Merge pull request #5835 from oasisprotocol/peternose/trivial/fix-set…

…-coefficient

secret-sharing/src/poly: Return bool when setting coefficient

secret-sharing/src/churp/dealer.rs

@@ -41,7 +41,8 @@ where
     /// Creates a new dealer with a predefined shared secret.
     pub fn new(threshold: u8, secret: G::Scalar, rng: &mut impl RngCore) -> Result<Self> {
         let mut bp = Self::random_bivariate_polynomial(threshold, rng)?;
-        bp.set_coefficient(0, 0, secret);
+        let updated = bp.set_coefficient(0, 0, secret);
+        debug_assert!(updated);
         Ok(bp.into())
     }
 

secret-sharing/src/poly/bivariate.rs

@@ -82,18 +82,21 @@ where
     /// Sets the coefficient `b_{i,j}` that belongs to the term `x^i y^j`.
     ///
     /// If the coefficient does not exist, this is a no-op.
-    pub fn set_coefficient(&mut self, i: usize, j: usize, bij: F) {
+    pub fn set_coefficient(&mut self, i: usize, j: usize, bij: F) -> bool {
         if let Some(bi) = self.b.get_mut(i) {
             if let Some(old_bij) = bi.get_mut(j) {
                 *old_bij = bij;
+                return true;
             }
         }
+        false
     }
 
     /// Sets the coefficient `b_{0,0}` of the constant term to zero,
     /// effectively creating a zero-hole bivariate polynomial.
     pub fn to_zero_hole(&mut self) {
-        self.set_coefficient(0, 0, F::ZERO);
+        let updated = self.set_coefficient(0, 0, F::ZERO);
+        debug_assert!(updated);
     }
 
     /// Returns true iff the coefficient `b_{0,0}` of the constant term is zero.
@@ -338,7 +341,7 @@ mod tests {
         let mut bp = BivariatePolynomial::zero(2, 3);
         assert_eq!(bp.b[0][0], scalar(0));
 
-        bp.set_coefficient(0, 0, scalar(1));
+        assert!(bp.set_coefficient(0, 0, scalar(1)));
         assert_eq!(bp.b[0][0], scalar(1));
     }
 
@@ -347,7 +350,7 @@ mod tests {
         let mut rng: StdRng = SeedableRng::from_seed([1u8; 32]);
         let mut bp = BivariatePolynomial::random(2, 3, &mut rng);
 
-        bp.set_coefficient(0, 0, scalar(1));
+        assert!(bp.set_coefficient(0, 0, scalar(1)));
         assert_eq!(bp.b[0][0], scalar(1));
 
         bp.to_zero_hole();

secret-sharing/src/poly/univariate.rs

@@ -21,8 +21,7 @@ use crate::poly::powers;
 ///
 /// Trailing zeros are never trimmed to ensure that all polynomials of the same
 /// degree are consistently represented by vectors of the same size, resulting
-/// in encodings of equal length. If you wish to remove them, consider using
-/// the `trim` method after each operation.
+/// in encodings of equal length.
 #[derive(Clone, PartialEq, Eq)]
 pub struct Polynomial<F> {
     pub(crate) a: Vec<F>,
@@ -68,16 +67,19 @@ where
     /// Sets the coefficient `a_i` that belongs to the term `x^i`.
     ///
     /// If the coefficient does not exist, this is a no-op.
-    pub fn set_coefficient(&mut self, i: usize, ai: F) {
+    pub fn set_coefficient(&mut self, i: usize, ai: F) -> bool {
         if let Some(old_ai) = self.a.get_mut(i) {
             *old_ai = ai;
+            return true;
         }
+        false
     }
 
     /// Sets the coefficient `a_0` of the constant term to zero,
     /// effectively creating a zero-hole univariate polynomial.
     pub fn to_zero_hole(&mut self) {
-        self.set_coefficient(0, F::ZERO);
+        let updated = self.set_coefficient(0, F::ZERO);
+        debug_assert!(updated)
     }
 
     /// Returns true iff the coefficient `a_0` of the constant term is zero.
@@ -484,10 +486,10 @@ mod tests {
     fn test_set_coefficients() {
         let mut p = Polynomial::with_coefficients(scalars(&[1, 2, 3]));
 
-        p.set_coefficient(3, scalar(4));
+        assert!(!p.set_coefficient(3, scalar(4)));
         assert_eq!(p.a, scalars(&[1, 2, 3]));
 
-        p.set_coefficient(1, scalar(4));
+        assert!(p.set_coefficient(1, scalar(4)));
         assert_eq!(p.a, scalars(&[1, 4, 3]));
     }
 

secret-sharing/src/shamir/dealer.rs

@@ -18,7 +18,8 @@ where
     /// Creates a new dealer with a predefined shared secret.
     pub fn new(threshold: u8, secret: F, rng: &mut impl RngCore) -> Self {
         let mut sharer = Self::random(threshold, rng);
-        sharer.poly.set_coefficient(0, secret);
+        let updated = sharer.poly.set_coefficient(0, secret);
+        debug_assert!(updated);
         sharer
     }
 

secret-sharing/src/vss/matrix.rs

@@ -375,8 +375,8 @@ mod tests {
         // Two non-zero coefficients (fast).
         let mut rng: StdRng = SeedableRng::from_seed([1u8; 32]);
         let mut bp = BivariatePolynomial::<p384::Scalar>::zero(2, 3);
-        bp.set_coefficient(0, 0, p384::Scalar::ONE);
-        bp.set_coefficient(2, 2, p384::Scalar::ONE.double());
+        assert!(bp.set_coefficient(0, 0, p384::Scalar::ONE));
+        assert!(bp.set_coefficient(2, 2, p384::Scalar::ONE.double()));
 
         let vm = VerificationMatrix::<p384::ProjectivePoint>::from(&bp);
         assert_eq!(vm.m.len(), 3);