ethereum.homestead.vm.instructions.keccak

Ethereum Virtual Machine (EVM) Keccak Instructions ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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

Introduction

Implementations of the EVM keccak instructions.

keccak

Pushes to the stack the Keccak-256 hash of a region of memory.

This also expands the memory, in case the memory is insufficient to access the data's memory location.

Parameters

evm : The current EVM frame.

def keccak(​evm: Evm​) -> None:
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    """
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    Pushes to the stack the Keccak-256 hash of a region of memory.
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    This also expands the memory, in case the memory is insufficient to
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    access the data's memory location.
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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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    memory_start_index = pop(evm.stack)
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    size = pop(evm.stack)
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    # GAS
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    words = ceil32(Uint(size)) // Uint(32)
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    word_gas_cost = GAS_KECCAK256_WORD * words
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    extend_memory = calculate_gas_extend_memory(
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        evm.memory, [(memory_start_index, size)]
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    )
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    charge_gas(evm, GAS_KECCAK256 + word_gas_cost + extend_memory.cost)
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    # OPERATION
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    evm.memory += b"\x00" * extend_memory.expand_by
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    data = memory_read_bytes(evm.memory, memory_start_index, size)
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    hash = keccak256(data)
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    push(evm.stack, U256.from_be_bytes(hash))
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)