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use std::io;
use std::marker::PhantomData;
use ff::PrimeField;
use crate::{Index, LinearCombination, Variable};
/// Computations are expressed in terms of arithmetic circuits, in particular
/// rank-1 quadratic constraint systems. The `Circuit` trait represents a
/// circuit that can be synthesized. The `synthesize` method is called during
/// CRS generation and during proving.
pub trait Circuit<Scalar: PrimeField> {
/// Synthesize the circuit into a rank-1 quadratic constraint system.
fn synthesize<CS: ConstraintSystem<Scalar>>(self, cs: &mut CS) -> Result<(), SynthesisError>;
}
/// This is an error that could occur during circuit synthesis contexts,
/// such as CRS generation, proving or verification.
#[allow(clippy::upper_case_acronyms)]
#[derive(thiserror::Error, Debug)]
pub enum SynthesisError {
/// During synthesis, we lacked knowledge of a variable assignment.
#[error("an assignment for a variable could not be computed")]
AssignmentMissing,
/// During synthesis, we divided by zero.
#[error("division by zero")]
DivisionByZero,
/// During synthesis, we constructed an unsatisfiable constraint system.
#[error("unsatisfiable constraint system")]
Unsatisfiable,
/// During synthesis, our polynomials ended up being too high of degree
#[error("polynomial degree is too large")]
PolynomialDegreeTooLarge,
/// During proof generation, we encountered an identity in the CRS
#[error("encountered an identity element in the CRS")]
UnexpectedIdentity,
/// During proof generation, we encountered an I/O error with the CRS
#[error("encountered an I/O error: {0}")]
IoError(#[from] io::Error),
/// During verification, our verifying key was malformed.
#[error("malformed verifying key")]
MalformedVerifyingKey,
/// During CRS generation, we observed an unconstrained auxiliary variable
#[error("auxiliary variable was unconstrained")]
UnconstrainedVariable,
/// During GPU multiexp/fft, some GPU related error happened
#[error("attempted to aggregate malformed proofs: {0}")]
MalformedProofs(String),
#[error("malformed SRS")]
MalformedSrs,
#[error("non power of two proofs given for aggregation")]
NonPowerOfTwo,
#[error("incompatible vector length: {0}")]
IncompatibleLengthVector(String),
#[error("invalid pairing")]
InvalidPairing,
}
/// Represents a constraint system which can have new variables
/// allocated and constrains between them formed.
pub trait ConstraintSystem<Scalar: PrimeField>: Sized + Send {
/// Represents the type of the "root" of this constraint system
/// so that nested namespaces can minimize indirection.
type Root: ConstraintSystem<Scalar>;
fn new() -> Self {
unimplemented!(
"ConstraintSystem::new must be implemented for extensible types implementing ConstraintSystem"
);
}
/// Return the "one" input variable
fn one() -> Variable {
Variable::new_unchecked(Index::Input(0))
}
/// Allocate a private variable in the constraint system. The provided function is used to
/// determine the assignment of the variable. The given `annotation` function is invoked
/// in testing contexts in order to derive a unique name for this variable in the current
/// namespace.
fn alloc<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>;
/// Allocate a public variable in the constraint system. The provided function is used to
/// determine the assignment of the variable.
fn alloc_input<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>;
/// Enforce that `A` * `B` = `C`. The `annotation` function is invoked in testing contexts
/// in order to derive a unique name for the constraint in the current namespace.
fn enforce<A, AR, LA, LB, LC>(&mut self, annotation: A, a: LA, b: LB, c: LC)
where
A: FnOnce() -> AR,
AR: Into<String>,
LA: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LB: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LC: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>;
/// Create a new (sub)namespace and enter into it. Not intended
/// for downstream use; use `namespace` instead.
fn push_namespace<NR, N>(&mut self, name_fn: N)
where
NR: Into<String>,
N: FnOnce() -> NR;
/// Exit out of the existing namespace. Not intended for
/// downstream use; use `namespace` instead.
fn pop_namespace(&mut self);
/// Gets the "root" constraint system, bypassing the namespacing.
