mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
47 lines
1.4 KiB
Python
47 lines
1.4 KiB
Python
from opcodes import AND, SDIV, MUL, EQ, ISZERO, OR, SLT
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from rule import Rule
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from util import BVSignedUpCast, BVSignedMin, BVSignedCleanupFunction
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from z3 import BVMulNoOverflow, BVMulNoUnderflow, BitVec, Not, Or
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"""
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Overflow checked signed integer multiplication.
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"""
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# Approximation with 16-bit base types.
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n_bits = 12
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for type_bits in [4, 6, 8, 12]:
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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(BVMulNoOverflow(X_short, Y_short, True))
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actual_underflow = Not(BVMulNoUnderflow(X_short, Y_short))
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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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product_raw = MUL(X, Y)
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#remove any overflown bits
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product = BVSignedCleanupFunction(product_raw, type_bits)
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# Constants
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min_value = BVSignedMin(type_bits, n_bits)
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# Overflow and underflow checks in YulUtilFunction::overflowCheckedIntMulFunction
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if type_bits > n_bits / 2:
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sol_overflow_check_1 = ISZERO(OR(ISZERO(X), EQ(Y, SDIV(product, X))))
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if type_bits == n_bits:
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sol_overflow_check_2 = AND(SLT(X, 0), EQ(Y, min_value))
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sol_overflow_check = Or(sol_overflow_check_1 != 0, sol_overflow_check_2 != 0)
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else:
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sol_overflow_check = (sol_overflow_check_1 != 0)
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else:
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sol_overflow_check = (ISZERO(EQ(product, product_raw)) != 0)
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rule.check(Or(actual_overflow, actual_underflow), sol_overflow_check)
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