feat: optimize int256 bounds checks

vyperlang · Apr 14, 2021 · 2ff7329 · 2ff7329
1 parent 94dbf89
commit 2ff7329
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Showing 2 changed files with 26 additions and 8 deletions.
diff --git a/vyper/functions/convert.py b/vyper/functions/convert.py
@@ -5,6 +5,7 @@
 from vyper import ast as vy_ast
 from vyper.exceptions import InvalidLiteral, StructureException, TypeMismatch
 from vyper.functions.signatures import signature
+from vyper.opcodes import version_check
 from vyper.parser.arg_clamps import address_clamp, int128_clamp
 from vyper.parser.parser_utils import LLLnode, byte_array_to_num, getpos
 from vyper.types import BaseType, ByteArrayType, StringType, get_type
@@ -190,9 +191,12 @@ def to_int256(expr, args, kwargs, context):
         return LLLnode.from_list(in_arg, typ=BaseType("int256"), pos=getpos(expr))
 
     elif isinstance(in_arg, LLLnode) and input_type == "uint256":
-        # TODO bitshift to save gas on the bounds check
+        if version_check(begin="constantinople"):
+            upper_bound = ["shl", 255, 1]
+        else:
+            upper_bound = -(2 ** 255)
         return LLLnode.from_list(
-            ["uclample", in_arg, SizeLimits.MAX_INT256], typ=BaseType("int256"), pos=getpos(expr)
+            ["uclamplt", in_arg, upper_bound], typ=BaseType("int256"), pos=getpos(expr)
         )
 
     elif isinstance(in_arg, LLLnode) and input_type == "decimal":

diff --git a/vyper/parser/expr.py b/vyper/parser/expr.py
@@ -559,12 +559,19 @@ def parse_BinOp(self):
                 ]
 
             elif ltyp == "int256":
+                if version_check(begin="constantinople"):
+                    upper_bound = ["shl", 255, 1]
+                else:
+                    upper_bound = -(2 ** 255)
                 if not left.typ.is_literal and not right.typ.is_literal:
-                    bounds_check = ["assert", ["or", ["ne", "l", -1], ["ne", "r", -(2 ** 255)]]]
+                    bounds_check = [
+                        "assert",
+                        ["or", ["ne", "l", ["not", 0]], ["ne", "r", upper_bound]],
+                    ]
                 elif left.typ.is_literal and left.value == -1:
-                    bounds_check = ["assert", ["ne", "r", -(2 ** 255)]]
+                    bounds_check = ["assert", ["ne", "r", upper_bound]]
                 elif right.typ.is_literal and right.value == -(2 ** 255):
-                    bounds_check = ["assert", ["ne", "l", -1]]
+                    bounds_check = ["assert", ["ne", "l", ["not", 0]]]
                 else:
                     bounds_check = "pass"
                 arith = [
@@ -610,12 +617,19 @@ def parse_BinOp(self):
                 arith = ["div", "l", divisor]
 
             elif ltyp == "int256":
+                if version_check(begin="constantinople"):
+                    upper_bound = ["shl", 255, 1]
+                else:
+                    upper_bound = -(2 ** 255)
                 if not left.typ.is_literal and not right.typ.is_literal:
-                    bounds_check = ["assert", ["or", ["ne", "r", -1], ["ne", "l", -(2 ** 255)]]]
+                    bounds_check = [
+                        "assert",
+                        ["or", ["ne", "r", ["not", 0]], ["ne", "l", upper_bound]],
+                    ]
                 elif left.typ.is_literal and left.value == -(2 ** 255):
-                    bounds_check = ["assert", ["ne", "r", -1]]
+                    bounds_check = ["assert", ["ne", "r", ["not", 0]]]
                 elif right.typ.is_literal and right.value == -1:
-                    bounds_check = ["assert", ["ne", "l", -(2 ** 255)]]
+                    bounds_check = ["assert", ["ne", "l", upper_bound]]
                 else:
                     bounds_check = "pass"
                 arith = ["seq", bounds_check, ["sdiv", "l", divisor]]