diff --git a/src/edwards.rs b/src/edwards.rs index 8487073..5ba490c 100644 --- a/src/edwards.rs +++ b/src/edwards.rs @@ -98,6 +98,7 @@ use core::iter::Iterator; use core::ops::{Add, Sub, Neg}; use core::ops::{AddAssign, SubAssign}; use core::ops::{Mul, MulAssign}; +use core::iter::Sum; use core::borrow::Borrow; use subtle::ConditionallyAssignable; @@ -427,6 +428,19 @@ impl<'b> SubAssign<&'b EdwardsPoint> for EdwardsPoint { define_sub_assign_variants!(LHS = EdwardsPoint, RHS = EdwardsPoint); +impl Sum for EdwardsPoint +where + T: Borrow +{ + fn sum(iter: I) -> Self + where + I: Iterator + { + iter.fold(EdwardsPoint::identity(), |acc, item| acc + item.borrow()) + } +} + + // ------------------------------------------------------------------------ // Negation // ------------------------------------------------------------------------ @@ -1092,6 +1106,38 @@ mod test { assert_eq!(bp16.compress(), BASE16_CMPRSSD); } + #[test] + fn impl_sum() { + + // Test that sum works for non-empty iterators + let BASE = constants::ED25519_BASEPOINT_POINT; + + let s1 = Scalar::from_u64(999); + let P1 = &BASE * &s1; + + let s2 = Scalar::from_u64(333); + let P2 = &BASE * &s2; + + let vec = vec![P1.clone(), P2.clone()]; + let sum: EdwardsPoint = vec.iter().sum(); + + assert_eq!(sum, P1 + P2); + + // Test that sum works for the empty iterator + let empty_vector: Vec = vec![]; + let sum: EdwardsPoint = empty_vector.iter().sum(); + + assert_eq!(sum, EdwardsPoint::identity()); + + // Test that sum works on owning iterators + let s = Scalar::from_u64(2); + let mapped = vec.iter().map(|x| x * &s); + let sum: EdwardsPoint = mapped.sum(); + + assert_eq!(sum, &P1 * &s + &P2 * &s); + } + + /// Test that the conditional assignment trait works for AffineNielsPoints. #[test] fn conditional_assign_for_affine_niels_point() {