Bit

%run utils.ipynb

import_notebooks(["utils.ipynb"])

Bit#

Again, same concept but for bit operations.

Byte#

Get one byte from a word (32 bytes)

def byte(evm):
    i, x = evm.stack.pop(), evm.stack.pop()
    if i >= 32: result = 0
    else      : result = (x // pow(256, 31 - i)) % 256
    evm.stack.push(result)
    evm.pc += 1
    evm.gas_dec(3)

Bit shifts#

Let’s see what a bit shift operation looks like

bin(22) # binary of 22

'0b10110'

bin(22 << 2) # bit shift by 2 to the left

'0b1011000'

bin(22 >> 2) # bit shift by 2 to the right

'0b101'

Bit Shift left#

1010 bit shifted left by 2 positions becomes 101000

def shl(evm): 
    shift, value = evm.stack.pop(), evm.stack.pop()
    evm.stack.push(value << shift)
    evm.pc += 1
    evm.gas_dec(3)

Bit Shift right#

1010 bit shifted left by 2 positions becomes 10

def shr(evm): 
    shift, value = evm.stack.pop(), evm.stack.pop()
    evm.stack.push(value >> shift)
    evm.pc += 1
    evm.gas_dec(3)

Signed Shift right#

def sar(evm):
    shift, value = evm.stack.pop(), evm.stack.pop()
    if shift >= 256:
        result = 0 if value >= 0 else UINT_255_NEGATIVE_ONE
    else:
        result = (value >> shift) & UINT_256_MAX
        
    evm.stack.push(result)
    evm.pc += 1
    evm.gas_dec(3)
Contents