如何修改整数位？

Question

我有一个带值7(0b00000111)的整数我想用函数替换它13(0b00001101).替换整数位的最佳算法是什么？

例如:

set_bits(somevalue, 3, 1) # What makes the 3rd bit to 1 in somevalue?

Answer 1

您只需要:

def set_bit(v, index, x):
  """Set the index:th bit of v to 1 if x is truthy, else to 0, and return the new value."""
  mask = 1 << index   # Compute mask, an integer with just bit 'index' set.
  v &= ~mask          # Clear the bit indicated by the mask (if x is False)
  if x:
    v |= mask         # If x was True, set the bit indicated by the mask.
  return v            # Return the result, we're done.

>>> set_bit(7, 3, 1)
15
>>> set_bit(set_bit(7, 1, 0), 3, 1)
13

注意,位数(index)从0开始,0是最低有效位.

还要注意,返回了新值,没有办法像你显示的那样"就地"修改整数(至少我不这么认为).

Answer 2

这些适用于任何大小的整数,甚至大于32位:

def set_bit(value, bit):
    return value | (1<<bit)

def clear_bit(value, bit):
    return value & ~(1<<bit)

如果你喜欢简短的东西,你可以使用:

>>> val = 0b111
>>> val |= (1<<3)
>>> '{:b}'.format(val)
'1111'
>>> val &=~ (1<<1)
'1101'

Answer 3

您可以使用按位运算. http://wiki.python.org/moin/BitwiseOperators

如果要将给定位设置为1,则可以在给定位置使用按位"或"1:

0b00000111 | 0b00001000 = 0b00001111

要将给定位设置为0,您可以使用按位'和'

0b00001111和0b11111011 = 0b00001011

请注意,0b前缀用于二进制数,0x用于十六进制数.