1 -> 1
5 -> 3
10 -> 4
100 -> 7
1000 -> 10
How to count bits for a number in Python?
views:
155answers:
4
+2
A:
def bitcounter(n):
return math.floor(math.log(n,2)) + 1
EDIT fixed so that it works with 1
Daniel DiPaolo
2010-04-16 15:26:10
This is off by one for powers of two.
Ants Aasma
2010-04-16 15:29:19
@Ants Aasma: Are you sure about that? It looks fine to me, assuming that math.log(n, 2) gives a perfectly correct result.
Mark Dickinson
2010-04-16 18:11:46
@Ants Aasma: it seems you think that 65536 needs 16 bits. Can you please point us to your PhD thesis? I mean, you have gold in your hands :)
ΤΖΩΤΖΙΟΥ
2010-04-16 23:13:53
+8
A:
import math
def number_of_bits(n):
return int(math.log(n, 2)) + 1
Ants Aasma
2010-04-16 15:27:38
Bear in mind that a floating-point based solution will become inaccurate for large n. Depending on how good the system's log function is, the above solution may also fail for powers of 2.2**48-1 is the smallest integer for which this fails on my system (it gives 49).
Mark Dickinson
2010-04-16 17:03:32
+5
A:
>>> len(bin(1000))-2
10
>>> len(bin(100))-2
7
>>> len(bin(10))-2
4
Note: will not work for negative numbers, may be need to substract 3 instead of 2
S.Mark
2010-04-16 15:30:38
+11
A:
In python 3 and and 2.7 there is a int.bit_length() method:
>>> a = 100
>>> a.bit_length()
7
SilentGhost
2010-04-16 15:32:07