def mulmod(evm: Evm) -> None:
"""
Modulo multiplication of the top 2 elements with the 3rd element. Pushes
the result back on the stack.
Parameters
----------
evm :
The current EVM frame.
Raises
------
StackUnderflowError
If `len(stack)` is less than `3`.
OutOfGasError
If `evm.gas_left` is less than `8`.
"""
evm.gas_left = subtract_gas(evm.gas_left, GAS_MID)
x = Uint(pop(evm.stack))
y = Uint(pop(evm.stack))
z = Uint(pop(evm.stack))
if z == 0:
result = U256(0)
else:
result = U256((x * y) % z)
push(evm.stack, result)
def div(evm: Evm) -> None:
"""
Integer division of the top two elements of the stack. Pushes the result
back on the stack.
Parameters
----------
evm :
The current EVM frame.
Raises
------
StackUnderflowError
If `len(stack)` is less than `2`.
OutOfGasError
If `evm.gas_left` is less than `5`.
"""
evm.gas_left = subtract_gas(evm.gas_left, GAS_LOW)
dividend = pop(evm.stack)
divisor = pop(evm.stack)
if divisor == 0:
quotient = U256(0)
else:
quotient = dividend // divisor
push(evm.stack, quotient)
def exp(evm: Evm) -> None:
"""
Exponential operation of the top 2 elements. Pushes the result back on
the stack.
Parameters
----------
evm :
The current EVM frame.
Raises
------
StackUnderflowError
If `len(stack)` is less than `2`.
"""
base = Uint(pop(evm.stack))
exponent = Uint(pop(evm.stack))
gas_used = GAS_EXPONENTIATION
if exponent != 0:
# This is equivalent to 1 + floor(log(y, 256)). But in python the log
# function is inaccurate leading to wrong results.
exponent_bits = exponent.bit_length()
exponent_bytes = (exponent_bits + 7) // 8
gas_used += GAS_EXPONENTIATION * exponent_bytes
evm.gas_left = subtract_gas(evm.gas_left, gas_used)
result = U256(pow(base, exponent, U256_CEIL_VALUE))
push(evm.stack, result)
def mod(evm: Evm) -> None:
"""
Modulo remainder of the top two elements of the stack. Pushes the result
back on the stack.
Parameters
----------
evm :
The current EVM frame.
Raises
------
StackUnderflowError
If `len(stack)` is less than `2`.
OutOfGasError
If `evm.gas_left` is less than `5`.
"""
evm.gas_left = subtract_gas(evm.gas_left, GAS_LOW)
x = pop(evm.stack)
y = pop(evm.stack)
if y == 0:
remainder = U256(0)
else:
remainder = x % y
push(evm.stack, remainder)
def sstore(evm: Evm) -> None:
"""
Stores a value at a certain key in the current context's storage.
Parameters
----------
evm :
The current EVM frame.
Raises
------
StackUnderflowError
If `len(stack)` is less than `2`.
OutOfGasError
If `evm.gas_left` is less than `20000`.
"""
key = pop(evm.stack).to_be_bytes32()
new_value = pop(evm.stack)
current_value = evm.env.state[evm.current].storage.get(key, U256(0))
