A few more tests, ported (with some adaptations) from plonky1

src/field/field.rs

@@ -110,6 +110,21 @@ pub trait Field:
         subgroup
     }
 
+    fn cyclic_subgroup_unknown_order(generator: Self) -> Vec<Self> {
+        let mut subgroup = Vec::new();
+        for power in generator.powers() {
+            if power.is_one() && !subgroup.is_empty() {
+                break;
+            }
+            subgroup.push(power);
+        }
+        subgroup
+    }
+
+    fn generator_order(generator: Self) -> usize {
+        Self::cyclic_subgroup_unknown_order(generator).len()
+    }
+
     /// Computes a coset of a multiplicative subgroup whose order is known in advance.
     fn cyclic_subgroup_coset_known_order(generator: Self, shift: Self, order: usize) -> Vec<Self> {
         let subgroup = Self::cyclic_subgroup_known_order(generator, order);

src/field/field_testing.rs

@@ -225,35 +225,61 @@ macro_rules! test_arithmetic {
                 )
             }
 
-            // #[test]
-            // #[ignore]
-            // fn arithmetic_division() {
-            //     // This test takes ages to finish so is #[ignore]d by default.
-            //     // TODO: Re-enable and reimplement when
-            //     // https://github.com/rust-num/num-bigint/issues/60 is finally resolved.
-            //     let modulus = <$field>::ORDER;
-            //     crate::field::field_testing::run_binaryop_test_cases(
-            //         modulus,
-            //         WORD_BITS,
-            //         // Need to help the compiler infer the type of y here
-            //         |x: $field, y: $field| {
-            //             // TODO: Work out how to check that div() panics
-            //             // appropriately when given a zero divisor.
-            //             if !y.is_zero() {
-            //                 <$field>::div(x, y)
-            //             } else {
-            //                 <$field>::ZERO
-            //             }
-            //         },
-            //         |x, y| {
-            //             // yinv = y^-1 (mod modulus)
-            //             let exp = modulus - 2u64;
-            //             let yinv = y.modpow(exp, modulus);
-            //             // returns 0 if y was 0
-            //             x * yinv % modulus
-            //         },
-            //     )
-            // }
+            #[test]
+            fn inversion() {
+                let zero = <$field>::ZERO;
+                let one = <$field>::ONE;
+                let order = <$field>::ORDER;
+
+                assert_eq!(zero.try_inverse(), None);
+
+                for &x in &[1, 2, 3, order - 3, order - 2, order - 1] {
+                    let x = <$field>::from_canonical_u64(x);
+                    let inv = x.inverse();
+                    assert_eq!(x * inv, one);
+                }
+            }
+
+            #[test]
+            fn batch_inversion() {
+                let xs = (1..=3)
+                    .map(|i| <$field>::from_canonical_u64(i))
+                    .collect::<Vec<_>>();
+                let invs = <$field>::batch_multiplicative_inverse(&xs);
+                for (x, inv) in xs.into_iter().zip(invs) {
+                    assert_eq!(x * inv, <$field>::ONE);
+                }
+            }
+
+            #[test]
+            fn primitive_root_order() {
+                for n_power in 0..8 {
+                    let root = <$field>::primitive_root_of_unity(n_power);
+                    let order = <$field>::generator_order(root);
+                    assert_eq!(order, 1 << n_power, "2^{}'th primitive root", n_power);
+                }
+            }
+
+            #[test]
+            fn negation() {
+                let zero = <$field>::ZERO;
+                let order = <$field>::ORDER;
+
+                for &i in &[0, 1, 2, order - 2, order - 1] {
+                    let i_f = <$field>::from_canonical_u64(i);
+                    assert_eq!(i_f + -i_f, zero);
+                }
+            }
+
+            #[test]
+            fn bits() {
+                assert_eq!(<$field>::ZERO.bits(), 0);
+                assert_eq!(<$field>::ONE.bits(), 1);
+                assert_eq!(<$field>::TWO.bits(), 2);
+                assert_eq!(<$field>::from_canonical_u64(3).bits(), 2);
+                assert_eq!(<$field>::from_canonical_u64(4).bits(), 3);
+                assert_eq!(<$field>::from_canonical_u64(5).bits(), 3);
+            }
         }
     };
 }

src/polynomial/division.rs

@@ -60,8 +60,38 @@ pub(crate) fn divide_by_z_h<F: Field>(mut a: PolynomialCoeffs<F>, n: usize) -> P
 
 #[cfg(test)]
 mod tests {
+    use crate::field::crandall_field::CrandallField;
+    use crate::field::field::Field;
+    use crate::polynomial::division::divide_by_z_h;
+    use crate::polynomial::polynomial::PolynomialCoeffs;
+
+    #[test]
+    fn zero_div_z_h() {
+        type F = CrandallField;
+        let zero = PolynomialCoeffs::<F>::zero(16);
+        let quotient = divide_by_z_h(zero.clone(), 4);
+        assert_eq!(quotient, zero);
+    }
+
     #[test]
     fn division_by_z_h() {
-        // TODO
+        type F = CrandallField;
+        let zero = F::ZERO;
+        let one = F::ONE;
+        let two = F::TWO;
+        let three = F::from_canonical_u64(3);
+        let four = F::from_canonical_u64(4);
+        let five = F::from_canonical_u64(5);
+        let six = F::from_canonical_u64(6);
+
+        // a(x) = Z_4(x) q(x), where
+        // a(x) = 3 x^7 + 4 x^6 + 5 x^5 + 6 x^4 - 3 x^3 - 4 x^2 - 5 x - 6
+        // Z_4(x) = x^4 - 1
+        // q(x) = 3 x^3 + 4 x^2 + 5 x + 6
+        let a = PolynomialCoeffs::new(vec![-six, -five, -four, -three, six, five, four, three]);
+        let q = PolynomialCoeffs::new(vec![six, five, four, three, zero, zero, zero, zero]);
+
+        let computed_q = divide_by_z_h(a, 4);
+        assert_eq!(computed_q, q);
     }
 }

src/rescue.rs

@@ -502,6 +502,7 @@ fn sbox_layer_b<F: Field>(x: [F; W]) -> [F; W] {
 #[unroll_for_loops]
 fn sbox_a<F: Field>(x: F) -> F {
     // x^{-5}, via Fermat's little theorem
+    // TODO: This only works for our current field.
     const EXP: u64 = 7378697628517453005;
 
     let mut product = F::ONE;