From 036f7d62f418ce55fd845df1ef8fbf472314a6ef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emilio=20L=C3=B3pez?= <emilio.lopez@trailofbits.com>
Date: Sun, 18 Sep 2022 10:56:34 -0300
Subject: [PATCH] Replace Decimal with Fraction

Fractions are arbitrary-precision and will not cause truncated values.
---
 slither/slithir/variables/constant.py            |  4 ++--
 slither/utils/__init__.py                        |  3 ---
 slither/utils/arithmetic.py                      | 12 +++---------
 slither/utils/integer_conversion.py              | 10 +++++-----
 slither/visitors/expression/constants_folding.py |  6 +++---
 5 files changed, 13 insertions(+), 22 deletions(-)

diff --git a/slither/slithir/variables/constant.py b/slither/slithir/variables/constant.py
index 09a5ee34f..52cabf701 100644
--- a/slither/slithir/variables/constant.py
+++ b/slither/slithir/variables/constant.py
@@ -1,4 +1,4 @@
-from decimal import Decimal
+from fractions import Fraction
 from functools import total_ordering
 
 from slither.core.solidity_types.elementary_type import ElementaryType, Int, Uint
@@ -33,7 +33,7 @@ class Constant(SlithIRVariable):
         else:
             if val.isdigit():
                 self._type = ElementaryType("uint256")
-                self._val = int(Decimal(val))
+                self._val = int(Fraction(val))
             else:
                 self._type = ElementaryType("string")
                 self._val = val
diff --git a/slither/utils/__init__.py b/slither/utils/__init__.py
index 86427ca2e..e69de29bb 100644
--- a/slither/utils/__init__.py
+++ b/slither/utils/__init__.py
@@ -1,3 +0,0 @@
-from slither.utils.arithmetic import configure_decimal_precision
-
-configure_decimal_precision()
\ No newline at end of file
diff --git a/slither/utils/arithmetic.py b/slither/utils/arithmetic.py
index 83c5be544..69684d103 100644
--- a/slither/utils/arithmetic.py
+++ b/slither/utils/arithmetic.py
@@ -1,13 +1,7 @@
-from decimal import Decimal, getcontext
+from fractions import Fraction
 
 from slither.exceptions import SlitherException
 
-def configure_decimal_precision():
-    # Configure decimal precision high enough for 2 ** 256
-    # Otherwise, large constant arithmetic may get truncated
-    if getcontext().prec < 80:
-        getcontext().prec = 80
-
 # pylint: disable=too-many-branches
 def convert_subdenomination(
     value: str, sub: str
@@ -15,9 +9,9 @@ def convert_subdenomination(
 
     # to allow 0.1 ether conversion
     if value[0:2] == "0x":
-        decimal_value = Decimal(int(value, 16))
+        decimal_value = Fraction(int(value, 16))
     else:
-        decimal_value = Decimal(value)
+        decimal_value = Fraction(value)
     if sub == "wei":
         return int(decimal_value)
     if sub == "gwei":
diff --git a/slither/utils/integer_conversion.py b/slither/utils/integer_conversion.py
index 8481e8641..a410a956b 100644
--- a/slither/utils/integer_conversion.py
+++ b/slither/utils/integer_conversion.py
@@ -1,4 +1,4 @@
-from decimal import Decimal
+from fractions import Fraction
 from typing import Union
 
 from slither.exceptions import SlitherError
@@ -12,17 +12,17 @@ def convert_string_to_int(val: Union[str, int]) -> int:
 
     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)
+        base, expo = Fraction(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):
+            if base != Fraction(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(Fraction(base) * Fraction(10**expo))
 
-    return int(Decimal(val))
+    return int(Fraction(val))
diff --git a/slither/visitors/expression/constants_folding.py b/slither/visitors/expression/constants_folding.py
index 27ff9b592..2da1d7304 100644
--- a/slither/visitors/expression/constants_folding.py
+++ b/slither/visitors/expression/constants_folding.py
@@ -1,4 +1,4 @@
-from decimal import Decimal, InvalidOperation
+from fractions import Fraction
 from slither.core.expressions import BinaryOperationType, Literal, UnaryOperationType
 from slither.utils.integer_conversion import convert_string_to_int
 from slither.visitors.expression.expression import ExpressionVisitor
@@ -79,8 +79,8 @@ class ConstantFolding(ExpressionVisitor):
 
     def _post_literal(self, expression):
         try:
-            set_val(expression, Decimal(expression.value))
-        except InvalidOperation:
+            set_val(expression, Fraction(expression.value))
+        except ValueError:
             raise NotConstant
 
     def _post_assignement_operation(self, expression):