mirror of
https://github.com/ethereum/solidity
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38 lines
873 B
Python
38 lines
873 B
Python
from opcodes import AND, ISZERO, GT, DIV
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from rule import Rule
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from util import BVUnsignedUpCast, BVUnsignedMax
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from z3 import BitVec, Not, BVMulNoOverflow
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"""
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Overflow checked unsigned integer multiplication.
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"""
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# Approximation with 16-bit base types.
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n_bits = 16
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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(BVMulNoOverflow(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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# Constants
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maxValue = BVUnsignedMax(type_bits, n_bits)
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# Overflow check in YulUtilFunction::overflowCheckedIntMulFunction
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overflow_check = AND(ISZERO(ISZERO(X)), GT(Y, DIV(maxValue, X)))
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rule.check(overflow_check != 0, actual_overflow)
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type_bits *= 2
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