# TODO: SSTORE gas usage hasn't been tested yet. Testing this needs
# other opcodes to be implemented.
# Calculating the gas needed for the storage
if new_value != 0 and current_value == 0:
gas_cost = GAS_STORAGE_SET
else:
gas_cost = GAS_STORAGE_UPDATE
evm.gas_left = subtract_gas(evm.gas_left, gas_cost)
# TODO: Refund counter hasn't been tested yet. Testing this needs other
# Opcodes to be implemented
if new_value == 0 and current_value != 0:
evm.refund_counter += GAS_STORAGE_CLEAR_REFUND
if new_value == 0:
# Deletes a k-v pair from dict if key is present, else does nothing
evm.env.state[evm.current].storage.pop(key, None)
else:
evm.env.state[evm.current].storage[key] = new_value
def test_u256_to_be_bytes32_max_value() -> None:
encoded = U256(2**256 - 1).to_be_bytes32()
assert encoded == bytes([
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
0xFF,
])
def test_u256_rpow_overflow() -> None:
with pytest.raises(ValueError):
(2**256)**U256(2)
def test_u256_pow_modulo_negative() -> None:
with pytest.raises(ValueError):
pow(U256(4), 2, -3)
def test_u256_pow_modulo() -> None:
value = pow(U256(4), 2, 3)
assert isinstance(value, U256)
assert value == 1
def test_u256_pow_overflow() -> None:
with pytest.raises(ValueError):
U256(340282366920938463463374607431768211456)**3
def test_u256_rdivmod_float() -> None:
quotient, remainder = divmod(5.0, U256(2))
assert not isinstance(quotient, U256)
assert not isinstance(remainder, U256)
assert quotient == 2
assert remainder == 1
def test_u256_rdivmod_overflow() -> None:
with pytest.raises(ValueError):
divmod(2**256, U256(2))
def test_u256_mod_overflow() -> None:
with pytest.raises(ValueError):
U256(5) % (2**256)
def test_u256_rmod_float() -> None:
value = (6.0) % U256(5)
assert not isinstance(value, int)
assert value == 1.0
def test_u256_rmod() -> None:
value = 6 % U256(5)
assert isinstance(value, U256)
assert value == 1
def test_u256_divmod_negative() -> None:
with pytest.raises(ValueError):
divmod(U256(5), -2)
def test_u256_divmod_float() -> None:
quotient, remainder = divmod(U256(5), 2.0)
assert not isinstance(quotient, U256)
assert not isinstance(remainder, U256)
assert quotient == 2
assert remainder == 1
def test_u256_mod_negative() -> None:
with pytest.raises(ValueError):
U256(5) % (-4)
def test_u256_rdivmod_negative() -> None:
with pytest.raises(ValueError):
divmod(-5, U256(2))
def test_u256_mod_float() -> None:
value = U256(5) % (1.0)
assert not isinstance(value, int)
assert value == 0.0
def test_u256_pow() -> None:
value = U256(3)**2
assert isinstance(value, U256)
assert value == 9
def test_u256_imod() -> None:
value = U256(5)
value %= 4
assert isinstance(value, U256)
assert value == 1
def test_u256_pow_negative() -> None:
with pytest.raises(ValueError):
U256(3)**-2
def test_u256_imod_overflow() -> None:
value = U256(5)
with pytest.raises(ValueError):
value %= 2**256
def test_u256_pow_modulo_overflow() -> None:
with pytest.raises(ValueError):
pow(U256(4), 2, 2**257)
def test_u256_imod_negative() -> None:
value = U256(5)
with pytest.raises(ValueError):
value %= -4
def test_u256_rpow() -> None:
value = 3**U256(2)
assert isinstance(value, U256)
assert value == 9
def test_u256_imod_float() -> None:
value = U256(5)
value %= 1.0 # type: ignore
assert not isinstance(value, int)
assert value == 0.0
.. contents:: Table of Contents
:backlinks: none
:local:
Introduction
------------
EVM gas constants and calculators.
"""
from ethereum.base_types import U256
from .error import OutOfGasError
GAS_VERY_LOW = U256(3)
GAS_STORAGE_SET = U256(20000)
GAS_STORAGE_UPDATE = U256(5000)
GAS_STORAGE_CLEAR_REFUND = U256(15000)
GAS_LOW = U256(5)
GAS_MID = U256(8)
GAS_EXPONENTIATION = U256(10)
def subtract_gas(gas_left: U256, amount: U256) -> U256:
"""
Subtracts `amount` from `gas_left`.
Parameters
----------
gas_left :
def test_u256_divmod_overflow() -> None:
with pytest.raises(ValueError):
divmod(U256(5), 2**256)