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Groups > comp.lang.python > #81100
| From | Serhiy Storchaka <storchaka@gmail.com> |
|---|---|
| Subject | Re: Challenge: optimizing isqrt |
| Date | 2014-11-20 20:00 +0200 |
| References | <54543787$0$13005$c3e8da3$5496439d@news.astraweb.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.16037.1416506494.18130.python-list@python.org> (permalink) |
On 01.11.14 03:29, Steven D'Aprano wrote:
> There is an algorithm for calculating the integer square root of any
> positive integer using only integer operations:
Here is my optimized implementation inspired by Christian's ideas.
import math, sys
C1 = sys.float_info.radix ** sys.float_info.mant_dig
C2 = int(sys.float_info.max)
C3 = C2.bit_length() - 2
def isqrt(n):
if n < 0:
raise ValueError
if n == 0:
return 0
if n <= C1:
return int(math.sqrt(n))
if n <= C2:
x = int(math.sqrt(n))
else:
b = (n.bit_length() - C3) // 2
x = int(math.sqrt(n >> (2 * b))) << b
y = (x + n // x) // 2
if y == x:
return x
while True:
x = y
y = (x + n // x) // 2
if y >= x:
return x
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Challenge: optimizing isqrt Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 12:29 +1100
Re: Challenge: optimizing isqrt Chris Angelico <rosuav@gmail.com> - 2014-11-01 13:12 +1100
Re: Challenge: optimizing isqrt Christian Gollwitzer <auriocus@gmx.de> - 2014-11-01 09:02 +0100
Re: Challenge: optimizing isqrt Christian Gollwitzer <auriocus@gmx.de> - 2014-11-01 09:09 +0100
Re: Challenge: optimizing isqrt Chris Angelico <rosuav@gmail.com> - 2014-11-01 19:13 +1100
Re: Challenge: optimizing isqrt Christian Gollwitzer <auriocus@gmx.de> - 2014-11-01 09:25 +0100
Re: Challenge: optimizing isqrt Chris Angelico <rosuav@gmail.com> - 2014-11-01 19:33 +1100
Re: Challenge: optimizing isqrt Christian Gollwitzer <auriocus@gmx.de> - 2014-11-01 09:38 +0100
Re: Challenge: optimizing isqrt Chris Angelico <rosuav@gmail.com> - 2014-11-01 19:45 +1100
Re: Challenge: optimizing isqrt Akira Li <4kir4.1i@gmail.com> - 2014-11-01 12:12 +0300
Re: Challenge: optimizing isqrt Serhiy Storchaka <storchaka@gmail.com> - 2014-11-20 20:00 +0200
Re: Challenge: optimizing isqrt Stephen Tucker <stephen_tucker@sil.org> - 2014-11-21 08:15 +0000
Re: Challenge: optimizing isqrt Dave Angel <davea@davea.name> - 2014-11-23 10:43 -0500
Re: Challenge: optimizing isqrt Serhiy Storchaka <storchaka@gmail.com> - 2014-11-25 21:31 +0200
Re: Challenge: optimizing isqrt Dave Angel <davea@davea.name> - 2014-11-25 19:46 -0500
Re: Challenge: optimizing isqrt Stephen Tucker <stephen_tucker@sil.org> - 2014-11-26 07:57 +0000
Re: Challenge: optimizing isqrt Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-26 21:25 +1100
Re: Challenge: optimizing isqrt Serhiy Storchaka <storchaka@gmail.com> - 2014-11-26 18:24 +0200
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