Optimizations to field and curve arithmetic

bls12_381/src/fields/fq2.rs

@@ -21,7 +21,22 @@ impl Fp2Config for Fq2Config {
     ];
 
     #[inline(always)]
-    fn mul_fp_by_nonresidue(fp: &Self::Fp) -> Self::Fp {
-        -(*fp)
+    fn mul_fp_by_nonresidue_in_place(fp: &mut Self::Fp) -> &mut Self::Fp {
+        fp.neg_in_place()
+    }
+
+    #[inline(always)]
+    fn sub_and_mul_fp_by_nonresidue(y: &mut Self::Fp, x: &Self::Fp) {
+        *y += x;
+    }
+
+    #[inline(always)]
+    fn add_and_mul_fp_by_nonresidue_plus_one(y: &mut Self::Fp, x: &Self::Fp) {
+        *y = *x;
+    }
+
+    fn add_and_mul_fp_by_nonresidue_in_place(y: &mut Self::Fp, x: &Self::Fp) {
+        y.neg_in_place();
+        *y += x;
     }
 }

bls12_381/src/fields/fq6.rs

@@ -82,11 +82,10 @@ impl Fp6Config for Fq6Config {
 
     /// Multiply this element by the quadratic nonresidue 1 + u.
     /// Make this generic.
-    fn mul_fp2_by_nonresidue(fe: &Fq2) -> Fq2 {
-        let mut copy = *fe;
-        let t0 = copy.c0;
-        copy.c0 -= &fe.c1;
-        copy.c1 += &t0;
-        copy
+    fn mul_fp2_by_nonresidue_in_place(fe: &mut Fq2) -> &mut Fq2 {
+        let t0 = fe.c0;
+        fe.c0 -= &fe.c1;
+        fe.c1 += &t0;
+        fe
     }
 }

bls12_381/src/fields/tests.rs

@@ -1718,7 +1718,7 @@ fn test_fq2_legendre() {
     // i^2 = -1
     let mut m1 = -Fq2::one();
     assert_eq!(QuadraticResidue, m1.legendre());
-    m1 = Fq6Config::mul_fp2_by_nonresidue(&m1);
+    Fq6Config::mul_fp2_by_nonresidue_in_place(&mut m1);
     assert_eq!(QuadraticNonResidue, m1.legendre());
 }
 
@@ -1731,7 +1731,7 @@ fn test_fq2_mul_nonresidue() {
     for _ in 0..1000 {
         let mut a = Fq2::rand(&mut rng);
         let mut b = a;
-        a = Fq6Config::mul_fp2_by_nonresidue(&a);
+        Fq6Config::mul_fp2_by_nonresidue_in_place(&mut a);
         b.mul_assign(&nqr);
 
         assert_eq!(a, b);
@@ -1747,7 +1747,7 @@ fn test_fq6_mul_nonresidue() {
     for _ in 0..1000 {
         let mut a = Fq6::rand(&mut rng);
         let mut b = a;
-        a = Fq12Config::mul_fp6_by_nonresidue(&a);
+        Fq12Config::mul_fp6_by_nonresidue_in_place(&mut a);
         b.mul_assign(&nqr);
 
         assert_eq!(a, b);