Skip to content

Commit

Permalink
Merge pull request #755 from zcash/lookup-errors
Browse files Browse the repository at this point in the history 
`plonk::Error::TableError`: Better lookup errors
  • Loading branch information
@daira
daira authored Apr 4, 2023
2 parents 2633567 + 72ce521 commit 5678a50
Show file tree
Hide file tree
Showing 7 changed files with 470 additions and 144 deletions.
9 changes: 6 additions & 3 deletions halo2_proofs/src/circuit.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,9 @@ pub mod floor_planner;
pub use floor_planner::single_pass::SimpleFloorPlanner;

pub mod layouter;
mod table_layouter;

pub use table_layouter::TableLayouter;

/// A chip implements a set of instructions that can be used by gadgets.
///
Expand Down Expand Up @@ -365,11 +368,11 @@ impl<'r, F: Field> Region<'r, F> {
/// A lookup table in the circuit.
#[derive(Debug)]
pub struct Table<'r, F: Field> {
table: &'r mut dyn layouter::TableLayouter<F>,
table: &'r mut dyn TableLayouter<F>,
}

impl<'r, F: Field> From<&'r mut dyn layouter::TableLayouter<F>> for Table<'r, F> {
fn from(table: &'r mut dyn layouter::TableLayouter<F>) -> Self {
impl<'r, F: Field> From<&'r mut dyn TableLayouter<F>> for Table<'r, F> {
fn from(table: &'r mut dyn TableLayouter<F>) -> Self {
Table { table }
}
}
Expand Down
104 changes: 4 additions & 100 deletions halo2_proofs/src/circuit/floor_planner/single_pass.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,9 @@ use ff::Field;

use crate::{
circuit::{
layouter::{RegionColumn, RegionLayouter, RegionShape, TableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, Value,
layouter::{RegionColumn, RegionLayouter, RegionShape},
table_layouter::{compute_table_lengths, SimpleTableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, TableLayouter, Value,
},
plonk::{
Advice, Any, Assigned, Assignment, Circuit, Column, Error, Fixed, FloorPlanner, Instance,
Expand Down Expand Up @@ -165,24 +166,7 @@ impl<'a, F: Field, CS: Assignment<F> + 'a> Layouter<F> for SingleChipLayouter<'a

// Check that all table columns have the same length `first_unused`,
// and all cells up to that length are assigned.
let first_unused = {
match default_and_assigned
.values()
.map(|(_, assigned)| {
if assigned.iter().all(|b| *b) {
Some(assigned.len())
} else {
None
}
})
.reduce(|acc, item| match (acc, item) {
(Some(a), Some(b)) if a == b => Some(a),
_ => None,
}) {
Some(Some(len)) => len,
_ => return Err(Error::Synthesis), // TODO better error
}
};
let first_unused = compute_table_lengths(&default_and_assigned)?;

// Record these columns so that we can prevent them from being used again.
for column in default_and_assigned.keys() {
Expand Down Expand Up @@ -378,86 +362,6 @@ impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> RegionLayouter<F>
}
}

/// The default value to fill a table column with.
///
/// - The outer `Option` tracks whether the value in row 0 of the table column has been
/// assigned yet. This will always be `Some` once a valid table has been completely
/// assigned.
/// - The inner `Value` tracks whether the underlying `Assignment` is evaluating
/// witnesses or not.
type DefaultTableValue<F> = Option<Value<Assigned<F>>>;

pub(crate) struct SimpleTableLayouter<'r, 'a, F: Field, CS: Assignment<F> + 'a> {
cs: &'a mut CS,
used_columns: &'r [TableColumn],
// maps from a fixed column to a pair (default value, vector saying which rows are assigned)
pub(crate) default_and_assigned: HashMap<TableColumn, (DefaultTableValue<F>, Vec<bool>)>,
}

impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> fmt::Debug for SimpleTableLayouter<'r, 'a, F, CS> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SimpleTableLayouter")
.field("used_columns", &self.used_columns)
.field("default_and_assigned", &self.default_and_assigned)
.finish()
}
}

impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> SimpleTableLayouter<'r, 'a, F, CS> {
pub(crate) fn new(cs: &'a mut CS, used_columns: &'r [TableColumn]) -> Self {
SimpleTableLayouter {
cs,
used_columns,
default_and_assigned: HashMap::default(),
}
}
}

impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> TableLayouter<F>
for SimpleTableLayouter<'r, 'a, F, CS>
{
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error> {
if self.used_columns.contains(&column) {
return Err(Error::Synthesis); // TODO better error
}

let entry = self.default_and_assigned.entry(column).or_default();

let mut value = Value::unknown();
self.cs.assign_fixed(
annotation,
column.inner(),
offset, // tables are always assigned starting at row 0
|| {
let res = to();
value = res;
res
},
)?;

match (entry.0.is_none(), offset) {
// Use the value at offset 0 as the default value for this table column.
(true, 0) => entry.0 = Some(value),
// Since there is already an existing default value for this table column,
// the caller should not be attempting to assign another value at offset 0.
(false, 0) => return Err(Error::Synthesis), // TODO better error
_ => (),
}
if entry.1.len() <= offset {
entry.1.resize(offset + 1, false);
}
entry.1[offset] = true;

Ok(())
}
}

#[cfg(test)]
mod tests {
use pasta_curves::vesta;
Expand Down
25 changes: 4 additions & 21 deletions halo2_proofs/src/circuit/floor_planner/v1.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4,9 +4,9 @@ use ff::Field;

use crate::{
circuit::{
floor_planner::single_pass::SimpleTableLayouter,
layouter::{RegionColumn, RegionLayouter, RegionShape, TableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, Value,
layouter::{RegionColumn, RegionLayouter, RegionShape},
table_layouter::{compute_table_lengths, SimpleTableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, TableLayouter, Value,
},
plonk::{
Advice, Any, Assigned, Assignment, Circuit, Column, Error, Fixed, FloorPlanner, Instance,
Expand Down Expand Up @@ -306,24 +306,7 @@ impl<'p, 'a, F: Field, CS: Assignment<F> + 'a> AssignmentPass<'p, 'a, F, CS> {

// Check that all table columns have the same length `first_unused`,
// and all cells up to that length are assigned.
let first_unused = {
match default_and_assigned
.values()
.map(|(_, assigned)| {
if assigned.iter().all(|b| *b) {
Some(assigned.len())
} else {
None
}
})
.reduce(|acc, item| match (acc, item) {
(Some(a), Some(b)) if a == b => Some(a),
_ => None,
}) {
Some(Some(len)) => len,
_ => return Err(Error::Synthesis), // TODO better error
}
};
let first_unused = compute_table_lengths(&default_and_assigned)?;

// Record these columns so that we can prevent them from being used again.
for column in default_and_assigned.keys() {
Expand Down
21 changes: 2 additions & 19 deletions halo2_proofs/src/circuit/layouter.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,9 @@ use std::fmt;

use ff::Field;

pub use super::table_layouter::TableLayouter;
use super::{Cell, RegionIndex, Value};
use crate::plonk::{Advice, Any, Assigned, Column, Error, Fixed, Instance, Selector, TableColumn};
use crate::plonk::{Advice, Any, Assigned, Column, Error, Fixed, Instance, Selector};

/// Helper trait for implementing a custom [`Layouter`].
///
Expand Down Expand Up @@ -109,24 +110,6 @@ pub trait RegionLayouter<F: Field>: fmt::Debug {
fn constrain_equal(&mut self, left: Cell, right: Cell) -> Result<(), Error>;
}

/// Helper trait for implementing a custom [`Layouter`].
///
/// This trait is used for implementing table assignments.
///
/// [`Layouter`]: super::Layouter
pub trait TableLayouter<F: Field>: fmt::Debug {
/// Assigns a fixed value to a table cell.
///
/// Returns an error if the table cell has already been assigned to.
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error>;
}

/// The shape of a region. For a region at a certain index, we track
/// the set of columns it uses as well as the number of rows it uses.
#[derive(Clone, Debug)]
Expand Down
Loading

0 comments on commit 5678a50

Please sign in to comment.