group: Sum + for<'a> Sum<&'a Self> bounds for Group

bellman/src/groth16/tests/dummy_engine.rs

@@ -4,6 +4,7 @@ use pairing::{Engine, PairingCurveAffine};
 
 use rand_core::RngCore;
 use std::fmt;
+use std::iter::Sum;
 use std::num::Wrapping;
 use std::ops::{Add, AddAssign, BitAnd, Mul, MulAssign, Neg, Shr, Sub, SubAssign};
 use subtle::{Choice, ConditionallySelectable, ConstantTimeEq, CtOption};
@@ -47,6 +48,18 @@ impl ConditionallySelectable for Fr {
     }
 }
 
+impl Sum for Fr {
+    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
+        iter.fold(Self::zero(), ::std::ops::Add::add)
+    }
+}
+
+impl<'r> Sum<&'r Fr> for Fr {
+    fn sum<I: Iterator<Item = &'r Fr>>(iter: I) -> Self {
+        iter.fold(Self::zero(), ::std::ops::Add::add)
+    }
+}
+
 impl Neg for Fr {
     type Output = Self;
 

group/src/lib.rs

@@ -5,6 +5,7 @@ use ff::{Field, PrimeField};
 use rand::RngCore;
 use std::error::Error;
 use std::fmt;
+use std::iter::Sum;
 use std::ops::{Add, AddAssign, Neg, Sub, SubAssign};
 
 pub mod tests;
@@ -38,6 +39,8 @@ pub trait Group:
     + Send
     + Sync
     + 'static
+    + Sum
+    + for<'a> Sum<&'a Self>
     + Neg<Output = Self>
     + GroupOps
     + GroupOpsOwned

pairing/src/bls12_381/ec.rs

@@ -205,6 +205,18 @@ macro_rules! curve_impl {
             }
         }
 
+        impl ::std::iter::Sum for $projective {
+            fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
+                iter.fold(Self::identity(), ::std::ops::Add::add)
+            }
+        }
+
+        impl<'r> ::std::iter::Sum<&'r $projective> for $projective {
+            fn sum<I: Iterator<Item = &'r $projective>>(iter: I) -> Self {
+                iter.fold(Self::identity(), ::std::ops::Add::add)
+            }
+        }
+
         impl ::std::ops::Neg for $projective {
             type Output = Self;