added padding advice column in Exp Circuit

src/zkevm_specs/evm/typing.py

@@ -742,23 +742,21 @@ def add(self, data: bytes, r: FQ) -> KeccakCircuit:
 
 class ExpCircuit:
     rows: List[ExpCircuitRow]
-    pad_rows: List[ExpCircuitRow]
+    max_exp_steps: int
+    OFFSET_INCREMENT = 7
 
-    def __init__(self, pad_rows: Optional[List[ExpCircuitRow]] = None) -> None:
+    def __init__(self, max_exp_steps: int = 100) -> None:
         self.rows = []
-        self.pad_rows = []
-        if pad_rows is not None:
-            self.pad_rows = pad_rows
+        self.max_exp_steps = max_exp_steps
 
     def table(self) -> Sequence[ExpCircuitRow]:
-        return self.rows + self.pad_rows
+        return self.rows
 
     def add_event(self, base: int, exponent: int, randomness: FQ, identifier: IntOrFQ):
         steps: List[Tuple[int, int, int]] = []
         exponentiation = self._exp_by_squaring(base, exponent, steps)
         steps.reverse()
         self._append_steps(base, exponent, exponentiation, steps, randomness, identifier)
-        self._append_padding_row(identifier)
         return self
 
     def _exp_by_squaring(self, base: int, exponent: int, steps: List[Tuple[int, int, int]]):
@@ -816,24 +814,28 @@ def _append_steps(
                 # exponent is odd
                 exponent = exponent - 1
 
-    def _append_padding_row(self, identifier: IntOrFQ):
-        self.rows.append(
-            ExpCircuitRow(
-                q_usable=FQ.zero(),
-                is_step=FQ.zero(),
-                identifier=FQ(identifier),
-                is_last=FQ.zero(),
-                base=RLC(0),
-                exponent=RLC(0),
-                exponentiation=RLC(0),
-                a=RLC(0),
-                b=RLC(0),
-                c=RLC(0),
-                d=RLC(0),
-                q=RLC(0),
-                r=RLC(0),
+    def fill_dummy_events(self):
+        max_exp_rows = self.max_exp_steps * self.OFFSET_INCREMENT
+        rows_left = max_exp_rows - len(self.rows)
+        for i in range(rows_left):
+            self.rows.append(
+                ExpCircuitRow(
+                    q_usable=FQ.one(),
+                    is_step=FQ.zero(),
+                    identifier=FQ.zero(),
+                    is_last=FQ.zero(),
+                    base=RLC(1),
+                    exponent=RLC(1),
+                    exponentiation=RLC(1),
+                    a=RLC(1),
+                    b=RLC(1),
+                    c=RLC(0),
+                    d=RLC(1),
+                    q=RLC(0),
+                    r=RLC(1),
+                )
             )
-        )
+        return self
 
     def _append_step(
         self,

src/zkevm_specs/exp_circuit.py

@@ -29,9 +29,6 @@ def verify_step(cs: ConstraintSystem, rows: List[ExpCircuitRow]):
         cs.constrain_bool(rows[0].is_last)
         # remainder (r), i.e. odd/even parity of exponent is boolean.
         cs.constrain_bool(rows[0].r)
-        # is_last == 1 is followed by unusable row.
-        # is_last == 0 is following by usable row.
-        cs.constrain_equal(rows[0].is_last, (1 - rows[1].q_usable))
         # multiplication is assigned correctly
         _overflow, carry_lo_hi, additional_constraints = mul_add_words(
             rows[0].a, rows[0].b, rows[0].c, rows[0].d

tests/evm/test_exp.py

@@ -69,7 +69,9 @@ def test_exp(base: int, exponent: int):
         .stack_write(CALL_ID, 1023, exponentiation_rlc)
     )
 
-    exp_circuit = ExpCircuit().add_event(base, exponent, randomness, rw_dict.rw_counter)
+    exp_circuit = (
+        ExpCircuit().add_event(base, exponent, randomness, rw_dict.rw_counter).fill_dummy_events()
+    )
 
     tables = Tables(
         block_table=set(Block().table_assignments(randomness)),