how to get the thighest bit position in big integers?

Aaron "Castironpi" Brady castironpi at gmail.com
Sun Oct 5 21:12:00 CEST 2008


Duncan Booth wrote:
> mmgarvey at gmx.de wrote:
> 
>> My question to the group: Does anyone know of a non-hackish way to
>> determine the required bit position in python? I know that my two
>> ideas
>> can be combined to get something working. But is there a *better* way,
>> that isn't that hackish?
>>
> How about using the hex representation of the value?
> 
> OFFSET = dict(("%x"%i, int(c)) for i,c in enumerate("5433222211111111"))
> def get_highest_bit_num(r):
> 	s = "%x"%r
> 	return len(s) * 4 - OFFSET[s[0]]
> --
> http://mail.python.org/mailman/listinfo/python-list
> 

You can replace the dict if it's faster.

OFFSET= tuple( int(x) for x in "5433222211111111" )
def get_highest_bit_num(r):
     s = "%x"%r
     return len(s) * 4 - OFFSET[int(s[0],16)]

P.S.  Back home, this sort of 'nitpicking' would be judged 
unconstructive.  Worth pointing out, or not worth saying?

P.S.S.  'Thighest' bit?  I thought the spam filters would catch that.




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