Improve constant folding (Fix #820)

slither/slithir/variables/constant.py

@@ -1,10 +1,10 @@
-from functools import total_ordering
 from decimal import Decimal
+from functools import total_ordering
 
-from slither.slithir.variables.variable import SlithIRVariable
-from slither.slithir.exceptions import SlithIRError
 from slither.core.solidity_types.elementary_type import ElementaryType, Int, Uint
+from slither.slithir.variables.variable import SlithIRVariable
 from slither.utils.arithmetic import convert_subdenomination
+from slither.utils.integer_conversion import convert_string_to_int
 
 
 @total_ordering
@@ -25,26 +25,7 @@ class Constant(SlithIRVariable):
             assert isinstance(constant_type, ElementaryType)
             self._type = constant_type
             if constant_type.type in Int + Uint + ["address"]:
-                if val.startswith("0x") or val.startswith("0X"):
-                    self._val = int(val, 16)
-                else:
-                    if "e" in val or "E" in val:
-                        base, expo = val.split("e") if "e" in val else val.split("E")
-                        base, expo = Decimal(base), int(expo)
-                        # The resulting number must be < 2**256-1, otherwise solc
-                        # Would not be able to compile it
-                        # 10**77 is the largest exponent that fits
-                        # See https://github.com/ethereum/solidity/blob/9e61f92bd4d19b430cb8cb26f1c7cf79f1dff380/libsolidity/ast/Types.cpp#L1281-L1290
-                        if expo > 77:
-                            if base != Decimal(0):
-                                raise SlithIRError(
-                                    f"{base}e{expo} is too large to fit in any Solidity integer size"
-                                )
-                            self._val = 0
-                        else:
-                            self._val = int(Decimal(base) * Decimal(10 ** expo))
-                    else:
-                        self._val = int(Decimal(val))
+                self._val = convert_string_to_int(val)
             elif constant_type.type == "bool":
                 self._val = (val == "true") | (val == "True")
             else:

slither/utils/integer_conversion.py

@@ -0,0 +1,25 @@
+from decimal import Decimal
+
+from slither.exceptions import SlitherError
+
+
+def convert_string_to_int(val: str) -> int:
+    if val.startswith("0x") or val.startswith("0X"):
+        return int(val, 16)
+
+    if "e" in val or "E" in val:
+        base, expo = val.split("e") if "e" in val else val.split("E")
+        base, expo = Decimal(base), int(expo)
+        # The resulting number must be < 2**256-1, otherwise solc
+        # Would not be able to compile it
+        # 10**77 is the largest exponent that fits
+        # See https://github.com/ethereum/solidity/blob/9e61f92bd4d19b430cb8cb26f1c7cf79f1dff380/libsolidity/ast/Types.cpp#L1281-L1290
+        if expo > 77:
+            if base != Decimal(0):
+                raise SlitherError(
+                    f"{base}e{expo} is too large to fit in any Solidity integer size"
+                )
+            return 0
+        return int(Decimal(base) * Decimal(10 ** expo))
+
+    return int(Decimal(val))

slither/visitors/expression/constants_folding.py

@@ -1,4 +1,5 @@
 from slither.core.expressions import BinaryOperationType, Literal
+from slither.utils.integer_conversion import convert_string_to_int
 from slither.visitors.expression.expression import ExpressionVisitor
 
 
@@ -36,7 +37,7 @@ class ConstantFolding(ExpressionVisitor):
         if not isinstance(expr, Literal):
             cf = ConstantFolding(expr, self._type)
             expr = cf.result()
-        set_val(expression, int(expr.value))
+        set_val(expression, convert_string_to_int(expr.value))
 
     def _post_binary_operation(self, expression):
         left = get_val(expression.expression_left)