraints.extend(&(value - computed_value).to_basefield_array());
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}
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let evaluation_point_powers = (1..self.num_points())
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.map(|i| vars.get_local_ext_algebra(self.powers_eval(i)))
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.map(|i| vars.get_local_ext_algebra(self.powers_evaluation_point(i)))
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.collect::<Vec<_>>();
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let evaluation_point = evaluation_point_powers[0];
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for i in 1..self.num_points() - 1 {
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@ -190,33 +194,36 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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let coeffs = (0..self.num_points())
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.map(|i| vars.get_local_ext(self.wires_coeff(i)))
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.collect::<Vec<_>>();
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let mut powers_init = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_init(i)])
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let mut powers_shift = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_shift(i)])
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.collect::<Vec<_>>();
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powers_init.insert(0, F::ONE);
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let wire_shift = powers_init[1];
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for i in 2..self.num_points() {
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constraints.push(powers_init[i - 1] * wire_shift - powers_init[i]);
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let shift = powers_shift[0];
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for i in 1..self.num_points() - 1 {
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constraints.push(powers_shift[i - 1] * shift - powers_shift[i]);
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}
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let ocoeffs = coeffs
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powers_shift.insert(0, F::ONE);
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// `altered_coeffs[i] = c_i * shift^i`, where `c_i` is the original coefficient.
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// Then, `altered(w^i) = original(shift*w^i)`.
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let altered_coeffs = coeffs
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.iter()
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.zip(powers_init)
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.zip(powers_shift)
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.map(|(&c, p)| c.scalar_mul(p))
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.collect::<Vec<_>>();
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let interpolant = PolynomialCoeffs::new(coeffs);
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let ointerpolant = PolynomialCoeffs::new(ocoeffs);
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let altered_interpolant = PolynomialCoeffs::new(altered_coeffs);
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for (i, point) in F::two_adic_subgroup(self.subgroup_bits)
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.into_iter()
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.enumerate()
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{
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let value = vars.get_local_ext(self.wires_value(i));
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let computed_value = ointerpolant.eval_base(point);
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let computed_value = altered_interpolant.eval_base(point);
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constraints.extend(&(value - computed_value).to_basefield_array());
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}
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let evaluation_point_powers = (1..self.num_points())
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.map(|i| vars.get_local_ext(self.powers_eval(i)))
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.map(|i| vars.get_local_ext(self.powers_evaluation_point(i)))
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.collect::<Vec<_>>();
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let evaluation_point = evaluation_point_powers[0];
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for i in 1..self.num_points() - 1 {
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@ -242,25 +249,28 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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let coeffs = (0..self.num_points())
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.map(|i| vars.get_local_ext_algebra(self.wires_coeff(i)))
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.collect::<Vec<_>>();
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let mut powers_init = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_init(i)])
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let mut powers_shift = (1..self.num_points())
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.map(|i| vars.local_wires[self.powers_shift(i)])
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.collect::<Vec<_>>();
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powers_init.insert(0, builder.one_extension());
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let wire_shift = powers_init[1];
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for i in 2..self.num_points() {
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let shift = powers_shift[0];
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for i in 1..self.num_points() - 1 {
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constraints.push(builder.mul_sub_extension(
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powers_init[i - 1],
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wire_shift,
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powers_init[i],
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powers_shift[i - 1],
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shift,
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powers_shift[i],
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));
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}
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let ocoeffs = coeffs
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powers_shift.insert(0, builder.one_extension());
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// `altered_coeffs[i] = c_i * shift^i`, where `c_i` is the original coefficient.
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// Then, `altered(w^i) = original(shift*w^i)`.
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let altered_coeffs = coeffs
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.iter()
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.zip(powers_init)
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.zip(powers_shift)
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.map(|(&c, p)| builder.scalar_mul_ext_algebra(p, c))
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.collect::<Vec<_>>();
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let interpolant = PolynomialCoeffsExtAlgebraTarget(coeffs);
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let ointerpolant = PolynomialCoeffsExtAlgebraTarget(ocoeffs);
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let altered_interpolant = PolynomialCoeffsExtAlgebraTarget(altered_coeffs);
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for (i, point) in F::Extension::two_adic_subgroup(self.subgroup_bits)
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.into_iter()
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@ -268,7 +278,7 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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{
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let value = vars.get_local_ext_algebra(self.wires_value(i));
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let point = builder.constant_extension(point);
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let computed_value = ointerpolant.eval_scalar(builder, point);
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let computed_value = altered_interpolant.eval_scalar(builder, point);
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constraints.extend(
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&builder
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.sub_ext_algebra(value, computed_value)
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@ -277,7 +287,7 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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}
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let evaluation_point_powers = (1..self.num_points())
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.map(|i| vars.get_local_ext_algebra(self.powers_eval(i)))
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.map(|i| vars.get_local_ext_algebra(self.powers_evaluation_point(i)))
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.collect::<Vec<_>>();
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let evaluation_point = evaluation_point_powers[0];
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for i in 1..self.num_points() - 1 {
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@ -328,8 +338,6 @@ impl<F: RichField + Extendable<D>, const D: usize> Gate<F, D> for LowDegreeInter
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}
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fn degree(&self) -> usize {
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// The highest power of x is `num_points - 1`, and then multiplication by the coefficient
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// adds 1.
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2
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}
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@ -395,7 +403,7 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F>
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.enumerate()
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.skip(2)
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{
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out_buffer.set_wire(local_wire(self.gate.powers_init(i)), power);
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out_buffer.set_wire(local_wire(self.gate.powers_shift(i)), power);
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}
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// Compute the interpolant.
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@ -413,10 +421,15 @@ impl<F: RichField + Extendable<D>, const D: usize> SimpleGenerator<F>
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}
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let evaluation_point = get_local_ext(self.gate.wires_evaluation_point());
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for i in 2..self.gate.num_points() {
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for (i, power) in evaluation_point
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.powers()
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.take(self.gate.num_points())
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.enumerate()
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.skip(2)
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{
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out_buffer.set_extension_target(
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ExtensionTarget::from_range(self.gate_index, self.gate.powers_eval(i)),
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evaluation_point.exp_u64(i as u64),
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ExtensionTarget::from_range(self.gate_index, self.gate.powers_evaluation_point(i)),
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power,
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);
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}
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let evaluation_value = interpolant.eval(evaluation_point);
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