Use ConstZero trait from num_traits (#573)

Added in rust-num/num-traits#303

Cargo.toml

@@ -22,7 +22,7 @@ subtle = { version = "2.5", default-features = false }
 # optional dependencies
 der = { version = "0.7", optional = true, default-features = false }
 hybrid-array = { version = "0.2.0-rc.4", optional = true }
-num-traits = { version = "0.2", default-features = false }
+num-traits = { version = "0.2.18", default-features = false }
 rand_core = { version = "0.6.4", optional = true }
 rlp = { version = "0.5", optional = true, default-features = false }
 serdect = { version = "0.2", optional = true, default-features = false }

src/modular/const_monty_form.rs

@@ -185,6 +185,18 @@ impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> ConstZero for ConstMontyF
     const ZERO: Self = Self::ZERO;
 }
 
+impl<MOD: ConstMontyParams<LIMBS>, const LIMBS: usize> num_traits::Zero
+    for ConstMontyForm<MOD, LIMBS>
+{
+    fn zero() -> Self {
+        Self::ZERO
+    }
+
+    fn is_zero(&self) -> bool {
+        self.ct_eq(&Self::ZERO).into()
+    }
+}
+
 #[cfg(feature = "rand_core")]
 impl<MOD, const LIMBS: usize> Random for ConstMontyForm<MOD, LIMBS>
 where

src/traits.rs

@@ -3,7 +3,7 @@
 mod sealed;
 
 pub use num_traits::{
-    WrappingAdd, WrappingMul, WrappingNeg, WrappingShl, WrappingShr, WrappingSub,
+    ConstZero, WrappingAdd, WrappingMul, WrappingNeg, WrappingShl, WrappingShr, WrappingSub,
 };
 
 pub(crate) use sealed::PrecomputeInverterWithAdjuster;
@@ -264,15 +264,7 @@ pub trait Zero: ConstantTimeEq + Sized {
     }
 }
 
-/// Trait for associating a constant representing zero.
-///
-/// Types which impl this trait automatically receive a blanket impl of [`Zero`].
-pub trait ConstZero: Zero {
-    /// The value `0`.
-    const ZERO: Self;
-}
-
-impl<T: ConstZero> Zero for T {
+impl<T: ConstZero + ConstantTimeEq> Zero for T {
     #[inline(always)]
     fn zero() -> T {
         Self::ZERO