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Merge pull request #11770 from ethereum/byte-equivalence

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An equivalence check for the Byte opcode
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chriseth 2021-08-10 11:04:38 +02:00 committed by GitHub
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test/formal/byte_equivalence.py Normal file
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from rule import Rule
from opcodes import *
"""
Checks that the byte opcode (implemented using shift) is equivalent to a
canonical definition of byte using extract.
"""
rule = Rule()
n_bits = 256
x = BitVec('X', n_bits)
for i in range(0, 32):
# For Byte, i = 0 corresponds to most significant bit
# But for extract i = 0 corresponds to the least significant bit
lsb = 31 - i
rule.check(
BYTE(BitVecVal(i, n_bits), x),
Concat(BitVecVal(0, n_bits - 8), Extract(8 * lsb + 7, 8 * lsb, x))
)