primefield: update to safegcd-bounds (#1331)

Uses the new safegcd impl, which has a better strategy for computing the
upper bounds on the number of divstep operations.

It also has improved "bounds" in other ways, namely it's impl'd for all
sizes and no longer needs to rely on the `PrecomputedInverter` trait or
`SafeGcdInverter` type, even in `const fn` contexts.

Author: tarcieri

Cargo.lock

@@ -3,11 +3,9 @@
 
 use crate::ByteOrder;
 use bigint::{
-    ArrayEncoding, ByteArray, Integer, Invert, Odd, PrecomputeInverter, Uint,
+    ArrayEncoding, ByteArray, Integer, Invert, Uint,
     hybrid_array::{Array, ArraySize, typenum::Unsigned},
-    modular::{
-        ConstMontyForm as MontyForm, ConstMontyFormInverter, ConstMontyParams, SafeGcdInverter,
-    },
+    modular::{ConstMontyForm as MontyForm, ConstMontyFormInverter, ConstMontyParams},
 };
 use core::fmt::Formatter;
 use core::{
@@ -325,20 +323,14 @@ impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize> MontyFieldElement<MOD, LI
 
     /// Compute field inversion: `1 / self`.
     #[inline]
-    pub fn invert(&self) -> CtOption<Self>
-    where
-        MontyForm<MOD, LIMBS>: Invert<Output = CtOption<MontyForm<MOD, LIMBS>>>,
-    {
-        self.0.invert().map(Self)
+    pub fn invert(&self) -> CtOption<Self> {
+        CtOption::from(self.0.invert()).map(Self)
     }
 
     /// Compute field inversion as a `const fn`. Panics if `self` is zero.
     ///
     /// This is mainly intended for inverting constants at compile time.
-    pub const fn const_invert<const UNSAT_LIMBS: usize>(&self) -> Self
-    where
-        Odd<Uint<LIMBS>>: PrecomputeInverter<Inverter = SafeGcdInverter<LIMBS, UNSAT_LIMBS>, Output = Uint<LIMBS>>,
-    {
+    pub const fn const_invert(&self) -> Self {
         Self(
             ConstMontyFormInverter::<MOD, LIMBS>::new()
                 .invert(&self.0)
@@ -377,13 +369,10 @@ impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize> MontyFieldElement<MOD, LI
 // `ff` crate trait impls
 //
 
-impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize, const UNSAT_LIMBS: usize> Field
-    for MontyFieldElement<MOD, LIMBS>
+impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize> Field for MontyFieldElement<MOD, LIMBS>
 where
     Array<u8, MOD::ByteSize>: Copy,
     Uint<LIMBS>: ArrayEncoding,
-    Odd<Uint<LIMBS>>:
-        PrecomputeInverter<Inverter = SafeGcdInverter<LIMBS, UNSAT_LIMBS>, Output = Uint<LIMBS>>,
 {
     const ZERO: Self = Self::ZERO;
     const ONE: Self = Self::ONE;
@@ -424,13 +413,10 @@ where
     }
 }
 
-impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize, const UNSAT_LIMBS: usize> PrimeField
-    for MontyFieldElement<MOD, LIMBS>
+impl<MOD: MontyFieldParams<LIMBS>, const LIMBS: usize> PrimeField for MontyFieldElement<MOD, LIMBS>
 where
     Array<u8, MOD::ByteSize>: Copy,
     Uint<LIMBS>: ArrayEncoding,
-    Odd<Uint<LIMBS>>:
-        PrecomputeInverter<Inverter = SafeGcdInverter<LIMBS, UNSAT_LIMBS>, Output = Uint<LIMBS>>,
 {
     type Repr = Array<u8, MOD::ByteSize>;