fix `field::split_data_into_field_elements`

src/fec.rs

@@ -30,7 +30,7 @@ impl Shard {
             _ => {
                 let alpha = E::ScalarField::from_le_bytes_mod_order(&u32_to_u8_vec(alpha));
 
-                let elements = field::split_data_into_field_elements::<E>(&self.bytes, 1)
+                let elements = field::split_data_into_field_elements::<E>(&self.bytes, 1, true)
                     .iter()
                     .map(|e| e.mul(alpha))
                     .collect::<Vec<_>>();
@@ -66,8 +66,8 @@ impl Shard {
             let alpha = E::ScalarField::from_le_bytes_mod_order(&u32_to_u8_vec(alpha));
             let beta = E::ScalarField::from_le_bytes_mod_order(&u32_to_u8_vec(beta));
 
-            let elements_self = field::split_data_into_field_elements::<E>(&self.bytes, 1);
-            let elements_other = field::split_data_into_field_elements::<E>(&other.bytes, 1);
+            let elements_self = field::split_data_into_field_elements::<E>(&self.bytes, 1, true);
+            let elements_other = field::split_data_into_field_elements::<E>(&other.bytes, 1, true);
 
             elements_self
                 .iter()

src/field.rs

@@ -11,10 +11,16 @@ use ark_std::One;
 pub(crate) fn split_data_into_field_elements<E: Pairing>(
     bytes: &[u8],
     modulus: usize,
+    one_more: bool,
 ) -> Vec<E::ScalarField> {
-    let mut elements = Vec::new();
+    let bytes_per_element = if one_more {
+        (E::ScalarField::MODULUS_BIT_SIZE as usize) / 8 + 1
+    } else {
+        (E::ScalarField::MODULUS_BIT_SIZE as usize) / 8
+    };
 
-    for chunk in bytes.chunks((E::ScalarField::MODULUS_BIT_SIZE as usize) / 8 + 1) {
+    let mut elements = Vec::new();
+    for chunk in bytes.chunks(bytes_per_element) {
         elements.push(E::ScalarField::from_le_bytes_mod_order(chunk));
     }
 
@@ -113,7 +119,7 @@ mod tests {
     }
 
     fn split_data_template<E: Pairing>(bytes: &[u8], modulus: usize, exact_length: Option<usize>) {
-        let elements = field::split_data_into_field_elements::<E>(bytes, modulus);
+        let elements = field::split_data_into_field_elements::<E>(bytes, modulus, false);
         assert!(
             elements.len() % modulus == 0,
             "number of elements should be divisible by {}, found {}",

src/lib.rs

@@ -96,7 +96,7 @@ where
     info!("encoding and proving {} bytes", bytes.len());
 
     debug!("splitting bytes into polynomials");
-    let elements = field::split_data_into_field_elements::<E>(bytes, k);
+    let elements = field::split_data_into_field_elements::<E>(bytes, k, false);
     let nb_polynomials = elements.len() / k;
     let polynomials = match field::build_interleaved_polynomials::<E, P>(&elements, nb_polynomials)
     {
@@ -148,7 +148,7 @@ where
     P: DenseUVPolynomial<E::ScalarField, Point = E::ScalarField>,
     for<'a, 'b> &'a P: Div<&'b P, Output = P>,
 {
-    let elements = field::split_data_into_field_elements::<E>(&block.shard.bytes, 1);
+    let elements = field::split_data_into_field_elements::<E>(&block.shard.bytes, 1, true);
     let polynomial = P::from_coefficients_vec(elements);
     let (commit, _) = KZG10::<E, P>::commit(verifier_key, &polynomial, None, None)?;