mirror of https://github.com/zcash/orchard.git
443 lines
15 KiB
Rust
443 lines
15 KiB
Rust
use super::EccInstructions;
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use crate::{
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circuit::gadget::utilities::{
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copy, decompose_running_sum::RunningSumConfig, lookup_range_check::LookupRangeCheckConfig,
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CellValue, UtilitiesInstructions, Var,
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},
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constants::{self, NullifierK, OrchardFixedBasesFull, ValueCommitV},
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primitives::sinsemilla,
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};
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use arrayvec::ArrayVec;
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use group::prime::PrimeCurveAffine;
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use halo2::{
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circuit::{Chip, Layouter},
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plonk::{Advice, Column, ConstraintSystem, Error, Fixed, Selector},
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};
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use pasta_curves::{arithmetic::CurveAffine, pallas};
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pub(super) mod add;
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pub(super) mod add_incomplete;
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pub(super) mod mul;
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pub(super) mod mul_fixed;
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pub(super) mod witness_point;
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/// A curve point represented in affine (x, y) coordinates. Each coordinate is
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/// assigned to a cell.
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#[derive(Clone, Debug)]
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pub struct EccPoint {
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/// x-coordinate
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x: CellValue<pallas::Base>,
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/// y-coordinate
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y: CellValue<pallas::Base>,
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}
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impl EccPoint {
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/// Constructs a point from its coordinates, without checking they are on the curve.
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///
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/// This is an internal API that we only use where we know we have a valid curve point
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/// (specifically inside Sinsemilla).
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pub(in crate::circuit::gadget) fn from_coordinates_unchecked(
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x: CellValue<pallas::Base>,
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y: CellValue<pallas::Base>,
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) -> Self {
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EccPoint { x, y }
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}
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/// Returns the value of this curve point, if known.
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pub fn point(&self) -> Option<pallas::Affine> {
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match (self.x.value(), self.y.value()) {
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(Some(x), Some(y)) => {
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if x == pallas::Base::zero() && y == pallas::Base::zero() {
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Some(pallas::Affine::identity())
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} else {
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Some(pallas::Affine::from_xy(x, y).unwrap())
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}
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}
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_ => None,
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}
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}
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/// The cell containing the affine short-Weierstrass x-coordinate,
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/// or 0 for the zero point.
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pub fn x(&self) -> CellValue<pallas::Base> {
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self.x
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}
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/// The cell containing the affine short-Weierstrass y-coordinate,
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/// or 0 for the zero point.
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pub fn y(&self) -> CellValue<pallas::Base> {
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self.y
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}
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}
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/// Configuration for the ECC chip
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#[derive(Clone, Debug, Eq, PartialEq)]
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#[allow(non_snake_case)]
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pub struct EccConfig {
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/// Advice columns needed by instructions in the ECC chip.
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pub advices: [Column<Advice>; 10],
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/// Coefficients of interpolation polynomials for x-coordinates (used in fixed-base scalar multiplication)
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pub lagrange_coeffs: [Column<Fixed>; constants::H],
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/// Fixed z such that y + z = u^2 some square, and -y + z is a non-square. (Used in fixed-base scalar multiplication)
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pub fixed_z: Column<Fixed>,
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/// Incomplete addition
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pub q_add_incomplete: Selector,
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/// Complete addition
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pub q_add: Selector,
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/// Variable-base scalar multiplication (hi half)
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pub q_mul_hi: Column<Fixed>,
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/// Variable-base scalar multiplication (lo half)
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pub q_mul_lo: Column<Fixed>,
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/// Selector used to enforce boolean decomposition in variable-base scalar mul
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pub q_mul_decompose_var: Selector,
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/// Selector used to enforce switching logic on LSB in variable-base scalar mul
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pub q_mul_lsb: Selector,
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/// Variable-base scalar multiplication (overflow check)
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pub q_mul_overflow: Selector,
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/// Fixed-base full-width scalar multiplication
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pub q_mul_fixed_full: Selector,
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/// Fixed-base signed short scalar multiplication
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pub q_mul_fixed_short: Selector,
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/// Canonicity checks on base field element used as scalar in fixed-base mul
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pub q_mul_fixed_base_field: Selector,
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/// Running sum decomposition of a scalar used in fixed-base mul. This is used
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/// when the scalar is a signed short exponent or a base-field element.
