From 276e09f1fb6c11598a799b815702046de82e5e9f Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Fri, 6 Jul 2018 21:37:18 +0100
Subject: [PATCH] Use ff:ScalarEngine instead of pairing::Engine in bellman
 core

---
 src/domain.rs | 27 +++++++++++++--------------
 src/lib.rs    | 37 ++++++++++++++++++-------------------
 2 files changed, 31 insertions(+), 33 deletions(-)

diff --git a/src/domain.rs b/src/domain.rs
index 26cb4f9..87a8240 100644
--- a/src/domain.rs
+++ b/src/domain.rs
@@ -12,7 +12,6 @@
 
 use ff::{Field, PrimeField, ScalarEngine};
 use group::CurveProjective;
-use pairing::Engine;
 
 use super::{
     SynthesisError
@@ -20,7 +19,7 @@ use super::{
 
 use super::multicore::Worker;
 
-pub struct EvaluationDomain<E: Engine, G: Group<E>> {
+pub struct EvaluationDomain<E: ScalarEngine, G: Group<E>> {
     coeffs: Vec<G>,
     exp: u32,
     omega: E::Fr,
@@ -29,7 +28,7 @@ pub struct EvaluationDomain<E: Engine, G: Group<E>> {
     minv: E::Fr
 }
 
-impl<E: Engine, G: Group<E>> EvaluationDomain<E, G> {
+impl<E: ScalarEngine, G: Group<E>> EvaluationDomain<E, G> {
     pub fn as_ref(&self) -> &[G] {
         &self.coeffs
     }
@@ -224,23 +223,23 @@ impl<G: CurveProjective> Group<G::Engine> for Point<G> {
     }
 }
 
-pub struct Scalar<E: Engine>(pub E::Fr);
+pub struct Scalar<E: ScalarEngine>(pub E::Fr);
 
-impl<E: Engine> PartialEq for Scalar<E> {
+impl<E: ScalarEngine> PartialEq for Scalar<E> {
     fn eq(&self, other: &Scalar<E>) -> bool {
         self.0 == other.0
     }
 }
 
-impl<E: Engine> Copy for Scalar<E> { }
+impl<E: ScalarEngine> Copy for Scalar<E> { }
 
-impl<E: Engine> Clone for Scalar<E> {
+impl<E: ScalarEngine> Clone for Scalar<E> {
     fn clone(&self) -> Scalar<E> {
         *self
     }
 }
 
-impl<E: Engine> Group<E> for Scalar<E> {
+impl<E: ScalarEngine> Group<E> for Scalar<E> {
     fn group_zero() -> Self {
         Scalar(E::Fr::zero())
     }
@@ -255,7 +254,7 @@ impl<E: Engine> Group<E> for Scalar<E> {
     }
 }
 
-fn best_fft<E: Engine, T: Group<E>>(a: &mut [T], worker: &Worker, omega: &E::Fr, log_n: u32)
+fn best_fft<E: ScalarEngine, T: Group<E>>(a: &mut [T], worker: &Worker, omega: &E::Fr, log_n: u32)
 {
     let log_cpus = worker.log_num_cpus();
 
@@ -266,7 +265,7 @@ fn best_fft<E: Engine, T: Group<E>>(a: &mut [T], worker: &Worker, omega: &E::Fr,
     }
 }
 
-fn serial_fft<E: Engine, T: Group<E>>(a: &mut [T], omega: &E::Fr, log_n: u32)
+fn serial_fft<E: ScalarEngine, T: Group<E>>(a: &mut [T], omega: &E::Fr, log_n: u32)
 {
     fn bitreverse(mut n: u32, l: u32) -> u32 {
         let mut r = 0;
@@ -311,7 +310,7 @@ fn serial_fft<E: Engine, T: Group<E>>(a: &mut [T], omega: &E::Fr, log_n: u32)
     }
 }
 
-fn parallel_fft<E: Engine, T: Group<E>>(
+fn parallel_fft<E: ScalarEngine, T: Group<E>>(
     a: &mut [T],
     worker: &Worker,
     omega: &E::Fr,
@@ -377,7 +376,7 @@ fn polynomial_arith() {
     use pairing::bls12_381::Bls12;
     use rand::{self, Rand};
 
