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Implement linear combination addition with coefficient.

This commit is contained in:
Sean Bowe 2018-01-07 11:31:35 -07:00
parent dc981e6abc
commit 7211d98c1e
1 changed files with 52 additions and 8 deletions
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60
src/lib.rs
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@ -7,21 +7,22 @@ use std::error::Error;
/// This represents a linear combination of some variables, with coefficients
/// in the scalar field of a pairing-friendly elliptic curve group.
pub struct LinearCombination<T, E: Engine>(Vec<(T, E::Fr)>);
#[derive(Clone)]
pub struct LinearCombination<T: Copy, E: Engine>(Vec<(T, E::Fr)>);
impl<T, E: Engine> AsRef<[(T, E::Fr)]> for LinearCombination<T, E> {
impl<T: Copy, E: Engine> AsRef<[(T, E::Fr)]> for LinearCombination<T, E> {
fn as_ref(&self) -> &[(T, E::Fr)] {
&self.0
}
}
impl<T, E: Engine> LinearCombination<T, E> {
impl<T: Copy, E: Engine> LinearCombination<T, E> {
pub fn zero() -> LinearCombination<T, E> {
LinearCombination(vec![])
}
}
impl<T, E: Engine> Add<(E::Fr, T)> for LinearCombination<T, E> {
impl<T: Copy, E: Engine> Add<(E::Fr, T)> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn add(mut self, (coeff, var): (E::Fr, T)) -> LinearCombination<T, E> {
@ -31,7 +32,7 @@ impl<T, E: Engine> Add<(E::Fr, T)> for LinearCombination<T, E> {
}
}
impl<T, E: Engine> Sub<(E::Fr, T)> for LinearCombination<T, E> {
impl<T: Copy, E: Engine> Sub<(E::Fr, T)> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn sub(self, (mut coeff, var): (E::Fr, T)) -> LinearCombination<T, E> {
@ -41,7 +42,7 @@ impl<T, E: Engine> Sub<(E::Fr, T)> for LinearCombination<T, E> {
}
}
impl<T, E: Engine> Add<T> for LinearCombination<T, E> {
impl<T: Copy, E: Engine> Add<T> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn add(self, other: T) -> LinearCombination<T, E> {
@ -49,7 +50,7 @@ impl<T, E: Engine> Add<T> for LinearCombination<T, E> {
}
}
impl<T, E: Engine> Sub<T> for LinearCombination<T, E> {
impl<T: Copy, E: Engine> Sub<T> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn sub(self, other: T) -> LinearCombination<T, E> {
@ -81,9 +82,38 @@ impl<'a, T: Copy, E: Engine> Sub<&'a LinearCombination<T, E>> for LinearCombinat
}
}
impl<'a, T: Copy, E: Engine> Add<(E::Fr, &'a LinearCombination<T, E>)> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn add(mut self, (coeff, other): (E::Fr, &'a LinearCombination<T, E>)) -> LinearCombination<T, E> {
for s in &other.0 {
let mut tmp = s.1;
tmp.mul_assign(&coeff);
self = self + (tmp, s.0);
}
self
}
}
impl<'a, T: Copy, E: Engine> Sub<(E::Fr, &'a LinearCombination<T, E>)> for LinearCombination<T, E> {
type Output = LinearCombination<T, E>;
fn sub(mut self, (coeff, other): (E::Fr, &'a LinearCombination<T, E>)) -> LinearCombination<T, E> {
for s in &other.0 {
let mut tmp = s.1;
tmp.mul_assign(&coeff);
self = self - (tmp, s.0);
}
self
}
}
#[test]
fn test_lc() {
use pairing::bls12_381::{Bls12, Fr};
use pairing::PrimeField;
let a = LinearCombination::<usize, Bls12>::zero() + 0usize + 1usize + 2usize - 3usize;
@ -94,7 +124,7 @@ fn test_lc() {
let x = LinearCombination::<usize, Bls12>::zero() + (Fr::one(), 0usize) - (Fr::one(), 1usize);
let y = LinearCombination::<usize, Bls12>::zero() + (Fr::one(), 2usize) - (Fr::one(), 3usize);
let z = x + &y - &y;
let z = x.clone() + &y - &y;
assert_eq!(z.0, vec![
(0usize, Fr::one()),
@ -104,6 +134,20 @@ fn test_lc() {
(2usize, negone),
(3usize, Fr::one())
]);
let coeff = Fr::from_str("3").unwrap();
let mut neg_coeff = coeff;
neg_coeff.negate();
let z = x + (coeff, &y) - (coeff, &y);
assert_eq!(z.0, vec![
(0usize, Fr::one()),
(1usize, negone),
(2usize, Fr::from_str("3").unwrap()),
(3usize, neg_coeff),
(2usize, neg_coeff),
(3usize, Fr::from_str("3").unwrap())
]);
}
/// This is an error that could occur during circuit synthesis contexts,