fix: VID ADVZ allow zero-length payload

CHANGELOG.md

@@ -18,6 +18,7 @@ and follow [semantic versioning](https://semver.org/) for our releases.
 ### Fixed
 
 - [#243](https://github.com/EspressoSystems/jellyfish/pull/243) fixes bug in MerkleTreeGadget implementation for SparseRescueMerkleTree.
+- [#377](https://github.com/EspressoSystems/jellyfish/pull/377) fix: VID ADVZ allow zero-length payload
 
 ### Added
 

primitives/src/pcs/univariate_kzg/mod.rs

@@ -353,12 +353,14 @@ where
     ) -> Result<GeneralDensePolynomial<E::G1, F>, PCSError> {
         // First, pad to power_of_two, since Toeplitz mul only works for 2^k
         let mut padded_coeffs: Vec<F> = poly_coeffs.to_vec();
-        let padded_degree = (padded_coeffs.len() - 1)
+        let padded_degree = padded_coeffs
+            .len()
+            .saturating_sub(1)
             .checked_next_power_of_two()
             .ok_or_else(|| {
                 PCSError::InvalidParameters(ark_std::format!(
                     "Next power of two overflows! Got: {}",
-                    (padded_coeffs.len() - 1)
+                    padded_coeffs.len().saturating_sub(1)
                 ))
             })?;
         let padded_len = padded_degree + 1;

primitives/src/vid/advz.rs

@@ -275,7 +275,11 @@ where
     /// Same as [`VidScheme::disperse`] except `payload` is a slice of
     /// field elements.
     pub fn disperse_from_elems(&self, payload: &[P::Evaluation]) -> VidResult<VidDisperse<Self>> {
-        let num_polys = (payload.len() - 1) / self.payload_chunk_size + 1;
+        let num_polys = if payload.is_empty() {
+            0
+        } else {
+            (payload.len() - 1) / self.payload_chunk_size + 1
+        };
         let domain = P::multi_open_rou_eval_domain(self.payload_chunk_size, self.num_storage_nodes)
             .map_err(vid)?;
 

primitives/tests/advz.rs

@@ -13,7 +13,7 @@ mod vid;
 fn round_trip() {
     // play with these items
     let vid_sizes = [(2, 3), (5, 9)];
-    let byte_lens = [2, 16, 32, 47, 48, 49, 64, 100, 400];
+    let byte_lens = [0, 1, 2, 16, 32, 47, 48, 49, 64, 100, 400];
 
     // more items as a function of the above
     let supported_degree = vid_sizes.iter().max_by_key(|v| v.0).unwrap().0;