mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
46 lines
1.2 KiB
Python
46 lines
1.2 KiB
Python
from opcodes import AND, ISZERO, SLT, SGT, SUB
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from rule import Rule
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from util import BVSignedMax, BVSignedMin, BVSignedUpCast
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from z3 import BitVec, BVSubNoOverflow, BVSubNoUnderflow, Not
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"""
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Overflow checked signed 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 and underflow conditions
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actual_overflow = Not(BVSubNoOverflow(X_short, Y_short))
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actual_underflow = Not(BVSubNoUnderflow(X_short, Y_short, True))
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# cast to full n_bits values
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X = BVSignedUpCast(X_short, n_bits)
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Y = BVSignedUpCast(Y_short, n_bits)
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diff = SUB(X, Y)
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# Constants
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maxValue = BVSignedMax(type_bits, n_bits)
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minValue = BVSignedMin(type_bits, n_bits)
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# Overflow and underflow checks in YulUtilFunction::overflowCheckedIntSubFunction
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if type_bits == 256:
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underflow_check = AND(ISZERO(SLT(Y, 0)), SGT(diff, X))
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overflow_check = AND(SLT(Y, 0), SLT(diff, X))
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else:
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underflow_check = SLT(diff, minValue)
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overflow_check = SGT(diff, maxValue)
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type_bits += 8
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rule.check(actual_underflow, underflow_check != 0)
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rule.check(actual_overflow, overflow_check != 0)
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