/// Not intended for downstream use; use `namespace` instead.
fn get_root(&mut self) -> &mut Self::Root;
/// Begin a namespace for this constraint system.
fn namespace<NR, N>(&mut self, name_fn: N) -> Namespace<'_, Scalar, Self::Root>
where
NR: Into<String>,
N: FnOnce() -> NR,
{
self.get_root().push_namespace(name_fn);
Namespace(self.get_root(), Default::default())
}
/// Most implementations of ConstraintSystem are not 'extensible': they won't implement a specialized
/// version of `extend` and should therefore also keep the default implementation of `is_extensible`
/// so callers which optionally make use of `extend` can know to avoid relying on it when unimplemented.
fn is_extensible() -> bool {
false
}
/// Extend concatenates thew `other` constraint systems to the receiver, modifying the receiver, whose
/// inputs, allocated variables, and constraints will precede those of the `other` constraint system.
/// The primary use case for this is parallel synthesis of circuits which can be decomposed into
/// entirely independent sub-circuits. Each can be synthesized in its own thread, then the
/// original `ConstraintSystem` can be extended with each, in the same order they would have
/// been synthesized sequentially.
fn extend(&mut self, _other: &Self) {
unimplemented!(
"ConstraintSystem::extend must be implemented for types implementing ConstraintSystem"
);
}
/// Determines if the current `ConstraintSystem` instance is a witness generator.
/// ConstraintSystems that are witness generators need not assemble the actual constraints. Rather, they exist only
/// to efficiently create a witness.
///
/// # Returns
///
/// * `false` - By default, a `ConstraintSystem` is not a witness generator.
fn is_witness_generator(&self) -> bool {
false
}
/// Extend the inputs of the `ConstraintSystem`.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn extend_inputs(&mut self, _new_inputs: &[Scalar]) {
assert!(self.is_witness_generator());
unimplemented!()
}
/// Extend the auxiliary inputs of the `ConstraintSystem`.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn extend_aux(&mut self, _new_aux: &[Scalar]) {
assert!(self.is_witness_generator());
unimplemented!()
}
/// Allocate empty space for the auxiliary inputs and the main inputs of the `ConstraintSystem`.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn allocate_empty(
&mut self,
_aux_n: usize,
_inputs_n: usize,
) -> (&mut [Scalar], &mut [Scalar]) {
// This method should only ever be called on witness generators.
assert!(self.is_witness_generator());
unimplemented!()
}
/// Allocate empty space for the main inputs of the `ConstraintSystem`.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn allocate_empty_inputs(&mut self, _n: usize) -> &mut [Scalar] {
// This method should only ever be called on witness generators.
assert!(self.is_witness_generator());
unimplemented!()
}
/// Allocate empty space for the auxiliary inputs of the `ConstraintSystem`.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn allocate_empty_aux(&mut self, _n: usize) -> &mut [Scalar] {
// This method should only ever be called on witness generators.
assert!(self.is_witness_generator());
unimplemented!()
}
/// Returns the constraint system's inputs as a slice of `Scalar`s.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn inputs_slice(&self) -> &[Scalar] {
assert!(self.is_witness_generator());
unimplemented!()
}
/// Returns the constraint system's aux witness as a slice of `Scalar`s.
///
/// # Panics
///
/// Panics if called on a `ConstraintSystem` that is not a witness generator.
fn aux_slice(&self) -> &[Scalar] {
assert!(self.is_witness_generator());
unimplemented!()
}
}
/// This is a "namespaced" constraint system which borrows a constraint system (pushing
/// a namespace context) and, when dropped, pops out of the namespace context.
pub struct Namespace<'a, Scalar: PrimeField, CS: ConstraintSystem<Scalar>>(
&'a mut CS,
PhantomData<Scalar>,
);
impl<'cs, Scalar: PrimeField, CS: ConstraintSystem<Scalar>> ConstraintSystem<Scalar>
for Namespace<'cs, Scalar, CS>
{
type Root = CS::Root;
fn one() -> Variable {
CS::one()
}
fn alloc<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>,
{
self.0.alloc(annotation, f)
}
fn alloc_input<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>,
{
self.0.alloc_input(annotation, f)
}
fn enforce<A, AR, LA, LB, LC>(&mut self, annotation: A, a: LA, b: LB, c: LC)
where
A: FnOnce() -> AR,
AR: Into<String>,
LA: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LB: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LC: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
{
self.0.enforce(annotation, a, b, c)
}
// Downstream users who use `namespace` will never interact with these
// functions and they will never be invoked because the namespace is
// never a root constraint system.
