mirror of
https://github.com/ethereum/solidity
synced 2023-10-03 13:03:40 +00:00
46 lines
810 B
Python
46 lines
810 B
Python
from opcodes import AND, SHL, SHR
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from rule import Rule
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from z3 import BitVec, BitVecVal, If, Int2BV, IntVal, UGT, ULT
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"""
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Rule:
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mask = shlWorkaround(u256(-1), unsigned(A.d())) >> unsigned(B.d())
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SHR(B, SHL(A, X)) -> AND(SH[L/R]([B - A / A - B], X), Mask)
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Requirements:
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A < BitWidth
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B < BitWidth
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"""
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rule = Rule()
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n_bits = 64
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# Input vars
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X = BitVec('X', n_bits)
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A = BitVec('A', n_bits)
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B = BitVec('B', n_bits)
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# Constants
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BitWidth = BitVecVal(n_bits, n_bits)
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# Requirements
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rule.require(ULT(A, BitWidth))
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rule.require(ULT(B, BitWidth))
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# Non optimized result
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nonopt = SHR(B, SHL(A, X))
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# Optimized result
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Mask = SHR(B, SHL(A, Int2BV(IntVal(-1), n_bits)))
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opt = If(
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UGT(A, B),
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AND(SHL(A - B, X), Mask),
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If(
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UGT(B, A),
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AND(SHR(B - A, X), Mask),
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AND(X, Mask)
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)
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)
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rule.check(nonopt, opt)
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