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pub q_mul_fixed_running_sum: Selector,
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/// Witness point
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pub q_point: Selector,
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/// Lookup range check using 10-bit lookup table
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pub lookup_config: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
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/// Running sum decomposition.
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pub running_sum_config: RunningSumConfig<pallas::Base, { constants::FIXED_BASE_WINDOW_SIZE }>,
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}
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/// A chip implementing EccInstructions
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#[derive(Clone, Debug, Eq, PartialEq)]
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pub struct EccChip {
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config: EccConfig,
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}
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impl Chip<pallas::Base> for EccChip {
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type Config = EccConfig;
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type Loaded = ();
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fn config(&self) -> &Self::Config {
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&self.config
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}
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fn loaded(&self) -> &Self::Loaded {
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&()
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}
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}
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impl UtilitiesInstructions<pallas::Base> for EccChip {
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type Var = CellValue<pallas::Base>;
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}
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impl EccChip {
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pub fn construct(config: <Self as Chip<pallas::Base>>::Config) -> Self {
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Self { config }
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}
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/// # Side effects
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///
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/// All columns in `advices` will be equality-enabled.
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#[allow(non_snake_case)]
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pub fn configure(
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meta: &mut ConstraintSystem<pallas::Base>,
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advices: [Column<Advice>; 10],
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lagrange_coeffs: [Column<Fixed>; 8],
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range_check: LookupRangeCheckConfig<pallas::Base, { sinsemilla::K }>,
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) -> <Self as Chip<pallas::Base>>::Config {
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// The following columns need to be equality-enabled for their use in sub-configs:
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//
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// add::Config and add_incomplete::Config:
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// - advices[0]: x_p,
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// - advices[1]: y_p,
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// - advices[2]: x_qr,
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// - advices[3]: y_qr,
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//
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// mul_fixed::Config:
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// - advices[4]: window
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// - advices[5]: u
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//
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// mul_fixed::base_field_element::Config:
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// - [advices[6], advices[7], advices[8]]: canon_advices
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//
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// mul::overflow::Config:
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// - [advices[0], advices[1], advices[2]]: advices
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//
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// mul::incomplete::Config
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// - advices[4]: lambda1
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// - advices[9]: z
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//
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// mul::complete::Config:
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// - advices[9]: z_complete
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//
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// TODO: Refactor away from `impl From<EccConfig> for _` so that sub-configs can
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// equality-enable the columns they need to.
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for column in &advices {
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meta.enable_equality((*column).into());
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}
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let q_mul_fixed_running_sum = meta.selector();
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let running_sum_config =
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RunningSumConfig::configure(meta, q_mul_fixed_running_sum, advices[4]);
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let config = EccConfig {
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advices,
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lagrange_coeffs,
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fixed_z: meta.fixed_column(),
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q_add_incomplete: meta.selector(),
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q_add: meta.selector(),
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q_mul_hi: meta.fixed_column(),
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q_mul_lo: meta.fixed_column(),
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q_mul_decompose_var: meta.selector(),
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q_mul_overflow: meta.selector(),
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q_mul_lsb: meta.selector(),
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q_mul_fixed_full: meta.selector(),
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q_mul_fixed_short: meta.selector(),
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q_mul_fixed_base_field: meta.selector(),
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q_mul_fixed_running_sum,
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q_point: meta.selector(),
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lookup_config: range_check,
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running_sum_config,
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};
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// Create witness point gate
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{
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let config: witness_point::Config = (&config).into();
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config.create_gate(meta);
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}
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// Create incomplete point addition gate
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{
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let config: add_incomplete::Config = (&config).into();
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config.create_gate(meta);
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}
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// Create complete point addition gate
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{
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let add_config: add::Config = (&config).into();
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add_config.create_gate(meta);
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}
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// Create variable-base scalar mul gates
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{
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let mul_config: mul::Config = (&config).into();
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mul_config.create_gate(meta);
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}
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// Create gate that is used both in fixed-base mul using a short signed exponent,
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// and fixed-base mul using a base field element.
