move from rug to num-bigint (#53)

src/gadgets/utils.rs

@@ -10,7 +10,7 @@ use bellperson::{
 };
 use bellperson_nonnative::mp::bignat::{nat_to_limbs, BigNat};
 use ff::{Field, PrimeField, PrimeFieldBits};
-use rug::Integer;
+use num_bigint::BigInt;
 
 /// Gets as input the little indian representation of a number and spits out the number
 #[allow(dead_code)]
@@ -116,7 +116,7 @@ pub fn scalar_as_base<G: Group>(input: G::Scalar) -> G::Base {
 /// Allocate bignat a constant
 pub fn alloc_bignat_constant<F: PrimeField, CS: ConstraintSystem<F>>(
   mut cs: CS,
-  val: &Integer,
+  val: &BigInt,
   limb_width: usize,
   n_limbs: usize,
 ) -> Result<BigNat<F>, SynthesisError> {

src/pasta.rs

@@ -6,6 +6,8 @@ use crate::{
 use core::ops::Mul;
 use ff::Field;
 use merlin::Transcript;
+use num_bigint::BigInt;
+use num_traits::Num;
 use pasta_curves::{
   self,
   arithmetic::{CurveAffine, CurveExt, Group as Grp},
@@ -14,7 +16,6 @@ use pasta_curves::{
 };
 use rand::SeedableRng;
 use rand_chacha::ChaCha20Rng;
-use rug::Integer;
 
 //////////////////////////////////////Pallas///////////////////////////////////////////////
 
@@ -75,8 +76,8 @@ impl Group for pallas::Point {
     }
   }
 
-  fn get_order() -> Integer {
-    Integer::from_str_radix(
+  fn get_order() -> BigInt {
+    BigInt::from_str_radix(
       "40000000000000000000000000000000224698fc0994a8dd8c46eb2100000001",
       16,
     )
@@ -163,8 +164,8 @@ impl Group for vesta::Point {
     }
   }
 
-  fn get_order() -> Integer {
-    Integer::from_str_radix(
+  fn get_order() -> BigInt {
+    BigInt::from_str_radix(
       "40000000000000000000000000000000224698fc094cf91b992d30ed00000001",
       16,
     )

src/traits.rs

@@ -6,7 +6,7 @@ use core::{
 };
 use ff::{PrimeField, PrimeFieldBits};
 use merlin::Transcript;
-use rug::Integer;
+use num_bigint::BigInt;
 
 /// Represents an element of a group
 pub trait Group:
@@ -53,7 +53,7 @@ pub trait Group:
   fn to_coordinates(&self) -> (Self::Base, Self::Base, bool);
 
   /// Returns the order of the group as a big integer
-  fn get_order() -> Integer;
+  fn get_order() -> BigInt;
 }
 
 /// Represents a compressed version of a group element