-    fn test_mul<E: Engine, R: rand::Rng>(rng: &mut R)
+    fn test_mul<E: ScalarEngine, R: rand::Rng>(rng: &mut R)
     {
         let worker = Worker::new();
 
@@ -424,7 +423,7 @@ fn fft_composition() {
     use pairing::bls12_381::Bls12;
     use rand;
 
-    fn test_comp<E: Engine, R: rand::Rng>(rng: &mut R)
+    fn test_comp<E: ScalarEngine, R: rand::Rng>(rng: &mut R)
     {
         let worker = Worker::new();
 
@@ -463,7 +462,7 @@ fn parallel_fft_consistency() {
     use rand::{self, Rand};
     use std::cmp::min;
 
-    fn test_consistency<E: Engine, R: rand::Rng>(rng: &mut R)
+    fn test_consistency<E: ScalarEngine, R: rand::Rng>(rng: &mut R)
     {
         let worker = Worker::new();
 
diff --git a/src/lib.rs b/src/lib.rs
index 6beaddd..42eccea 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,8 +14,7 @@ mod multiexp;
 pub mod domain;
 pub mod groth16;
 
-use ff::Field;
-use pairing::Engine;
+use ff::{Field, ScalarEngine};
 
 use std::ops::{Add, Sub};
 use std::fmt;
@@ -27,7 +26,7 @@ use std::marker::PhantomData;
 /// 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<E: Engine> {
+pub trait Circuit<E: ScalarEngine> {
     /// Synthesize the circuit into a rank-1 quadratic constraint system
     fn synthesize<CS: ConstraintSystem<E>>(
         self,
@@ -64,21 +63,21 @@ pub enum Index {
 /// This represents a linear combination of some variables, with coefficients
 /// in the scalar field of a pairing-friendly elliptic curve group.
 #[derive(Clone)]
-pub struct LinearCombination<E: Engine>(Vec<(Variable, E::Fr)>);
+pub struct LinearCombination<E: ScalarEngine>(Vec<(Variable, E::Fr)>);
 
-impl<E: Engine> AsRef<[(Variable, E::Fr)]> for LinearCombination<E> {
+impl<E: ScalarEngine> AsRef<[(Variable, E::Fr)]> for LinearCombination<E> {
     fn as_ref(&self) -> &[(Variable, E::Fr)] {
         &self.0
     }
 }
 
-impl<E: Engine> LinearCombination<E> {
+impl<E: ScalarEngine> LinearCombination<E> {
     pub fn zero() -> LinearCombination<E> {
         LinearCombination(vec![])
     }
 }
 
-impl<E: Engine> Add<(E::Fr, Variable)> for LinearCombination<E> {
+impl<E: ScalarEngine> Add<(E::Fr, Variable)> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn add(mut self, (coeff, var): (E::Fr, Variable)) -> LinearCombination<E> {
@@ -88,7 +87,7 @@ impl<E: Engine> Add<(E::Fr, Variable)> for LinearCombination<E> {
     }
 }
 
-impl<E: Engine> Sub<(E::Fr, Variable)> for LinearCombination<E> {
+impl<E: ScalarEngine> Sub<(E::Fr, Variable)> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn sub(self, (mut coeff, var): (E::Fr, Variable)) -> LinearCombination<E> {
@@ -98,7 +97,7 @@ impl<E: Engine> Sub<(E::Fr, Variable)> for LinearCombination<E> {
     }
 }
 
-impl<E: Engine> Add<Variable> for LinearCombination<E> {
+impl<E: ScalarEngine> Add<Variable> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn add(self, other: Variable) -> LinearCombination<E> {
@@ -106,7 +105,7 @@ impl<E: Engine> Add<Variable> for LinearCombination<E> {
     }
 }
 
-impl<E: Engine> Sub<Variable> for LinearCombination<E> {
+impl<E: ScalarEngine> Sub<Variable> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn sub(self, other: Variable) -> LinearCombination<E> {
@@ -114,7 +113,7 @@ impl<E: Engine> Sub<Variable> for LinearCombination<E> {
     }
 }
 
