Struct halo2_base::Context

pub struct Context<F: ScalarField> {
    pub context_id: usize,
    pub advice: Vec<Assigned<F>>,
    pub cells_to_lookup: Vec<AssignedValue<F>>,
    pub zero_cell: Option<AssignedValue<F>>,
    pub selector: Vec<bool>,
    pub advice_equality_constraints: Vec<(ContextCell, ContextCell)>,
    pub constant_equality_constraints: Vec<(F, ContextCell)>,
    /* private fields */
}

Represents a single thread of an execution trace.

• We keep the naming Context for historical reasons.

Fields

context_id: usize

Identifier to reference cells from this Context.

advice: Vec<Assigned<F>>

Single column of advice cells.

cells_to_lookup: Vec<AssignedValue<F>>

Vec tracking all cells that lookup is enabled for.

• When there is more than 1 advice column all advice cells will be copied to a single lookup enabled column to perform lookups.

zero_cell: Option<AssignedValue<F>>

Cell that represents the zero value as AssignedValue

selector: Vec<bool>

Vec representing the selector column of this Context accompanying each advice column

• Assumed to have the same length as advice

advice_equality_constraints: Vec<(ContextCell, ContextCell)>

A Vec tracking equality constraints between pairs of Context advice cells.

Assumes both advice cells are in the same Context.

constant_equality_constraints: Vec<(F, ContextCell)>

A Vec tracking pairs equality constraints between Fixed values and Context advice cells.

Assumes the constant and advice cell are in the same Context.

Implementations

impl<F: ScalarField> Context<F>

pub fn new(witness_gen_only: bool, context_id: usize) -> Self

Creates a new Context with the given context_id and witness generation enabled/disabled by the witness_gen_only flag.

• witness_gen_only: flag to determine whether public key generation or only witness generation is being performed.
• context_id: identifier to reference advice cells from this Context later.

pub fn witness_gen_only(&self) -> bool

Returns the witness_gen_only flag of the Context

pub fn assign_cell(&mut self, input: impl Into<QuantumCell<F>>)

Pushes a QuantumCell to the end of the advice column (Vec of advice cells) in this Context.

• input: the cell to be assigned.

pub fn last(&self) -> Option<AssignedValue<F>>

Returns the AssignedValue of the last cell in the advice column of Context or None if advice is empty

pub fn get(&self, offset: isize) -> AssignedValue<F>

Returns the AssignedValue of the cell at the given offset in the advice column of Context

• offset: the offset of the cell to be fetched
  • offset may be negative indexing from the end of the column (e.g., -1 is the last cell)
• Assumes offset is a valid index in advice;
  • 0 <= offset < advice.len() (or advice.len() + offset >= 0 if offset is negative)

pub fn constrain_equal(&mut self, a: &AssignedValue<F>, b: &AssignedValue<F>)

Creates an equality constraint between two advice cells.

• a: the first advice cell to be constrained equal
• b: the second advice cell to be constrained equal
• Assumes both cells are advice cells

pub fn assign_region<Q>(
    &mut self,
    inputs: impl IntoIterator<Item = Q>,
    gate_offsets: impl IntoIterator<Item = isize>
)where
    Q: Into<QuantumCell<F>>,

Pushes multiple advice cells to the advice column of Context and enables them by enabling the corresponding selector specified in gate_offset.

• inputs: Iterator that specifies the cells to be assigned
• gate_offsets: specifies relative offset from current position to enable selector for the gate (e.g., 0 is inputs[0]).
  • offset may be negative indexing from the end of the column (e.g., -1 is the last previously assigned cell)

pub fn assign_region_last<Q>(
    &mut self,
    inputs: impl IntoIterator<Item = Q>,
    gate_offsets: impl IntoIterator<Item = isize>
) -> AssignedValue<F>where
    Q: Into<QuantumCell<F>>,

Pushes multiple advice cells to the advice column of Context and enables them by enabling the corresponding selector specified in gate_offset and returns the last assigned cell.

Assumes gate_offsets is the same length as inputs

Returns the last assigned cell

• inputs: Iterator that specifies the cells to be assigned
• gate_offsets: specifies indices to enable selector for the gate; assume gate_offsets is sorted in increasing order
  • offset may be negative indexing from the end of the column (e.g., -1 is the last cell)

pub fn assign_region_smart<Q>(
    &mut self,
    inputs: impl IntoIterator<Item = Q>,
    gate_offsets: impl IntoIterator<Item = isize>,
    equality_offsets: impl IntoIterator<Item = (isize, isize)>,
    external_equality: impl IntoIterator<Item = (Option<ContextCell>, isize)>
)where
    Q: Into<QuantumCell<F>>,

Pushes multiple advice cells to the advice column of Context and enables them by enabling the corresponding selector specified in gate_offset.

Allows for the specification of equality constraints between cells at equality_offsets within the advice column and external advice cells specified in external_equality (e.g, Fixed column).

• gate_offsets: specifies indices to enable selector for the gate;
  • offset may be negative indexing from the end of the column (e.g., -1 is the last cell)
• equality_offsets: specifies pairs of indices to constrain equality
• external_equality: specifies an existing cell to constrain equality with the cell at a certain index

pub fn assign_witnesses(
    &mut self,
    witnesses: impl IntoIterator<Item = F>
) -> Vec<AssignedValue<F>>

Assigns a region of witness cells in an iterator and returns a Vec of assigned cells.

• witnesses: Iterator that specifies the cells to be assigned

pub fn load_witness(&mut self, witness: F) -> AssignedValue<F>

Assigns a witness value and returns the corresponding assigned cell.

• witness: the witness value to be assigned

pub fn load_constant(&mut self, c: F) -> AssignedValue<F>

Assigns a constant value and returns the corresponding assigned cell.

• c: the constant value to be assigned

pub fn load_zero(&mut self) -> AssignedValue<F>

Assigns the 0 value to a new cell or returns a previously assigned zero cell from zero_cell.

Trait Implementations

impl<F: Clone + ScalarField> Clone for Context<F>

fn clone(&self) -> Context<F>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<F: Debug + ScalarField> Debug for Context<F>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.