Python Bitshift 32 Bit Constraint [duplicate]

Question

Possible Duplicate:
Problem in calculating checksum : casting int to signed int32

This should be a relatively easy answer, I just don't really know how to search for it...I got a few semi-relevant things, but nothing that fits what I'm trying to do.

>>> 1171855803 << 7
149997542784L # I want -326312576

In other words, treat the number as an integer and don't allow it to convert to a long. How would I do this?

I tried the solution in this question:

>>> x = 0xFFFFFFFF & (1171855803 << 7)
>>> if x > 0x7FFFFFFF: print -(~(x - 1) & 0xFFFFFFFF)
else: print x

-326312576L # yay!

It works!

Phil · Accepted Answer · 2011-08-26 07:24:19Z

1

May not be the best answer, but this works...

import numpy as np
np.int32(1171855803) << 7

answered Aug 26, 2011 at 7:24

Phil

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mirk · Accepted Answer · 2011-08-26 08:08:10Z

1

You could try

import ctypes
a=ctypes.c_int32(1171855803)
a.value<<=7
print a

which gives: c_int(-326312576)

It seems to allow platform specific bit-manipulations. I am not sure about efficiency.

answered Aug 26, 2011 at 8:08

mirk

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