logic change to mod exp revert rules

core/vm/contracts_zkevm.go

@@ -389,22 +389,31 @@ func (c *bigModExp_zkevm) Run(input []byte) ([]byte, error) {
 	} else {
 		input = input[:0]
 	}
-	// Handle a special case when both the base and mod length is zero
-	if baseLen == 0 && modLen == 0 {
+
+	if modLen == 0 {
 		return []byte{}, nil
 	}
+
 	// Retrieve the operands and execute the exponentiation
 	var (
-		base = new(big.Int).SetBytes(getData(input, 0, baseLen))
-		exp  = new(big.Int).SetBytes(getData(input, baseLen, expLen))
-		mod  = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
-		v    []byte
+		base       = new(big.Int).SetBytes(getData(input, 0, baseLen))
+		exp        = new(big.Int).SetBytes(getData(input, baseLen, expLen))
+		mod        = new(big.Int).SetBytes(getData(input, baseLen+expLen, modLen))
+		v          []byte
+		baseBitLen = base.BitLen()
+		expBitLen  = exp.BitLen()
+		modBitLen  = mod.BitLen()
 	)
 
+	if baseBitLen == 0 {
+		if modBitLen > 8192 {
+			return nil, ErrExecutionReverted
+		} else {
+			return []byte{}, nil
+		}
+	}
+
 	// limit to 8192 bits for base, exp, and mod in ZK
-	baseBitLen := base.BitLen()
-	expBitLen := exp.BitLen()
-	modBitLen := mod.BitLen()
 	if baseBitLen > 8192 || expBitLen > 8192 || modBitLen > 8192 {
 		return nil, ErrExecutionReverted
 	}