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