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{
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// The const generic does not matter when creating gates.
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let mul_fixed_config: mul_fixed::Config<{ constants::NUM_WINDOWS }> = (&config).into();
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mul_fixed_config.running_sum_coords_gate(meta);
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}
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// Create gate that is only used in full-width fixed-base scalar mul.
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{
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let mul_fixed_full_config: mul_fixed::full_width::Config = (&config).into();
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mul_fixed_full_config.create_gate(meta);
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}
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// Create gate that is only used in short fixed-base scalar mul.
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{
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let short_config: mul_fixed::short::Config = (&config).into();
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short_config.create_gate(meta);
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}
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// Create gate that is only used in fixed-base mul using a base field element.
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{
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let base_field_config: mul_fixed::base_field_elem::Config = (&config).into();
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base_field_config.create_gate(meta);
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}
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config
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}
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}
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/// A full-width scalar used for fixed-base scalar multiplication.
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/// This is decomposed into 85 3-bit windows in little-endian order,
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/// i.e. `windows` = [k_0, k_1, ..., k_84] (for a 255-bit scalar)
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/// where `scalar = k_0 + k_1 * (2^3) + ... + k_84 * (2^3)^84` and
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/// each `k_i` is in the range [0..2^3).
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#[derive(Clone, Debug)]
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pub struct EccScalarFixed {
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value: Option<pallas::Scalar>,
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windows: ArrayVec<CellValue<pallas::Base>, { constants::NUM_WINDOWS }>,
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}
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/// A signed short scalar used for fixed-base scalar multiplication.
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/// A short scalar must have magnitude in the range [0..2^64), with
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/// a sign of either 1 or -1.
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/// This is decomposed into 3-bit windows in little-endian order
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/// using a running sum `z`, where z_{i+1} = (z_i - a_i) / (2^3)
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/// for element α = a_0 + (2^3) a_1 + ... + (2^{3(n-1)}) a_{n-1}.
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/// Each `a_i` is in the range [0..2^3).
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///
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/// `windows` = [k_0, k_1, ..., k_21] (for a 64-bit magnitude)
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/// where `scalar = k_0 + k_1 * (2^3) + ... + k_84 * (2^3)^84` and
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/// each `k_i` is in the range [0..2^3).
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/// k_21 must be a single bit, i.e. 0 or 1.
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#[derive(Clone, Debug)]
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pub struct EccScalarFixedShort {
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magnitude: CellValue<pallas::Base>,
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sign: CellValue<pallas::Base>,
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running_sum: ArrayVec<CellValue<pallas::Base>, { constants::NUM_WINDOWS_SHORT }>,
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}
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/// A base field element used for fixed-base scalar multiplication.
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/// This is decomposed into 3-bit windows in little-endian order
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/// using a running sum `z`, where z_{i+1} = (z_i - a_i) / (2^3)
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/// for element α = a_0 + (2^3) a_1 + ... + (2^{3(n-1)}) a_{n-1}.
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/// Each `a_i` is in the range [0..2^3).
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///
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/// `windows` = [z_1, ..., z_85], where we expect z_85 = 0.
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/// Since z_0 is initialized as the scalar α, we store it as
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/// `base_field_elem`.
