mirror of https://github.com/zcash/orchard.git
82 lines
2.3 KiB
Rust
82 lines
2.3 KiB
Rust
use halo2_proofs::{
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circuit::{AssignedCell, Chip, Layouter},
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plonk::{self, Advice, Column, ConstraintSystem, Constraints, Selector},
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poly::Rotation,
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};
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use pasta_curves::pallas;
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use super::AddInstruction;
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#[derive(Clone, Debug)]
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pub(in crate::circuit) struct AddConfig {
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a: Column<Advice>,
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b: Column<Advice>,
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c: Column<Advice>,
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q_add: Selector,
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}
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/// A chip implementing a single addition constraint `c = a + b` on a single row.
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pub(in crate::circuit) struct AddChip {
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config: AddConfig,
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}
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impl Chip<pallas::Base> for AddChip {
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type Config = AddConfig;
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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 AddChip {
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pub(in crate::circuit) fn configure(
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meta: &mut ConstraintSystem<pallas::Base>,
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a: Column<Advice>,
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b: Column<Advice>,
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c: Column<Advice>,
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) -> AddConfig {
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let q_add = meta.selector();
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meta.create_gate("Field element addition: c = a + b", |meta| {
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let q_add = meta.query_selector(q_add);
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let a = meta.query_advice(a, Rotation::cur());
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let b = meta.query_advice(b, Rotation::cur());
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let c = meta.query_advice(c, Rotation::cur());
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Constraints::with_selector(q_add, Some(a + b - c))
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});
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AddConfig { a, b, c, q_add }
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}
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pub(in crate::circuit) fn construct(config: AddConfig) -> Self {
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Self { config }
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}
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}
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impl AddInstruction<pallas::Base> for AddChip {
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fn add(
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&self,
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mut layouter: impl Layouter<pallas::Base>,
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a: &AssignedCell<pallas::Base, pallas::Base>,
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b: &AssignedCell<pallas::Base, pallas::Base>,
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) -> Result<AssignedCell<pallas::Base, pallas::Base>, plonk::Error> {
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layouter.assign_region(
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|| "c = a + b",
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|mut region| {
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self.config.q_add.enable(&mut region, 0)?;
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a.copy_advice(|| "copy a", &mut region, self.config.a, 0)?;
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b.copy_advice(|| "copy b", &mut region, self.config.b, 0)?;
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let scalar_val = a.value().zip(b.value()).map(|(a, b)| a + b);
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region.assign_advice(|| "c", self.config.c, 0, || scalar_val)
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},
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)
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}
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}
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