PrimeFieldRepr::divn() should accept u32.

src/bls12_381/fq.rs

@@ -10,7 +10,7 @@ const MODULUS_BITS: u32 = 381;
 
 // The number of bits that must be shaved from the beginning of
 // the representation when randomly sampling.
-const REPR_SHAVE_BITS: usize = 3;
+const REPR_SHAVE_BITS: u32 = 3;
 
 // R = 2**384 % q
 const R: FqRepr = FqRepr([0x760900000002fffd, 0xebf4000bc40c0002, 0x5f48985753c758ba, 0x77ce585370525745, 0x5c071a97a256ec6d, 0x15f65ec3fa80e493]);
@@ -278,7 +278,7 @@ impl PrimeFieldRepr for FqRepr {
     }
 
     #[inline(always)]
-    fn divn(&mut self, mut n: usize) {
+    fn divn(&mut self, mut n: u32) {
         if n >= 64 * 6 {
             *self = Self::from(0);
             return;

src/bls12_381/fr.rs

@@ -8,7 +8,7 @@ const MODULUS_BITS: u32 = 255;
 
 // The number of bits that must be shaved from the beginning of
 // the representation when randomly sampling.
-const REPR_SHAVE_BITS: usize = 1;
+const REPR_SHAVE_BITS: u32 = 1;
 
 // R = 2**256 % r
 const R: FrRepr = FrRepr([0x1fffffffe, 0x5884b7fa00034802, 0x998c4fefecbc4ff5, 0x1824b159acc5056f]);
@@ -114,7 +114,7 @@ impl PrimeFieldRepr for FrRepr {
     }
 
     #[inline(always)]
-    fn divn(&mut self, mut n: usize) {
+    fn divn(&mut self, mut n: u32) {
         if n >= 64 * 4 {
             *self = Self::from(0);
             return;

src/lib.rs

@@ -369,7 +369,7 @@ pub trait PrimeFieldRepr: Sized +
     fn div2(&mut self);
 
     /// Performs a rightwise bitshift of this number by some amount.
-    fn divn(&mut self, amt: usize);
+    fn divn(&mut self, amt: u32);
 
     /// Performs a leftwise bitshift of this number, effectively multiplying
     /// it by 2. Overflow is ignored.