ethereum.forks.prague.vm.instructions.memory

Ethereum Virtual Machine (EVM) Memory Instructions.

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Implementations of the EVM Memory instructions.

mstore

Stores a word to memory. This also expands the memory, if the memory is insufficient to store the word.

Parameters

evm : The current EVM frame.

def mstore(​evm: Evm​) -> None:
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    """
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    Stores a word to memory.
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    This also expands the memory, if the memory is
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    insufficient to store the word.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    start_position = pop(evm.stack)
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    value = pop(evm.stack).to_be_bytes32()
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    # GAS
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    extend_memory = calculate_gas_extend_memory(
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        evm.memory, [(start_position, U256(len(value)))]
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    )
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    charge_gas(evm, GasCosts.OPCODE_MSTORE_BASE + extend_memory.cost)
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    # OPERATION
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    evm.memory += b"\x00" * extend_memory.expand_by
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    memory_write(evm.memory, start_position, value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

mstore8

Stores a byte to memory. This also expands the memory, if the memory is insufficient to store the word.

Parameters

evm : The current EVM frame.

def mstore8(​evm: Evm​) -> None:
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    """
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    Stores a byte to memory.
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    This also expands the memory, if the memory is
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    insufficient to store the word.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    start_position = pop(evm.stack)
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    value = pop(evm.stack)
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    # GAS
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    extend_memory = calculate_gas_extend_memory(
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        evm.memory, [(start_position, U256(1))]
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    )
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    charge_gas(evm, GasCosts.OPCODE_MSTORE8_BASE + extend_memory.cost)
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    # OPERATION
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    evm.memory += b"\x00" * extend_memory.expand_by
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    normalized_bytes_value = Bytes([value & U256(0xFF)])
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    memory_write(evm.memory, start_position, normalized_bytes_value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

mload

Loads a word from memory.

Parameters

evm : The current EVM frame.

def mload(​evm: Evm​) -> None:
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    """
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    Loads a word from memory.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    start_position = pop(evm.stack)
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    # GAS
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    extend_memory = calculate_gas_extend_memory(
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        evm.memory, [(start_position, U256(32))]
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    )
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    charge_gas(evm, GasCosts.OPCODE_MLOAD_BASE + extend_memory.cost)
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    # OPERATION
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    evm.memory += b"\x00" * extend_memory.expand_by
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    value = U256.from_be_bytes(
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        memory_read_bytes(evm.memory, start_position, U256(32))
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    )
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    push(evm.stack, value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

msize

Pushes the size of active memory in bytes onto the stack.

Parameters

evm : The current EVM frame.

def msize(​evm: Evm​) -> None:
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    """
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    Pushes the size of active memory in bytes onto the stack.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    pass
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_MSIZE)
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    # OPERATION
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    push(evm.stack, U256(len(evm.memory)))
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

mcopy

Copies the bytes in memory from one location to another.

Parameters

evm : The current EVM frame.

def mcopy(​evm: Evm​) -> None:
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    """
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    Copies the bytes in memory from one location to another.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    # STACK
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    destination = pop(evm.stack)
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    source = pop(evm.stack)
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    length = pop(evm.stack)
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    # GAS
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    words = ceil32(Uint(length)) // Uint(32)
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    copy_gas_cost = GasCosts.OPCODE_COPY_PER_WORD * words
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    extend_memory = calculate_gas_extend_memory(
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        evm.memory, [(source, length), (destination, length)]
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    )
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    charge_gas(
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        evm,
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        GasCosts.OPCODE_MCOPY_BASE + copy_gas_cost + extend_memory.cost,
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    )
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    # OPERATION
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    evm.memory += b"\x00" * extend_memory.expand_by
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    value = memory_read_bytes(evm.memory, source, length)
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    memory_write(evm.memory, destination, value)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)