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Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？

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On 10/8/2012 11:13 AM, Dave Angel wrote:

>> Isn't it true, though, that Python 3.3 has a completely new
>> implementation of decimal that largely removes this disadvantage?

> I wouldn't know, I'm on 3.2.  However, I sincerely doubt if it's within
> a factor of 100 of the speed of the binary float, at least on

 >>> import timeit as tt
 >>> tt.repeat("float('1.0')-float('0.9999999999')")
[0.6856039948871151, 0.669049830953858, 0.668688006423692]
 >>> tt.repeat("Decimal('1.0')-Decimal('0.9999999999')", "from decimal 
import Decimal")
[1.3204655578092428, 1.286977575486688, 1.2893188292009938]

 >>> tt.repeat("a-b", "a = 1.0; b=0.9999999999")
[0.06100386171601713, 0.044538539999592786, 0.04451548406098027]
 >>> tt.repeat("a-b", "from decimal import Decimal as D; a = D('1.0'); b 
= D('0.9999999999')")
[0.14685526219517442, 0.12909696344064514, 0.12646059371189722]

A factor of 3, as S. Krah, the cdecimal author, claimed
-- 
Terry Jan Reedy

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Thread

To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ iMath <redstone-cold@163.com> - 2012-10-08 07:07 -0700
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Dave Angel <d@davea.name> - 2012-10-08 10:48 -0400
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Chris Angelico <rosuav@gmail.com> - 2012-10-09 02:00 +1100
    Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm � Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-09 11:39 +0000
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Dave Angel <d@davea.name> - 2012-10-08 11:13 -0400
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-10-08 16:44 +0200
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Chris Angelico <rosuav@gmail.com> - 2012-10-09 02:19 +1100
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Terry Reedy <tjreedy@udel.edu> - 2012-10-08 21:45 -0400
  Re: To get the accurate value of 1 - 0.999999999999999 ,how to implement the python algorithm ？ Dave Angel <d@davea.name> - 2012-10-08 22:20 -0400

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