mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
37 lines
776 B
Python
37 lines
776 B
Python
from opcodes import LT
|
|
from rule import Rule
|
|
from util import BVUnsignedMax, BVUnsignedUpCast
|
|
from z3 import BVSubNoUnderflow, BitVec, Not
|
|
|
|
"""
|
|
Overflow checked unsigned integer subtraction.
|
|
"""
|
|
|
|
n_bits = 256
|
|
type_bits = 8
|
|
|
|
while type_bits <= n_bits:
|
|
|
|
rule = Rule()
|
|
|
|
# Input vars
|
|
X_short = BitVec('X', type_bits)
|
|
Y_short = BitVec('Y', type_bits)
|
|
|
|
# Z3's overflow condition
|
|
actual_overflow = Not(BVSubNoUnderflow(X_short, Y_short, False))
|
|
|
|
# cast to full n_bits values
|
|
X = BVUnsignedUpCast(X_short, n_bits)
|
|
Y = BVUnsignedUpCast(Y_short, n_bits)
|
|
|
|
# Constants
|
|
maxValue = BVUnsignedMax(type_bits, n_bits)
|
|
|
|
# Overflow check in YulUtilFunction::overflowCheckedIntSubFunction
|
|
overflow_check = LT(X, Y)
|
|
|
|
rule.check(overflow_check != 0, actual_overflow)
|
|
|
|
type_bits *= 2
|