solidity/test/formal/checked_uint_sub.py

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from rule import Rule
from opcodes import *
from util import *
"""
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