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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 Tue, Oct 9, 2012 at 2:13 AM, Dave Angel <d@davea.name> wrote:
> On 10/08/2012 11:00 AM, Chris Angelico wrote:
>> On Tue, Oct 9, 2012 at 1:48 AM, Dave Angel <d@davea.name> wrote:
>>> The Decimal class has the disadvantage that it's tons slower on any modern machine I know of...
>> Isn't it true, though, that Python 3.3 has a completely new
>> implementation of decimal that largely removes this disadvantage?
>>
>> ChrisA
>
> 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
> pentium-class machines that do binary float in microcode. A dozen years
> or so ago, when the IEEE floating point standard was still being formed,
> I tried to argue the committee into including decimal in the standard
> (which they did much later).  Had it been in the standard then, we MIGHT
> have had decimal fp on chip as well as binary.  Then again, the standard
> was roughly based on the already-existing Intel 8087, so maybe it was
> just hopeless.
>
> I guess it's possible that for some operations, the cost of the
> byte-code interpreter and function lookup, etc. might reduce the
> apparent penalty.  Has anybody done any timings?

Try this, from python-dev list:

http://mail.python.org/pipermail/python-dev/2012-September/121832.html

It's not as fast as float, but it sure gives a good account for itself.

ChrisA

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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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