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Implement addition and multiplication operations for AffinePoint #112

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Implement addition and multiplication operations for AffinePoint #112

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b17735b
Implement addition and multiplication operations for AffinePoint
FilipLaurentiu Jan 22, 2025
bda4849
Simplify the `mul` function.
FilipLaurentiu Jan 22, 2025
3018ffc
Add missing documentation for `generator` and `mul` function
FilipLaurentiu Jan 23, 2025
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81 changes: 75 additions & 6 deletions crates/starknet-types-core/src/curve/affine_point.rs
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Original file line number Diff line number Diff line change
@@ -1,9 +1,13 @@
use crate::curve::curve_errors::CurveError;
use crate::felt::Felt;
use lambdaworks_math::cyclic_group::IsGroup;
use lambdaworks_math::elliptic_curve::short_weierstrass::curves::stark_curve::StarkCurve;
use lambdaworks_math::elliptic_curve::short_weierstrass::point::ShortWeierstrassProjectivePoint;
use lambdaworks_math::elliptic_curve::traits::FromAffine;
use crate::{curve::curve_errors::CurveError, felt::Felt};
use lambdaworks_math::{
cyclic_group::IsGroup,
elliptic_curve::{
short_weierstrass::{
curves::stark_curve::StarkCurve, point::ShortWeierstrassProjectivePoint,
},
traits::{FromAffine, IsEllipticCurve},
},
};

/// Represents a point on the Stark elliptic curve.
/// Doc: https://docs.starkware.co/starkex/crypto/stark-curve.html
Expand Down Expand Up @@ -47,6 +51,15 @@ impl AffinePoint {
pub fn y(&self) -> Felt {
Felt(*self.0.y())
}

pub fn generator() -> Self {
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AffinePoint(StarkCurve::generator())
}

pub fn mul(&self, exponent: Felt) -> Self {
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let exponent = exponent.representative();
AffinePoint(self.0.operate_with_self(exponent))
}
}

impl core::ops::Neg for &AffinePoint {
Expand All @@ -57,6 +70,14 @@ impl core::ops::Neg for &AffinePoint {
}
}

impl core::ops::Add for &AffinePoint {
type Output = AffinePoint;

fn add(self, rhs: Self) -> Self::Output {
AffinePoint(self.0.operate_with_affine(&rhs.0))
}
}

#[cfg(test)]
mod test {
use super::*;
Expand Down Expand Up @@ -117,4 +138,52 @@ mod test {
);
assert_eq!(-&AffinePoint::identity(), AffinePoint::identity());
}

#[test]
fn affine_add() {
let p = AffinePoint::new(
Felt::from_hex_unchecked("0x2d39148a92f479fb077389d"),
Felt::from_hex_unchecked(
"0x6e5d97edf7283fe7a7fe9deef2619224f42cb1bd531dd23380ad066c61ee20b",
),
)
.unwrap();

assert_eq!(
&p + &p,
AffinePoint::new(
Felt::from_hex_unchecked(
"0x23a1c9a32dd397fb1e7f758b9089757c1223057aea1d8b52cbec583ad74eaab",
),
Felt::from_hex_unchecked(
"0x466880caf4086bac129ae52ee98ddf75b2b394ae7c7ed1a19d9c61aa1f69f62",
),
)
.unwrap()
);
}

#[test]
fn affine_mul() {
let p = AffinePoint::new(
Felt::from_hex_unchecked("0x2d39148a92f479fb077389d"),
Felt::from_hex_unchecked(
"0x6e5d97edf7283fe7a7fe9deef2619224f42cb1bd531dd23380ad066c61ee20b",
),
)
.unwrap();

assert_eq!(
p.mul(Felt::from(2)),
AffinePoint::new(
Felt::from_hex_unchecked(
"0x23a1c9a32dd397fb1e7f758b9089757c1223057aea1d8b52cbec583ad74eaab",
),
Felt::from_hex_unchecked(
"0x466880caf4086bac129ae52ee98ddf75b2b394ae7c7ed1a19d9c61aa1f69f62",
),
)
.unwrap()
);
}
}
14 changes: 9 additions & 5 deletions crates/starknet-types-core/src/felt/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -295,7 +295,7 @@ impl Felt {

/// Quotient and remainder between `self` and `rhs`.
pub fn div_rem(&self, rhs: &NonZeroFelt) -> (Self, Self) {
let (q, r) = self.0.representative().div_rem(&rhs.0.representative());
let (q, r) = self.representative().div_rem(&rhs.0.representative());
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doesn't this change the behaviour?

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the self.representative() function returns self.0.representative() so it's the same.
I had to add the public function representative to get the representation of a Felt for the operate_with_self function in order to multiply the point with itself.
Adding representative() function to Felt and replace the old way of using it make the code cleaner.

(Self(FieldElement::from(&q)), Self(FieldElement::from(&r)))
}

Expand Down Expand Up @@ -412,20 +412,24 @@ impl Felt {
/// Convert `self`'s representative into an array of `u64` digits,
/// least significant digits first.
pub fn to_le_digits(&self) -> [u64; 4] {
let mut limbs = self.0.representative().limbs;
let mut limbs = self.representative().limbs;
limbs.reverse();
limbs
}

pub fn representative(&self) -> UnsignedInteger<4> {
self.0.representative()
}

/// Convert `self`'s representative into an array of `u64` digits,
/// most significant digits first.
pub fn to_be_digits(&self) -> [u64; 4] {
self.0.representative().limbs
self.representative().limbs
}

/// Count the minimum number of bits needed to express `self`'s representative.
pub fn bits(&self) -> usize {
self.0.representative().bits_le()
self.representative().bits_le()
}

pub fn to_biguint(&self) -> BigUint {
Expand Down Expand Up @@ -961,7 +965,7 @@ mod formatting {

let mut buf = [0u8; 4 * 20];
let mut i = buf.len() - 1;
let mut current = self.0.representative();
let mut current = self.representative();
let ten = UnsignedInteger::from(10_u16);

loop {
Expand Down