Add SquareRoot trait (#508)

Author: fjarri

src/traits.rs

@@ -138,6 +138,7 @@ pub trait Integer:
     + for<'a> Sub<&'a Self, Output = Self>
     + SubMod<Output = Self>
     + Sync
+    + SquareRoot
     + WrappingAdd
     + WrappingSub
     + WrappingMul
@@ -463,6 +464,15 @@ pub trait SquareAssign {
     fn square_assign(&mut self);
 }
 
+/// Support for calucaling square roots.
+pub trait SquareRoot {
+    /// Computes `floor(sqrt(self))`.
+    fn sqrt(&self) -> Self;
+
+    /// Computes `floor(sqrt(self))`, variable time in `self`.
+    fn sqrt_vartime(&self) -> Self;
+}
+
 /// Support for optimized division by a single limb.
 pub trait DivRemLimb: Sized {
     /// Computes `self / rhs` using a pre-made reciprocal,

src/uint/boxed/sqrt.rs

@@ -2,7 +2,7 @@
 
 use subtle::{ConstantTimeEq, ConstantTimeGreater, CtOption};
 
-use crate::{BoxedUint, ConstantTimeSelect, NonZero};
+use crate::{BoxedUint, ConstantTimeSelect, NonZero, SquareRoot};
 
 impl BoxedUint {
     /// Computes √(`self`) in constant time.
@@ -121,6 +121,16 @@ impl BoxedUint {
     }
 }
 
+impl SquareRoot for BoxedUint {
+    fn sqrt(&self) -> Self {
+        self.sqrt()
+    }
+
+    fn sqrt_vartime(&self) -> Self {
+        self.sqrt_vartime()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{BoxedUint, Limb};

src/uint/sqrt.rs

@@ -1,6 +1,6 @@
 //! [`Uint`] square root operations.
 
-use crate::Uint;
+use crate::{SquareRoot, Uint};
 use subtle::{ConstantTimeEq, CtOption};
 
 impl<const LIMBS: usize> Uint<LIMBS> {
@@ -113,6 +113,16 @@ impl<const LIMBS: usize> Uint<LIMBS> {
     }
 }
 
+impl<const LIMBS: usize> SquareRoot for Uint<LIMBS> {
+    fn sqrt(&self) -> Self {
+        self.sqrt()
+    }
+
+    fn sqrt_vartime(&self) -> Self {
+        self.sqrt_vartime()
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{Limb, U192, U256};