ethereum.forks.bpo1.vm.instructions.bitwiseethereum.forks.bpo2.vm.instructions.bitwise

Ethereum Virtual Machine (EVM) Bitwise Instructions.

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

Introduction

Implementations of the EVM bitwise instructions.

bitwise_and

Bitwise AND operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_and(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    x = pop(evm.stack)
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    y = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_AND)
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    # OPERATION
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    push(evm.stack, x & y)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_or

Bitwise OR operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_or(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    x = pop(evm.stack)
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    y = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_OR)
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    # OPERATION
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    push(evm.stack, x | y)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_xor

Bitwise XOR operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_xor(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    x = pop(evm.stack)
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    y = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_XOR)
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    # OPERATION
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    push(evm.stack, x ^ y)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_not

Bitwise NOT operation of the top element of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_not(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    x = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_NOT)
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    # OPERATION
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    push(evm.stack, ~x)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

get_byte

For a word (defined by next top element of the stack), retrieve the Nth byte (0-indexed and defined by top element of stack) from the left (most significant) to right (least significant).

Parameters

evm : The current EVM frame.

def get_byte(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    byte_index = pop(evm.stack)
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    word = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_BYTE)
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    # OPERATION
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    if byte_index >= U256(32):
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        result = U256(0)
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    else:
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        extra_bytes_to_right = U256(31) - byte_index
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        # Remove the extra bytes in the right
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        word = word >> (extra_bytes_to_right * U256(8))
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        # Remove the extra bytes in the left
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        word = word & U256(0xFF)
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        result = word
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    push(evm.stack, result)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_shl

Logical shift left (SHL) operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_shl(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    shift = Uint(pop(evm.stack))
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    value = Uint(pop(evm.stack))
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_SHL)
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    # OPERATION
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    if shift < Uint(256):
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        result = U256((value << shift) & Uint(U256.MAX_VALUE))
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    else:
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        result = U256(0)
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    push(evm.stack, result)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_shr

Logical shift right (SHR) operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_shr(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    shift = pop(evm.stack)
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    value = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_SHR)
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    # OPERATION
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    if shift < U256(256):
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        result = value >> shift
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    else:
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        result = U256(0)
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    push(evm.stack, result)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

bitwise_sar

Arithmetic shift right (SAR) operation of the top 2 elements of the stack. Pushes the result back on the stack.

Parameters

evm : The current EVM frame.

def bitwise_sar(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    shift = int(pop(evm.stack))
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    signed_value = pop(evm.stack).to_signed()
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_SAR)
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    # OPERATION
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    if shift < 256:
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        result = U256.from_signed(signed_value >> shift)
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    elif signed_value >= 0:
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        result = U256(0)
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    else:
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        result = U256.MAX_VALUE
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    push(evm.stack, result)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)

count_leading_zeros

Count the number of leading zero bits in a 256-bit word.

Pops one value from the stack and pushes the number of leading zero bits. If the input is zero, pushes 256.

Parameters

evm : The current EVM frame.

def count_leading_zeros(​evm: Evm​) -> None:
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    <snip>
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    # STACK
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    x = pop(evm.stack)
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    # GAS
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    charge_gas(evm, GasCosts.OPCODE_CLZ)
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    # OPERATION
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    bit_length = U256(x.bit_length())
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    result = U256(256) - bit_length
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    push(evm.stack, result)
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    # PROGRAM COUNTER
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    evm.pc += Uint(1)