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| From | Mok-Kong Shen <mok-kong.shen@t-online.de> |
| Newsgroups | comp.lang.python |
| Subject | Re: Log base 2 of large integers |
| Date | Wed, 13 Aug 2014 15:46:09 +0200 |
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Am 13.08.2014 15:32, schrieb Steven D'Aprano: > Mok-Kong Shen wrote: > >> >> I like to compute log base 2 of a fairly large integer n but >> with math.log(n,2) I got: >> >> OverflowError: long int too large to convert to float. >> >> Is there any feasible work-around for that? > > If you want the integer log2, that is, the floor of log2, the simplest way > is calculate it like this: > > def log2(n): > """Return the floor of log2(n).""" > if n <= 0: raise ValueError > i = -1 > while n: > n //= 2 > i += 1 > return i > > log2(511) > => returns 8 > log2(512) > => returns 9 > log2(513) > => returns 9 > > > Does that help? That is too inaccurate (e.g. for 513 above) for me, I would like to get accuracy around 0.01 and that for very large n. M. K. Shen
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Log base 2 of large integers Mok-Kong Shen <mok-kong.shen@t-online.de> - 2014-08-13 15:05 +0200
Re: Log base 2 of large integers Skip Montanaro <skip@pobox.com> - 2014-08-13 08:16 -0500
Re: Log base 2 of large integers Mok-Kong Shen <mok-kong.shen@t-online.de> - 2014-08-13 15:50 +0200
Re: Log base 2 of large integers Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-08-13 23:32 +1000
Re: Log base 2 of large integers Mok-Kong Shen <mok-kong.shen@t-online.de> - 2014-08-13 15:46 +0200
Re: Log base 2 of large integers Marko Rauhamaa <marko@pacujo.net> - 2014-08-13 17:00 +0300
Re: Log base 2 of large integers Andrew Jaffe <a.h.jaffe@gmail.com> - 2014-08-13 15:06 +0100
Re: Log base 2 of large integers Peter Otten <__peter__@web.de> - 2014-08-13 16:17 +0200
Re: Log base 2 of large integers Peter Otten <__peter__@web.de> - 2014-08-13 15:58 +0200
Re: Log base 2 of large integers Peter Pearson <ppearson@nowhere.invalid> - 2014-08-13 16:12 +0000
Re: Log base 2 of large integers Marko Rauhamaa <marko@pacujo.net> - 2014-08-13 19:15 +0300
Re: Log base 2 of large integers Chris Angelico <rosuav@gmail.com> - 2014-08-14 02:18 +1000
Re: Log base 2 of large integers Ian Kelly <ian.g.kelly@gmail.com> - 2014-08-13 12:13 -0600
Re:Log base 2 of large integers Dave Angel <davea@davea.name> - 2014-08-13 10:10 -0400
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