Update algorithm & remove check

Author: jtraglia

specs/_features/eip7594/polynomial-commitments-sampling.md

@@ -511,10 +511,6 @@ def verify_cell_kzg_proof_batch_impl(row_commitments: Sequence[KZGCommitment],
     n = FIELD_ELEMENTS_PER_CELL
     num_rows = len(row_commitments)
 
-    # Given zero cells, the result is true
-    if num_cells == 0:
-        return True
-
     # Step 1: Compute a challenge r and its powers r^0, ..., r^{num_cells-1}
     r = compute_verify_cell_kzg_proof_batch_challenge(
         row_commitments,
@@ -544,7 +540,7 @@ def verify_cell_kzg_proof_batch_impl(row_commitments: Sequence[KZGCommitment],
 
     # Step 4.2: Compute RLI = [sum_k r^k interpolation_poly_k(s)]
     # Note: an efficient implementation would use the IDFT based method explained in the blog post
-    sum_interp_polys_coeff = [0]
+    sum_interp_polys_coeff = [0] * n
     for k in range(num_cells):
         interp_poly_coeff = interpolate_polynomialcoeff(coset_for_cell(column_indices[k]), cosets_evals[k])
         interp_poly_scaled_coeff = multiply_polynomialcoeff([r_powers[k]], interp_poly_coeff)

tests/core/pyspec/eth2spec/test/eip7594/unittests/polynomial_commitments/test_polynomial_commitments.py

@@ -122,6 +122,20 @@ def test_verify_cell_kzg_proof(spec):
     assert spec.verify_cell_kzg_proof(commitment, cell_index, cells[cell_index], proofs[cell_index])
 
 
+@with_eip7594_and_later
+@spec_test
+@single_phase
+def test_verify_cell_kzg_proof_batch_zero_cells(spec):
+    # Verify with zero cells should return true
+    assert spec.verify_cell_kzg_proof_batch(
+        row_commitments_bytes=[],
+        row_indices=[],
+        column_indices=[],
+        cells=[],
+        proofs_bytes=[],
+    )
+
+
 @with_eip7594_and_later
 @spec_test
 @single_phase