programming-bitcoin/src/ecc.rs at main · smirror/programming-bitcoin · GitHub

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use crate::lib::pow_mod;

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct FieldElement {
    num: i64,
    prime: i64,
}

impl FieldElement {
    pub fn init(num: i64, prime: i64) -> FieldElement {
        // if num >= prime {
        //     panic!("num {} not in field range 0 to {}", num, prime - 1);
        // }
        FieldElement {
            num: num % prime,
            prime,
        }
    }

    pub fn add(&self, other: &FieldElement) -> FieldElement {
        if &self.prime != &other.prime {
            panic!("cannot add elements from different prime fields");
        }
        FieldElement::init(self.num + other.num, self.prime)
    }

    pub fn sub(&self, other: &FieldElement) -> FieldElement {
        if &self.prime != &other.prime {
            panic!("cannot subtract elements from different prime fields");
        }
        FieldElement::init(self.num - other.num, self.prime)
    }

    pub fn mul(&self, other: &FieldElement) -> FieldElement {
        if &self.prime != &other.prime {
            panic!("cannot multiply elements from different prime fields");
        }
        FieldElement::init(self.num * other.num, self.prime)
    }

    pub fn pow(&self, exp: i64) -> FieldElement {
        FieldElement::init(pow_mod(self.num, exp, self.prime as i32), self.prime)
    }
}

#[cfg(test)]
mod tests {
    use crate::ecc::FieldElement;

    #[test]
    fn test_partial_eq() {
        let a = FieldElement::init(7, 13);
        let b = FieldElement::init(6, 13);
        assert_eq!(a == b, false);
        assert_eq!(a != b, true);
    }

    #[test]
    fn ex1_1() {
        let a = FieldElement::init(7, 13);
        let b = FieldElement::init(6, 13);
        assert_eq!(a != b, true);
    }

    #[test]
    fn test_eq() {
        let a = FieldElement::init(7, 13);
        let b = FieldElement::init(6, 13);
        assert_eq!(a == a, true);
    }

    #[test]
    fn ex1_2_1() {
        let a = FieldElement::init(44, 57);
        let b = FieldElement::init(33, 57);
        let c = FieldElement::init(77, 57);
        assert_eq!(a.add(&b), c);
    }

    #[test]
    fn ex1_2_2() {
        let a = FieldElement::init(9, 57);
        let b = FieldElement::init(29, 57);
        let c = FieldElement::init(-20, 57);
        assert_eq!(a.sub(&b), c);
    }

    #[test]
    fn ex1_2_3() {
        let a = FieldElement::init(17, 57);
        let b = FieldElement::init(42, 57);
        let c = FieldElement::init(49, 57);
        let d = FieldElement::init(108, 57);
        assert_eq!(a.add(&b).add(&c), d);
    }

    #[test]
    fn ex1_2_4() {
        let a = FieldElement::init(52, 57);
        let b = FieldElement::init(30, 57);
        let c = FieldElement::init(38, 57);
        let d = FieldElement::init(-16, 57);
        assert_eq!(a.sub(&b).sub(&c), d);
    }

    #[test]
    fn ex1_3_1() {
        let a = FieldElement::init(95, 97);
        let b = FieldElement::init(45, 97);
        let c = FieldElement::init(31, 97);
        let d = FieldElement::init(95 * 45 * 31, 97);
        assert_eq!(a.mul(&b).mul(&c), d);
    }

    #[test]
    fn ex1_3_2() {
        let a = FieldElement::init(17, 97);
        let b = FieldElement::init(13, 97);
        let c = FieldElement::init(19, 97);
        let d = FieldElement::init(44, 97);
        assert_eq!(
            a.mul(&b).mul(&c).mul(&d),
            FieldElement::init(17 * 13 * 19 * 44, 97)
        );
    }

    #[test]
    fn ex1_3_3() {
        let a = FieldElement::init(12, 97);
        let b = FieldElement::init(77, 97);
        let c = FieldElement::init(8 * 20, 97);
        assert_eq!(a.pow(7).mul(&b.pow(49)), c);
    }
}