Number of bits/sizeof int
Mark Wooding
mdw at distorted.org.uk
Mon Feb 2 20:50:33 CET 2009
Jon Clements <joncle at googlemail.com> writes:
> "The int() type gained a bit_length method that returns the number of
> bits necessary to represent its argument in binary:"
>
> Any tips on how to get this in 2.5.2 as that's the production version
> I'm stuck with.
def nbits(x):
## Special cases.
if x == 0: return 0
elif x < 0: x = -x
## Find upper bound of the form 2^(2^n) >= x.
n = 1
while True:
y = x >> n
if y == 0: break
x = y
n <<= 1
## Now binary search until we're done.
a = n
while n > 0:
n >>= 1
y = x >> n
if y > 0:
x = y
a += n
return a
-- [mdw]
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