Rotate array using python as one block binary

Question

I have one array like [4, 255, 16], with dtype = int8. I want to rotate it left but like a binary rotate.

I want my array to be as explained below:

000001001111111100010000

After rotate left 2 bits, it will be:

000100111111110001000000

In decimal like [17, 252, 64]

Did you try anything already? It is always better when we have some code as starting point. — Netwave
– Netwave, Commented Mar 25, 2019 at 12:52

han solo · Accepted Answer · 2019-03-25 13:05:36Z

3

You can use deque from collections if you want to rotate it nicely,

>>> from array import array
>>> from collections import deque
>>> x = array('l', [4, 255, 16])
>>> x
array('l', [4, 255, 16])
>>> z = ''.join([format(y, 'b').zfill(8) for y in x.tolist()])
>>> z
'000001001111111100010000'
>>> d = deque(z)
>>> d.rotate(-2)
>>> ''.join(d)
'000100111111110001000000'
>>> k = ''.join(d)
>>> [int(k[i:i+8],2) for i in range(0, len(k), 8)]
[19, 252, 64]

answered Mar 25, 2019 at 13:05

han solo

6,6401 gold badge20 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

David Buck Over a year ago

Why use array? z = ''.join([format(y, 'b').zfill(8) for y in x]) if x= [4, 255, 16] works just fine.

han solo Over a year ago

@DavidBuck I just wanted to show the user, if he already has an array. And the question, started with, I have one array like [4, 255, 16], with dtype = int8. Which is array.array('l', [4, 255, 16]) :)

Grijesh Chauhan Over a year ago

Thanks for the interesting answers. Though, can be remove .tolist() ?

han solo Over a year ago

@GrijeshChauhan Sure, he could have just started with a simple list

Olivier Melançon · Accepted Answer · 2019-03-25 15:42:27Z

You want to rotate the array as if it were one long integer.

The solution below converts the array into one long integer, that is simply a Python int, rotates it with bitwise arithmetic, then write it back in the array.

Code

from array import array

def shift_left(arr, shift=1):
    if not arr:
        return

    long = 0
    itemsize = arr.itemsize * 8
    bit_length = len(arr) * itemsize
    item_bits = (1 << itemsize) - 1
    bits = (1 << bit_length) - 1

    # Convert the array to a long integer
    for i, x in enumerate(reversed(arr)):
        long |= x << (i * itemsize)

    # Left part of the | shifts the long left and drops the overflow
    # Right part of the | adds the last bits at the start of the long
    long = (long << shift & bits) | long >> (bit_length - shift)

    # Write back the long integer in the array
    for i in range(1, len(arr) + 1):
        arr[-i] = long & item_bits
        long >>= itemsize

Example

arr = array('B', [4, 255, 16])
shift_left(arr, shift=2)
print(arr)

Output

array('B', [19, 252, 64])

Collectives™ on Stack Overflow

Rotate array using python as one block binary

2 Answers 2

4 Comments

Code

Example

Output

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Code

Example

Output

Comments

Your Answer

Sign up or log in

Post as a guest

Related