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#[derive(Clone, Debug)]
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struct EccBaseFieldElemFixed {
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base_field_elem: CellValue<pallas::Base>,
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running_sum: ArrayVec<CellValue<pallas::Base>, { constants::NUM_WINDOWS }>,
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}
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impl EccBaseFieldElemFixed {
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fn base_field_elem(&self) -> CellValue<pallas::Base> {
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self.base_field_elem
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}
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}
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impl EccInstructions<pallas::Affine> for EccChip {
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type ScalarFixed = EccScalarFixed;
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type ScalarFixedShort = EccScalarFixedShort;
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type ScalarVar = CellValue<pallas::Base>;
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type Point = EccPoint;
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type X = CellValue<pallas::Base>;
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type FixedPoints = OrchardFixedBasesFull;
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type FixedPointsBaseField = NullifierK;
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type FixedPointsShort = ValueCommitV;
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fn constrain_equal(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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a: &Self::Point,
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b: &Self::Point,
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) -> Result<(), Error> {
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layouter.assign_region(
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|| "constrain equal",
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|mut region| {
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// Constrain x-coordinates
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region.constrain_equal(a.x().cell(), b.x().cell())?;
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// Constrain x-coordinates
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region.constrain_equal(a.y().cell(), b.y().cell())
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},
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)
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}
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fn witness_point(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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value: Option<pallas::Affine>,
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) -> Result<Self::Point, Error> {
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let config: witness_point::Config = self.config().into();
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layouter.assign_region(
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|| "witness point",
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|mut region| config.assign_region(value, 0, &mut region),
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)
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}
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fn extract_p(point: &Self::Point) -> &Self::X {
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&point.x
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}
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fn add_incomplete(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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a: &Self::Point,
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b: &Self::Point,
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) -> Result<Self::Point, Error> {
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let config: add_incomplete::Config = self.config().into();
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layouter.assign_region(
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|| "incomplete point addition",
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|mut region| config.assign_region(a, b, 0, &mut region),
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)
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}
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fn add(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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a: &Self::Point,
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b: &Self::Point,
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) -> Result<Self::Point, Error> {
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let config: add::Config = self.config().into();
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layouter.assign_region(
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|| "complete point addition",
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|mut region| config.assign_region(a, b, 0, &mut region),
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)
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}
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fn mul(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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scalar: &Self::Var,
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base: &Self::Point,
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) -> Result<(Self::Point, Self::ScalarVar), Error> {
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let config: mul::Config = self.config().into();
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config.assign(
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layouter.namespace(|| "variable-base scalar mul"),
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*scalar,
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base,
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)
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}
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fn mul_fixed(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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scalar: Option<pallas::Scalar>,
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base: &Self::FixedPoints,
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) -> Result<(Self::Point, Self::ScalarFixed), Error> {
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let config: mul_fixed::full_width::Config = self.config().into();
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config.assign(
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layouter.namespace(|| format!("fixed-base mul of {:?}", base)),
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scalar,
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*base,
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)
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}
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fn mul_fixed_short(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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magnitude_sign: (CellValue<pallas::Base>, CellValue<pallas::Base>),
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base: &Self::FixedPointsShort,
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) -> Result<(Self::Point, Self::ScalarFixedShort), Error> {
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let config: mul_fixed::short::Config = self.config().into();
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config.assign(
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layouter.namespace(|| format!("short fixed-base mul of {:?}", base)),
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magnitude_sign,
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base,
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)
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}
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fn mul_fixed_base_field_elem(
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&self,
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layouter: &mut impl Layouter<pallas::Base>,
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base_field_elem: CellValue<pallas::Base>,
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base: &Self::FixedPointsBaseField,
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) -> Result<Self::Point, Error> {
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let config: mul_fixed::base_field_elem::Config = self.config().into();
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config.assign(
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layouter.namespace(|| format!("base-field elem fixed-base mul of {:?}", base)),
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base_field_elem,
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*base,
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)
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}
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}
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