问题
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!
回答1:
May not be the best answer, but this works...
import numpy as np
np.int32(1171855803) << 7
回答2:
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.
来源：https://stackoverflow.com/questions/7201207/python-bitshift-32-bit-constraint