Mirror imaging binary numbers

[Grant Edwards]

On 2006-12-06, dickinsm at gmail.com <dickinsm at gmail.com> wrote:

> Yet another solution:
>
> def flipbits(x):
>     """reverse bits in a byte"""
>     x1 = x << 4 | x >> 4
>     x2 = (x1 & 51) << 2 | (x1 & 204) >> 2
>     return (x2 & 85) << 1 | (x2 & 170) >> 1
>
> The idea is to first swap the two nybbles, then swap bits 0,
> 1, 5, 6 with 2, 3, 6, 7 respectively, and finally swap bits 0,
> 2, 4, 6 with bits 1, 3, 5, 7 respectively.

It's a little less obtuse if you spell it this way:

def flipbits(x):
    """reverse bits in a byte"""
    x1 = x << 4 | x >> 4
    x2 = (x1 & 0x33) << 2 | (x1 & 0xcc) >> 2
    return (x2 & 0x55) << 1 | (x2 & 0xaa) >> 1

-- 
Grant Edwards                   grante             Yow!  Now I understand the
                                  at               meaning of "THE MOD SQUAD"!
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