Move from Field::negate to Neg operator

src/gadgets/lookup.rs

@@ -1,7 +1,7 @@
 //! Window table lookup gadgets.
 
 use ff::{Field, ScalarEngine};
-use std::ops::AddAssign;
+use std::ops::{AddAssign, Neg};
 
 use super::boolean::Boolean;
 use super::num::{AllocatedNum, Num};
@@ -16,8 +16,7 @@ where
     assert_eq!(assignment.len(), 1 << window_size);
 
     for (i, constant) in constants.into_iter().enumerate() {
-        let mut cur = assignment[i];
-        cur.negate();
+        let mut cur = assignment[i].neg();
         cur.add_assign(constant);
         assignment[i] = cur;
         for (j, eval) in assignment.iter_mut().enumerate().skip(i + 1) {
@@ -151,7 +150,7 @@ where
     let y = AllocatedNum::alloc(cs.namespace(|| "y"), || {
         let mut tmp = coords[*i.get()?].1;
         if *bits[2].get_value().get()? {
-            tmp.negate();
+            tmp = tmp.neg();
         }
         Ok(tmp)
     })?;
@@ -281,7 +280,7 @@ mod test {
             assert_eq!(res.0.get_value().unwrap(), points[index].0);
             let mut tmp = points[index].1;
             if c_val {
-                tmp.negate()
+                tmp = tmp.neg()
             }
             assert_eq!(res.1.get_value().unwrap(), tmp);
         }

src/gadgets/num.rs

@@ -417,7 +417,7 @@ mod test {
     use pairing::bls12_381::{Bls12, Fr};
     use rand_core::SeedableRng;
     use rand_xorshift::XorShiftRng;
-    use std::ops::SubAssign;
+    use std::ops::{Neg, SubAssign};
 
     use super::{AllocatedNum, Boolean};
     use crate::gadgets::test::*;
@@ -519,8 +519,7 @@ mod test {
 
     #[test]
     fn test_into_bits_strict() {
-        let mut negone = Fr::one();
-        negone.negate();
+        let negone = Fr::one().neg();
 
         let mut cs = TestConstraintSystem::<Bls12>::new();
 

src/gadgets/test/mod.rs

@@ -6,7 +6,7 @@ use crate::{ConstraintSystem, Index, LinearCombination, SynthesisError, Variable
 
 use std::collections::HashMap;
 use std::fmt::Write;
-use std::ops::{AddAssign, MulAssign};
+use std::ops::{AddAssign, MulAssign, Neg};
 
 use byteorder::{BigEndian, ByteOrder};
 use std::cmp::Ordering;
@@ -152,11 +152,7 @@ impl<E: ScalarEngine> TestConstraintSystem<E> {
     pub fn pretty_print(&self) -> String {
         let mut s = String::new();
 
-        let negone = {
-            let mut tmp = E::Fr::one();
-            tmp.negate();
-            tmp
-        };
+        let negone = E::Fr::one().neg();
 
         let powers_of_two = (0..E::Fr::NUM_BITS)
             .map(|i| E::Fr::from_str("2").unwrap().pow(&[u64::from(i)]))

src/groth16/tests/dummy_engine.rs

@@ -9,7 +9,7 @@ use rand_core::RngCore;
 use std::cmp::Ordering;
 use std::fmt;
 use std::num::Wrapping;
-use std::ops::{Add, AddAssign, Mul, MulAssign, Sub, SubAssign};
+use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
 
 const MODULUS_R: Wrapping<u32> = Wrapping(64513);
 
@@ -22,6 +22,17 @@ impl fmt::Display for Fr {
     }
 }
 
+impl Neg for Fr {
+    type Output = Self;
+
+    fn neg(mut self) -> Self {
+        if !<Fr as Field>::is_zero(&self) {
+            self.0 = MODULUS_R - self.0;
+        }
+        self
+    }
+}
+
 impl<'r> Add<&'r Fr> for Fr {
     type Output = Self;
 
@@ -137,12 +148,6 @@ impl Field for Fr {
         self.0 = (self.0 << 1) % MODULUS_R;
     }
 
-    fn negate(&mut self) {
-        if !<Fr as Field>::is_zero(self) {
-            self.0 = MODULUS_R - self.0;
-        }
-    }
-
     fn inverse(&self) -> Option<Self> {
         if <Fr as Field>::is_zero(self) {
             None
@@ -413,7 +418,7 @@ impl CurveProjective for Fr {
     }
 
     fn negate(&mut self) {
-        <Fr as Field>::negate(self);
+        self.0 = self.neg().0;
     }
 
     fn mul_assign<S: Into<<Self::Scalar as PrimeField>::Repr>>(&mut self, other: S) {
@@ -495,7 +500,7 @@ impl CurveAffine for Fr {
     }
 
     fn negate(&mut self) {
-        <Fr as Field>::negate(self);
+        self.0 = self.neg().0;
     }
 
     fn mul<S: Into<<Self::Scalar as PrimeField>::Repr>>(&self, other: S) -> Self::Projective {

src/lib.rs

@@ -161,7 +161,7 @@ use std::error::Error;
 use std::fmt;
 use std::io;
 use std::marker::PhantomData;
-use std::ops::{Add, MulAssign, Sub};
+use std::ops::{Add, MulAssign, Neg, Sub};
 
 /// Computations are expressed in terms of arithmetic circuits, in particular
 /// rank-1 quadratic constraint systems. The `Circuit` trait represents a
@@ -229,10 +229,8 @@ impl<E: ScalarEngine> Sub<(E::Fr, Variable)> for LinearCombination<E> {
     type Output = LinearCombination<E>;
 
     #[allow(clippy::suspicious_arithmetic_impl)]
-    fn sub(self, (mut coeff, var): (E::Fr, Variable)) -> LinearCombination<E> {
-        coeff.negate();
-
-        self + (coeff, var)
+    fn sub(self, (coeff, var): (E::Fr, Variable)) -> LinearCombination<E> {
+        self + (coeff.neg(), var)
     }
 }