[英]Is there a function in python to get the size of an arbitrary precision number?
I'm working on a cryptographic scheme in python, so I use arbitrary precision numbers ( long
) all the time. 我正在使用python中的加密方案,所以我一直使用任意精度数字(
long
)。 I'm using python 2.7. 我正在使用python 2.7。
My problem is that I need to get the most significant two bytes (16 bits) of a number and check if they are the padding I inserted. 我的问题是我需要得到一个数字的最重要的两个字节(16位)并检查它们是否是我插入的填充。 I've tried
sys.getsizeof()
but that gives the size of the entire object and guess I could also iterate through every few bits of the number until there are only two bytes left, but is there a more pythonian way of doing this? 我已经尝试了
sys.getsizeof()
但是它给出了整个对象的大小,并猜测我还可以遍历数字的每几位,直到只剩下两个字节,但是有更多的pythonian方式吗?
Thanks in advance. 提前致谢。
This should do it for you: 这应该为你做:
>>> n = 1 << 1000
>>> n.bit_length()
1001
>>> n >> (n.bit_length() - 16)
32768L
Use long.bit_length()
. 使用
long.bit_length()
。 Eg: 例如:
% long.bit_length(1024L)
11
Or: 要么:
% 1024L.bit_length()
11
To get the first 2 bytes, assuming "first" means "least significant", use modulo 16: 要获得前2个字节,假设“first”表示“最低有效”,请使用模16:
x = 123456789
x % 2**16
52501
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