"""

    Verifies a transaction.

    The gas in a transaction gets used to pay for the intrinsic cost of

    operations, therefore if there is insufficient gas then it would not

    be possible to execute a transaction and it will be declared invalid.

    Additionally, the nonce of a transaction must not equal or exceed the

    limit defined in [EIP-2681], applied retroactively.

    In practice, defining the limit as ``2**64-1`` has no impact because

    sending ``2**64-1`` transactions is improbable. It's not strictly

    impossible though, ``2**64-1`` transactions is the entire capacity of the

    Ethereum blockchain at 2022 gas limits for a little over 22 years.

    This function takes a transaction as a parameter and returns the intrinsic

    gas cost of the transaction after validation. It throws an

    `InvalidTransaction` exception if the transaction is invalid.

    [EIP-2681]: https://eips.ethereum.org/EIPS/eip-2681

    """

    intrinsic_gas = calculate_intrinsic_cost(tx)

    if intrinsic_gas > tx.gas:

        raise InvalidTransaction("Insufficient gas")

    if U256(tx.nonce) >= U256(U64.MAX_VALUE):

        raise InvalidTransaction("Nonce too high")

    return intrinsic_gas

    """

    Calculates the gas that is charged before execution is started.

    The intrinsic cost of the transaction is charged before execution has

    begun. Functions/operations in the EVM cost money to execute so this

    intrinsic cost is for the operations that need to be paid for as part of

    the transaction. Data transfer, for example, is part of this intrinsic

    cost. It costs ether to send data over the wire and that ether is

    accounted for in the intrinsic cost calculated in this function. This

    intrinsic cost must be calculated and paid for before execution in order

    for all operations to be implemented.

    The intrinsic cost includes:

    1. Base cost (`TX_BASE_COST`)

    2. Cost for data (zero and non-zero bytes)

    This function takes a transaction as a parameter and returns the intrinsic

    gas cost of the transaction.

    """

    data_cost = Uint(0)

    for byte in tx.data:

        if byte == 0:

            data_cost += TX_DATA_COST_PER_ZERO

        else:

            data_cost += TX_DATA_COST_PER_NON_ZERO

    return TX_BASE_COST + data_cost

    """

    Extracts the sender address from a transaction.

    The v, r, and s values are the three parts that make up the signature

    of a transaction. In order to recover the sender of a transaction the two

    components needed are the signature (``v``, ``r``, and ``s``) and the

    signing hash of the transaction. The sender's public key can be obtained

    with these two values and therefore the sender address can be retrieved.

    This function takes a transaction as a parameter and returns

    the address of the sender of the transaction. It raises an

    `InvalidSignatureError` if the signature values (r, s, v) are invalid.

    """

    v, r, s = tx.v, tx.r, tx.s

    if v != 27 and v != 28:

        raise InvalidSignatureError("bad v")

    if U256(0) >= r or r >= SECP256K1N:

        raise InvalidSignatureError("bad r")

    if U256(0) >= s or s >= SECP256K1N:

        raise InvalidSignatureError("bad s")

    public_key = secp256k1_recover(r, s, v - U256(27), signing_hash(tx))

    return Address(keccak256(public_key)[12:32])

    """

    Compute the hash of a transaction used in the signature.

    The values that are used to compute the signing hash set the rules for a

    transaction. For example, signing over the gas sets a limit for the

    amount of money that is allowed to be pulled out of the sender's account.

    This function takes a transaction as a parameter and returns the

    signing hash of the transaction.

    """

    return keccak256(

        rlp.encode(

            (

                tx.nonce,

                tx.gas_price,

                tx.gas,

                tx.to,

                tx.value,

                tx.data,

            )

        )

    )

    """

    Compute the hash of a transaction.

    This function takes a transaction as a parameter and returns the

    hash of the transaction.

    """

    return keccak256(rlp.encode(tx))