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I am trying to do 128 bit manipulation in Python, to split the 128 bit after 32 bit

var = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF # var may take any value from 0x0 to  0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF

I have tried the 

n = 8 # for 32 bit splitting
[var[i:i+n] for i in range(0, len(var), n)]

But there is no built-in length operator to find the length for long variable. I researched bitarray module, I don't want to use bit array in my code, is there any thing in pythonic way?

Expected output would be [0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF, 0xFFFFFFFF].

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  • Do you mean [0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF,0xFFFFFFFF]? And are you declaring var with quotes? Commented Aug 17, 2015 at 14:39
  • No, I just edited my question please look into it Commented Aug 17, 2015 at 14:41
  • Can you use python3 instead of python2? Commented Aug 17, 2015 at 15:05
  • Trengo Thanks !! Good to know, I will switch to python 3 Commented Aug 17, 2015 at 15:08

2 Answers 2

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You could use bit shifting (>>) and bitwise AND (&):

In [10]: [(i >> x) & 0xFFFFFFFF for x in reversed(range(0, 128, 32))]
Out[10]: [4294967295, 4294967295, 4294967295, 4294967295]

where i is your integer. The resulting list will have 4 elements (because 128 / 32 is 4).

In your case the result is 4 equal numbers (4294967295, because 4294967295 is 0xFFFFFFFF in hex).

This works well for a known number of bits (32), but I'd rather use a helper function (following the same logic as above):

def split_bits(value, n):
    ''' Split `value` into a list of `n`-bit integers '''
    mask, parts = (1 << n) - 1, []
    parts = []
    while value:
        parts.append(value & mask)
        value >>= n
    parts.reverse()
    return parts

In action:

In [14]: split_bits(0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF, 32)
Out[14]: [4294967295, 4294967295, 4294967295, 4294967295]

In [15]: [format(i, 'X') for i in _] # show corresponding hex representations
Out[15]: ['FFFFFFFF', 'FFFFFFFF', 'FFFFFFFF', 'FFFFFFFF']

In [16]: split_bits(0b1000100110101011, 4)
Out[16]: [8, 9, 10, 11]

In [17]: [format(i, 'b') for i in _] # show corresponding binary representations
Out[17]: ['1000', '1001', '1010', '1011']
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8 Comments

Thanks a lot. is it possible to find the length of long Interger? I may need it for future, is there any possible way?
@Jonny yes, see int.bit_length.
I have already tried it, but I am puzzled its throwing this error TypeError: descriptor 'bit_length' requires a 'int' object but received a 'long'.
@Jonny hmm, what's the version of your Python interpreter?
Just throwing this out there, but splitting a negative value in this way produces an endless loop. split_bits(-1) Due to the way that Python represents numbers.
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it's better to work with numbers instead of stirng

var = 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF
[(var & (0xFFFFFFFF << 32*i)) >> (32*i) for i in range(4)]

eventually you can conver number to string hex representation

format(n, 'x')
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1 Comment

Thankew so much farincz. I have edited my problem statement please look into it

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