Make Field::square take &self and return Self

zcash_primitives/src/jubjub/fs.rs

@@ -575,7 +575,7 @@ impl Field for Fs {
     }
 
     #[inline]
-    fn square(&mut self) {
+    fn square(&self) -> Self {
         let mut carry = 0;
         let r1 = mac_with_carry(0, (self.0).0[0], (self.0).0[1], &mut carry);
         let r2 = mac_with_carry(0, (self.0).0[0], (self.0).0[2], &mut carry);
@@ -606,7 +606,10 @@ impl Field for Fs {
         let r5 = adc(r5, 0, &mut carry);
         let r6 = mac_with_carry(r6, (self.0).0[3], (self.0).0[3], &mut carry);
         let r7 = adc(r7, 0, &mut carry);
-        self.mont_reduce(r0, r1, r2, r3, r4, r5, r6, r7);
+
+        let mut ret = *self;
+        ret.mont_reduce(r0, r1, r2, r3, r4, r5, r6, r7);
+        ret
     }
 }
 
@@ -736,8 +739,7 @@ impl SqrtField for Fs {
             0x4199cec0404d0ec0,
             0x39f6d3a994cebea,
         ]);
-        let mut a0 = a1;
-        a0.square();
+        let mut a0 = a1.square();
         a0.mul_assign(self);
 
         if a0 == NEGATIVE_ONE {
@@ -1403,16 +1405,15 @@ fn test_fs_mul_assign() {
 
 #[test]
 fn test_fr_squaring() {
-    let mut a = Fs(FsRepr([
+    let a = Fs(FsRepr([
         0xffffffffffffffff,
         0xffffffffffffffff,
         0xffffffffffffffff,
         0xe7db4ea6533afa8,
     ]));
     assert!(a.is_valid());
-    a.square();
     assert_eq!(
-        a,
+        a.square(),
         Fs::from_repr(FsRepr([
             0x12c7f55cbc52fbaa,
             0xdedc98a0b5e6ce9e,
@@ -1431,8 +1432,7 @@ fn test_fr_squaring() {
         // Ensure that (a * a) = a^2
         let a = Fs::random(&mut rng);
 
-        let mut tmp = a;
-        tmp.square();
+        let tmp = a.square();
 
         let mut tmp2 = a;
         tmp2.mul_assign(&a);
@@ -1538,8 +1538,7 @@ fn test_fs_sqrt() {
         // Ensure sqrt(a^2) = a or -a
         let a = Fs::random(&mut rng);
         let nega = a.neg();
-        let mut b = a;
-        b.square();
+        let b = a.square();
 
         let b = b.sqrt().unwrap();
 
@@ -1550,10 +1549,8 @@ fn test_fs_sqrt() {
         // Ensure sqrt(a)^2 = a for random a
         let a = Fs::random(&mut rng);
 
-        if let Some(mut tmp) = a.sqrt() {
-            tmp.square();
-
-            assert_eq!(a, tmp);
+        if let Some(tmp) = a.sqrt() {
+            assert_eq!(a, tmp.square());
         }
     }
 }