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use crate::{prelude::*, Vec};
use ark_ff::Field;
use ark_relations::r1cs::SynthesisError;
/// Specifies how to generate constraints that check for equality for two
/// variables of type `Self`.
pub trait EqGadget<F: Field> {
/// Output a `Boolean` value representing whether `self.value() ==
/// other.value()`.
fn is_eq(&self, other: &Self) -> Result<Boolean<F>, SynthesisError>;
/// Output a `Boolean` value representing whether `self.value() !=
/// other.value()`.
///
/// By default, this is defined as `self.is_eq(other)?.not()`.
fn is_neq(&self, other: &Self) -> Result<Boolean<F>, SynthesisError> {
Ok(self.is_eq(other)?.not())
}
/// If `should_enforce == true`, enforce that `self` and `other` are equal;
/// else, enforce a vacuously true statement.
///
/// A safe default implementation is provided that generates the following
/// constraints: `self.is_eq(other)?.conditional_enforce_equal(&Boolean:
/// :TRUE, should_enforce)`.
///
/// More efficient specialized implementation may be possible; implementors
/// are encouraged to carefully analyze the efficiency and safety of these.
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn conditional_enforce_equal(
&self,
other: &Self,
should_enforce: &Boolean<F>,
) -> Result<(), SynthesisError> {
self.is_eq(&other)?
.conditional_enforce_equal(&Boolean::constant(true), should_enforce)
}
/// Enforce that `self` and `other` are equal.
///
/// A safe default implementation is provided that generates the following
/// constraints: `self.conditional_enforce_equal(other,
/// &Boolean::TRUE)`.
///
/// More efficient specialized implementation may be possible; implementors
/// are encouraged to carefully analyze the efficiency and safety of these.
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn enforce_equal(&self, other: &Self) -> Result<(), SynthesisError> {
self.conditional_enforce_equal(other, &Boolean::constant(true))
}
/// If `should_enforce == true`, enforce that `self` and `other` are *not*
/// equal; else, enforce a vacuously true statement.
///
/// A safe default implementation is provided that generates the following
/// constraints: `self.is_neq(other)?.conditional_enforce_equal(&
/// Boolean::TRUE, should_enforce)`.
///
/// More efficient specialized implementation may be possible; implementors
/// are encouraged to carefully analyze the efficiency and safety of these.
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn conditional_enforce_not_equal(
&self,
other: &Self,
should_enforce: &Boolean<F>,
) -> Result<(), SynthesisError> {
self.is_neq(&other)?
.conditional_enforce_equal(&Boolean::constant(true), should_enforce)
}
/// Enforce that `self` and `other` are *not* equal.
///
/// A safe default implementation is provided that generates the following
/// constraints: `self.conditional_enforce_not_equal(other,
/// &Boolean::TRUE)`.
///
/// More efficient specialized implementation may be possible; implementors
/// are encouraged to carefully analyze the efficiency and safety of these.
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn enforce_not_equal(&self, other: &Self) -> Result<(), SynthesisError> {
self.conditional_enforce_not_equal(other, &Boolean::constant(true))
}
}
impl<T: EqGadget<F> + R1CSVar<F>, F: Field> EqGadget<F> for [T] {
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn is_eq(&self, other: &Self) -> Result<Boolean<F>, SynthesisError> {
assert_eq!(self.len(), other.len());
assert!(!self.is_empty());
let mut results = Vec::with_capacity(self.len());
for (a, b) in self.iter().zip(other) {
results.push(a.is_eq(b)?);
}
Boolean::kary_and(&results)
}
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn conditional_enforce_equal(
&self,
other: &Self,
condition: &Boolean<F>,
) -> Result<(), SynthesisError> {
assert_eq!(self.len(), other.len());
for (a, b) in self.iter().zip(other) {
a.conditional_enforce_equal(b, condition)?;
}
Ok(())
}
#[tracing::instrument(target = "r1cs", skip(self, other))]
fn conditional_enforce_not_equal(
&self,
other: &Self,
should_enforce: &Boolean<F>,
) -> Result<(), SynthesisError> {
assert_eq!(self.len(), other.len());
let some_are_different = self.is_neq(other)?;
if [&some_are_different, should_enforce].is_constant() {
assert!(some_are_different.value().unwrap());
Ok(())
} else {
let cs = [&some_are_different, should_enforce].cs();
cs.enforce_constraint(
some_are_different.lc(),
should_enforce.lc(),
should_enforce.lc(),
)
}
}
}