fn push_namespace<NR, N>(&mut self, _: N)
where
NR: Into<String>,
N: FnOnce() -> NR,
{
panic!("only the root's push_namespace should be called");
}
fn pop_namespace(&mut self) {
panic!("only the root's pop_namespace should be called");
}
fn get_root(&mut self) -> &mut Self::Root {
self.0.get_root()
}
fn is_witness_generator(&self) -> bool {
self.0.is_witness_generator()
}
fn extend_inputs(&mut self, new_inputs: &[Scalar]) {
self.0.extend_inputs(new_inputs)
}
fn extend_aux(&mut self, new_aux: &[Scalar]) {
self.0.extend_aux(new_aux)
}
fn allocate_empty(&mut self, aux_n: usize, inputs_n: usize) -> (&mut [Scalar], &mut [Scalar]) {
self.0.allocate_empty(aux_n, inputs_n)
}
fn inputs_slice(&self) -> &[Scalar] {
self.0.inputs_slice()
}
fn aux_slice(&self) -> &[Scalar] {
self.0.aux_slice()
}
}
impl<'a, Scalar: PrimeField, CS: ConstraintSystem<Scalar>> Drop for Namespace<'a, Scalar, CS> {
fn drop(&mut self) {
self.get_root().pop_namespace()
}
}
/// Convenience implementation of ConstraintSystem<Scalar> for mutable references to
/// constraint systems.
impl<'cs, Scalar: PrimeField, CS: ConstraintSystem<Scalar>> ConstraintSystem<Scalar>
for &'cs mut CS
{
type Root = CS::Root;
fn one() -> Variable {
CS::one()
}
fn alloc<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>,
{
(**self).alloc(annotation, f)
}
fn alloc_input<F, A, AR>(&mut self, annotation: A, f: F) -> Result<Variable, SynthesisError>
where
F: FnOnce() -> Result<Scalar, SynthesisError>,
A: FnOnce() -> AR,
AR: Into<String>,
{
(**self).alloc_input(annotation, f)
}
fn enforce<A, AR, LA, LB, LC>(&mut self, annotation: A, a: LA, b: LB, c: LC)
where
A: FnOnce() -> AR,
AR: Into<String>,
LA: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LB: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
LC: FnOnce(LinearCombination<Scalar>) -> LinearCombination<Scalar>,
{
(**self).enforce(annotation, a, b, c)
}
fn push_namespace<NR, N>(&mut self, name_fn: N)
where
NR: Into<String>,
N: FnOnce() -> NR,
{
(**self).push_namespace(name_fn)
}
fn pop_namespace(&mut self) {
(**self).pop_namespace()
}
fn get_root(&mut self) -> &mut Self::Root {
(**self).get_root()
}
fn namespace<NR, N>(&mut self, name_fn: N) -> Namespace<'_, Scalar, Self::Root>
where
NR: Into<String>,
N: FnOnce() -> NR,
{
(**self).namespace(name_fn)
}
fn is_extensible() -> bool {
CS::is_extensible()
}
fn extend(&mut self, other: &Self) {
(**self).extend(other)
}
fn is_witness_generator(&self) -> bool {
(**self).is_witness_generator()
}
fn extend_inputs(&mut self, new_inputs: &[Scalar]) {
(**self).extend_inputs(new_inputs)
}
fn extend_aux(&mut self, new_aux: &[Scalar]) {
(**self).extend_aux(new_aux)
}
fn allocate_empty(&mut self, aux_n: usize, inputs_n: usize) -> (&mut [Scalar], &mut [Scalar]) {
(**self).allocate_empty(aux_n, inputs_n)
}
fn allocate_empty_inputs(&mut self, n: usize) -> &mut [Scalar] {
(**self).allocate_empty_inputs(n)
}
fn allocate_empty_aux(&mut self, n: usize) -> &mut [Scalar] {
(**self).allocate_empty_aux(n)
}
fn inputs_slice(&self) -> &[Scalar] {
(**self).inputs_slice()
}
fn aux_slice(&self) -> &[Scalar] {
(**self).aux_slice()
}
}