-impl<'a, E: Engine> Add<&'a LinearCombination<E>> for LinearCombination<E> {
+impl<'a, E: ScalarEngine> Add<&'a LinearCombination<E>> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn add(mut self, other: &'a LinearCombination<E>) -> LinearCombination<E> {
@@ -126,7 +125,7 @@ impl<'a, E: Engine> Add<&'a LinearCombination<E>> for LinearCombination<E> {
     }
 }
 
-impl<'a, E: Engine> Sub<&'a LinearCombination<E>> for LinearCombination<E> {
+impl<'a, E: ScalarEngine> Sub<&'a LinearCombination<E>> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn sub(mut self, other: &'a LinearCombination<E>) -> LinearCombination<E> {
@@ -138,7 +137,7 @@ impl<'a, E: Engine> Sub<&'a LinearCombination<E>> for LinearCombination<E> {
     }
 }
 
-impl<'a, E: Engine> Add<(E::Fr, &'a LinearCombination<E>)> for LinearCombination<E> {
+impl<'a, E: ScalarEngine> Add<(E::Fr, &'a LinearCombination<E>)> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn add(mut self, (coeff, other): (E::Fr, &'a LinearCombination<E>)) -> LinearCombination<E> {
@@ -152,7 +151,7 @@ impl<'a, E: Engine> Add<(E::Fr, &'a LinearCombination<E>)> for LinearCombination
     }
 }
 
-impl<'a, E: Engine> Sub<(E::Fr, &'a LinearCombination<E>)> for LinearCombination<E> {
+impl<'a, E: ScalarEngine> Sub<(E::Fr, &'a LinearCombination<E>)> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     fn sub(mut self, (coeff, other): (E::Fr, &'a LinearCombination<E>)) -> LinearCombination<E> {
@@ -222,7 +221,7 @@ impl fmt::Display for SynthesisError {
 
 /// Represents a constraint system which can have new variables
 /// allocated and constrains between them formed.
-pub trait ConstraintSystem<E: Engine>: Sized {
+pub trait ConstraintSystem<E: ScalarEngine>: Sized {
     /// Represents the type of the "root" of this constraint system
     /// so that nested namespaces can minimize indirection.
     type Root: ConstraintSystem<E>;
@@ -294,9 +293,9 @@ pub trait ConstraintSystem<E: Engine>: Sized {
 
 /// 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, E: Engine, CS: ConstraintSystem<E> + 'a>(&'a mut CS, PhantomData<E>);
+pub struct Namespace<'a, E: ScalarEngine, CS: ConstraintSystem<E> + 'a>(&'a mut CS, PhantomData<E>);
 
-impl<'cs, E: Engine, CS: ConstraintSystem<E>> ConstraintSystem<E> for Namespace<'cs, E, CS> {
+impl<'cs, E: ScalarEngine, CS: ConstraintSystem<E>> ConstraintSystem<E> for Namespace<'cs, E, CS> {
     type Root = CS::Root;
 
     fn one() -> Variable {
@@ -359,7 +358,7 @@ impl<'cs, E: Engine, CS: ConstraintSystem<E>> ConstraintSystem<E> for Namespace<
     }
 }
 
-impl<'a, E: Engine, CS: ConstraintSystem<E>> Drop for Namespace<'a, E, CS> {
+impl<'a, E: ScalarEngine, CS: ConstraintSystem<E>> Drop for Namespace<'a, E, CS> {
     fn drop(&mut self) {
         self.get_root().pop_namespace()
     }
@@ -367,7 +366,7 @@ impl<'a, E: Engine, CS: ConstraintSystem<E>> Drop for Namespace<'a, E, CS> {
 
 /// Convenience implementation of ConstraintSystem<E> for mutable references to
 /// constraint systems.
-impl<'cs, E: Engine, CS: ConstraintSystem<E>> ConstraintSystem<E> for &'cs mut CS {
+impl<'cs, E: ScalarEngine, CS: ConstraintSystem<E>> ConstraintSystem<E> for &'cs mut CS {
     type Root = CS::Root;
 
     fn one() -> Variable {