From facbe117fbd966c17ed7fdddc0086d8ae81bd990 Mon Sep 17 00:00:00 2001
From: Daniel Lubarov <daniel@lubarov.com>
Date: Fri, 2 Apr 2021 19:04:26 -0700
Subject: [PATCH] Move some stuff into Field

---
 src/field/crandall_field.rs | 24 ++++--------------------
 src/field/field.rs          | 23 ++++++++++++++++++++---
 src/field/field_testing.rs  |  2 +-
 src/polynomial/division.rs  |  2 +-
 4 files changed, 26 insertions(+), 25 deletions(-)

diff --git a/src/field/crandall_field.rs b/src/field/crandall_field.rs
index 8b9dc9e3..4fc839bf 100644
--- a/src/field/crandall_field.rs
+++ b/src/field/crandall_field.rs
@@ -9,9 +9,6 @@ use crate::field::field::Field;
 /// EPSILON = 9 * 2**28 - 1
 const EPSILON: u64 = 2415919103;
 
-const TWO_ADICITY: usize = 28;
-const POWER_OF_TWO_GENERATOR: CrandallField = CrandallField(10281950781551402419);
-
 /// A field designed for use with the Crandall reduction algorithm.
 ///
 /// Its order is
@@ -51,7 +48,10 @@ impl Field for CrandallField {
     const NEG_ONE: Self = Self(Self::ORDER - 1);
 
     const ORDER: u64 = 18446744071293632513;
-    const MULTIPLICATIVE_SUBGROUP_GENERATOR: Self = Self(5);
+    const TWO_ADICITY: usize = 28;
+
+    const MULTIPLICATIVE_GROUP_GENERATOR: Self = Self(5);
+    const POWER_OF_TWO_GENERATOR: Self = Self(10281950781551402419);
 
     #[inline]
     fn square(&self) -> Self {
@@ -119,22 +119,6 @@ impl Field for CrandallField {
         }))
     }
 
-    fn primitive_root_of_unity(n_power: usize) -> Self {
-        assert!(n_power <= TWO_ADICITY);
-        let base = POWER_OF_TWO_GENERATOR;
-        base.exp(CrandallField(1u64 << (TWO_ADICITY - n_power)))
-    }
-
-    fn cyclic_subgroup_known_order(generator: Self, order: usize) -> Vec<Self> {
-        let mut subgroup = Vec::new();
-        let mut current = Self::ONE;
-        for _i in 0..order {
-            subgroup.push(current);
-            current = current * generator;
-        }
-        subgroup
-    }
-
     #[inline]
     fn to_canonical_u64(&self) -> u64 {
         let mut c = self.0;
diff --git a/src/field/field.rs b/src/field/field.rs
index 239b0160..7cffab50 100644
--- a/src/field/field.rs
+++ b/src/field/field.rs
@@ -27,7 +27,12 @@ pub trait Field: 'static
     const NEG_ONE: Self;
 
     const ORDER: u64;
-    const MULTIPLICATIVE_SUBGROUP_GENERATOR: Self;
+    const TWO_ADICITY: usize;
+
+    /// Generator of the entire multiplicative group, i.e. all non-zero elements.
+    const MULTIPLICATIVE_GROUP_GENERATOR: Self;
+    /// Generator of a multiplicative subgroup of order `2^TWO_ADICITY`.
+    const POWER_OF_TWO_GENERATOR: Self;
 
     fn is_zero(&self) -> bool {
         *self == Self::ZERO
@@ -81,9 +86,21 @@ pub trait Field: 'static
         x_inv
     }
 
-    fn primitive_root_of_unity(n_power: usize) -> Self;
+    fn primitive_root_of_unity(n_power: usize) -> Self {
+        assert!(n_power <= Self::TWO_ADICITY);
+        let base = Self::POWER_OF_TWO_GENERATOR;
+        base.exp(Self::from_canonical_u64(1u64 << (Self::TWO_ADICITY - n_power)))
+    }
 
-    fn cyclic_subgroup_known_order(generator: Self, order: usize) -> Vec<Self>;
+    fn cyclic_subgroup_known_order(generator: Self, order: usize) -> Vec<Self> {
+        let mut subgroup = Vec::new();
+        let mut current = Self::ONE;
+        for _i in 0..order {
+            subgroup.push(current);
+            current = current * generator;
+        }
+        subgroup
+    }
 
     fn to_canonical_u64(&self) -> u64;
 
diff --git a/src/field/field_testing.rs b/src/field/field_testing.rs
index c5a7d259..ca42a4c2 100644
--- a/src/field/field_testing.rs
+++ b/src/field/field_testing.rs
@@ -137,7 +137,7 @@ macro_rules! test_arithmetic {
     ($field:ty) => {
         mod arithmetic {
             use crate::{Field};
-            use std::ops::{Add, Div, Mul, Neg, Sub};
+            use std::ops::{Add, Mul, Neg, Sub};
 
             // Can be 32 or 64; doesn't have to be computer's actual word
             // bits. Choosing 32 gives more tests...
diff --git a/src/polynomial/division.rs b/src/polynomial/division.rs
index 68c78612..9ee72d04 100644
--- a/src/polynomial/division.rs
+++ b/src/polynomial/division.rs
@@ -12,7 +12,7 @@ pub(crate) fn divide_by_z_h<F: Field>(mut a: PolynomialCoeffs<F>, n: usize) -> P
         return a.clone();
     }
 
-    let g = F::MULTIPLICATIVE_SUBGROUP_GENERATOR;
+    let g = F::MULTIPLICATIVE_GROUP_GENERATOR;
     let mut g_pow = F::ONE;
     // Multiply the i-th coefficient of `a` by `g^i`. Then `new_a(w^j) = old_a(g.w^j)`.
     a.coeffs.iter_mut().for_each(|x| {