Fix fft helper and add basic test

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

@@ -110,28 +110,31 @@ def g2_lincomb(points: Sequence[KZGCommitment], scalars: Sequence[BLSFieldElemen
 #### `_fft_field`
 
 ```python
-def _fft_field(vals, roots_of_unity):
-    if len(vals) == 0:
+def _fft_field(vals: Sequence[BLSFieldElement],
+               roots_of_unity: Sequence[BLSFieldElement]) -> Sequence[BLSFieldElement]:
+    if len(vals) == 1:
         return vals
     L = _fft_field(vals[::2], roots_of_unity[::2])
     R = _fft_field(vals[1::2], roots_of_unity[::2])
-    o = [0 for i in vals]
+    o = [BLSFieldElement(0) for _ in vals]
     for i, (x, y) in enumerate(zip(L, R)):
-        y_times_root = int(y) * int(roots_of_unity[i]) % BLS_MODULUS
-        o[i] = (x + y_times_root) % BLS_MODULUS
-        o[i + len(L)] = (x - y_times_root + BLS_MODULUS) % BLS_MODULUS
+        y_times_root = (int(y) * int(roots_of_unity[i])) % BLS_MODULUS
+        o[i] = BLSFieldElement((int(x) + y_times_root) % BLS_MODULUS)
+        o[i + len(L)] = BLSFieldElement((int(x) - y_times_root + BLS_MODULUS) % BLS_MODULUS)
     return o
 ```
 
 #### `fft_field`
 
 ```python
-def fft_field(vals, roots_of_unity, inv=False):
+def fft_field(vals: Sequence[BLSFieldElement],
+              roots_of_unity: Sequence[BLSFieldElement],
+              inv: bool=False) -> Sequence[BLSFieldElement]:
     if inv:
         # Inverse FFT
         invlen = pow(len(vals), BLS_MODULUS - 2, BLS_MODULUS)
-        return [(x * invlen) % BLS_MODULUS for x in
-                _fft_field(vals, roots_of_unity[0:1] + roots_of_unity[:0:-1])]
+        return [BLSFieldElement((int(x) * invlen) % BLS_MODULUS)
+                for x in _fft_field(vals, roots_of_unity[0:1] + roots_of_unity[:0:-1])]
     else:
         # Regular FFT
         return _fft_field(vals, roots_of_unity)
@@ -272,7 +275,7 @@ def evaluate_polynomialcoeff(polynomial_coeff: PolynomialCoeff, z: BLSFieldEleme
     """
     y = 0
     for coef in polynomial_coeff[::-1]:
-        y = (int(y) * int(z) + coef) % BLS_MODULUS
+        y = (int(y) * int(z) + int(coef)) % BLS_MODULUS
     return BLSFieldElement(y % BLS_MODULUS)
 ```
 

tests/core/pyspec/eth2spec/test/context.py

@@ -8,7 +8,7 @@ from eth2spec.utils import bls
 from .exceptions import SkippedTest
 from .helpers.constants import (
     PHASE0, ALTAIR, BELLATRIX, CAPELLA, DENEB,
-    EIP6110, EIP7002,
+    EIP6110, EIP7002, PEERDAS,
     WHISK,
     MINIMAL,
     ALL_PHASES,
@@ -510,6 +510,7 @@ with_deneb_and_later = with_all_phases_from(DENEB)
 with_eip6110_and_later = with_all_phases_from(EIP6110)
 with_eip7002_and_later = with_all_phases_from(EIP7002)
 with_whisk_and_later = with_all_phases_from(WHISK, all_phases=ALLOWED_TEST_RUNNER_FORKS)
+with_peerdas_and_later = with_all_phases_from(PEERDAS, all_phases=ALLOWED_TEST_RUNNER_FORKS)
 
 
 class quoted_str(str):

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

@@ -0,0 +1,30 @@
+from eth2spec.test.context import (
+    spec_test,
+    single_phase,
+    with_peerdas_and_later,
+)
+from eth2spec.test.helpers.sharding import (
+    get_sample_blob,
+)
+
+
+@with_peerdas_and_later
+@spec_test
+@single_phase
+def test_fft(spec):
+    vals = [int.from_bytes(x, spec.KZG_ENDIANNESS) for x in spec.KZG_SETUP_G1_MONOMIAL]
+    roots_of_unity = spec.ROOTS_OF_UNITY
+    result = spec.fft_field(vals, roots_of_unity)
+    assert len(result) == len(vals)
+    # TODO: add more assertions?
+
+
+@with_peerdas_and_later
+@spec_test
+@single_phase
+def test_compute_and_verify_cells_and_proofs(spec):
+    blob = get_sample_blob(spec)
+    commitment = spec.blob_to_kzg_commitment(blob)
+    cells, proofs = spec.compute_cells_and_proofs(blob)
+    cell_id = 0
+    assert spec.verify_cell_proof(commitment, cell_id, cells[cell_id], proofs[cell_id])

tests/core/pyspec/eth2spec/utils/bls.py

@@ -4,6 +4,7 @@ from py_ecc.optimized_bls12_381 import (  # noqa: F401
     G1 as py_ecc_G1,
     G2 as py_ecc_G2,
     Z1 as py_ecc_Z1,
+    Z2 as py_ecc_Z2,
     add as py_ecc_add,
     multiply as py_ecc_mul,
     neg as py_ecc_neg,
@@ -243,6 +244,15 @@ def Z1():
     return py_ecc_Z1
 
 
+def Z2():
+    """
+    Returns the identity point in G2
+    """
+    if bls == arkworks_bls or bls == fastest_bls:
+        return arkworks_G2.identity()
+    return py_ecc_Z2
+
+
 def G1():
     """
     Returns the chosen generator point in G1