apply suggestions

calculate extension field zeta in compile time

bring back some removed comments

derive/src/field/arith.rs

@@ -177,6 +177,8 @@ fn impl_add(field: &syn::Ident, num_limbs: usize) -> TokenStream {
         gen.extend(quote! { let ( #d_i, carry) = adc(self.0[#i], rhs.0[#i], #carry); });
     });
 
+    // Attempt to subtract the modulus, to ensure the value
+    // is smaller than the modulus.
     (0..num_limbs).for_each(|i| {
         let borrow = select(i == 0, quote! {0}, quote! {borrow});
         let d_i = fmtid!("d_{}", i);

src/bn256/fq2.rs

@@ -178,13 +178,6 @@ impl FromUniformBytes<96> for Fq2 {
     }
 }
 
-const ZETA: Fq = Fq::from_raw([
-    0x5763473177fffffe,
-    0xd4f263f1acdb5c4f,
-    0x59e26bcea0d48bac,
-    0x0000000000000000,
-]);
-
 #[cfg(test)]
 mod test {
     use super::*;

src/derive/field/tower.rs

@@ -268,7 +268,7 @@ macro_rules! impl_tower2 {
         impl WithSmallOrderMulGroup<3> for $tower {
             // $field::ZETA ^2
             const ZETA: Self = $tower {
-                c0: ZETA,
+                c0: $field::ZETA.mul_const(&$field::ZETA),
                 c1: $field::ZERO,
             };
         }

src/pluto_eris/fp12.rs

@@ -187,10 +187,16 @@ impl Field for Fp12 {
     }
 
     fn sqrt(&self) -> CtOption<Self> {
+        // The square root method is typically only required for finding y-coordinate
+        // given the x-coordinate of an EC point. Fields over which we have not
+        // defined a curve do not need this method.
         unimplemented!()
     }
 
     fn sqrt_ratio(_num: &Self, _div: &Self) -> (Choice, Self) {
+        // The square root method is typically only required for finding y-coordinate
+        // given the x-coordinate of an EC point. Fields over which we have not
+        // defined a curve do not need this method.
         unimplemented!()
     }
 

src/pluto_eris/fp2.rs

@@ -185,16 +185,6 @@ impl Fp2 {
     }
 }
 
-const ZETA: Fp = Fp::from_raw([
-    0x8ffff80f80000002,
-    0xd9fa5d8a200bc439,
-    0x1b50d5e1ff708dc8,
-    0xf43f8cddf9a5c478,
-    0xa803ca76be3924a5,
-    0x0130e0000d7f28e4,
-    0x2400000000002400,
-]);
-
 #[cfg(test)]
 mod test {
     use super::*;