Python left shift (sign issue)

Question

In this example I'm obtaining a positive number, but I need an expression in Python that gives the same result as in Javascript.

How can that negative result be obtained in Python?

Python 2.7

mv = 1732584193 << 5

Result:

mv = 55442694176

bin(mv) gives 0b1100111010001010010001100000001

Javascript

mv = 1732584193 << 5

Result:

mv = -391880672

mv.toString(2) gives -10111010110111001111111100000

Thanks, I've already read and tried to shift the values directly returned from that functions, with the same results. — Martin0x777, Aug 28 '12 at 16:52
Don't shift the values returned from that function. Shift, *then* apply that function. You'll also need to mask it with `0xffffffff`. — Ry-, Aug 28 '12 at 16:56

score 0 · Accepted Answer · answered Aug 28 '12 at 17:53

0

You could use ctypes to do this:

>>> import ctypes
>>> mv = ctypes.c_int32(1732584193)
>>> mv.value <<= 5
>>> mv
c_int(-391880672)
>>> bin(mv.value)
'-0b10111010110111001111111100000'

answered Aug 28 '12 at 17:53

jterrace

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Thank you jterrace. Tough already pointed to the answer, your approach is the best fit to my script. – Martin0x777 Aug 28 '12 at 18:24

Python left shift (sign issue)

1 Answers1