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Re: IE and IEE 754

From Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups comp.lang.javascript
Subject Re: IE and IEE 754
Date 2014-08-29 20:42 +0100
Organization A noiseless patient Spider
Message-ID <87mwangjzy.fsf@bsb.me.uk> (permalink)
References (4 earlier) <ltlum5$k04$1@solani.org> <87sikgzz71.fsf@bsb.me.uk> <3souv99slp2vt6nktr48gadd2e4r8th8o4@4ax.com> <871ts0md0v.fsf@bsb.me.uk> <cog10a1blbhp80gnvsj0tadeb4glh343jt@4ax.com>

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Gene Wirchenko <genew@telus.net> writes:

> On Fri, 29 Aug 2014 00:04:48 +0100, Ben Bacarisse
> <ben.usenet@bsb.me.uk> wrote:
>
>>Gene Wirchenko <genew@telus.net> writes:
>>
>>> On Thu, 28 Aug 2014 11:27:30 +0100, Ben Bacarisse
>>> <ben.usenet@bsb.me.uk> wrote:
>>>
>>> [snip]
>>>
>>>>I think it must.  The ECMAScript specification imports IEEE 754's strict
>>>>rounding and representation rules.  The IEEE FP value closest to 123.45,
>>>>when multiplies by 100 must yield 12345 according to those rules.
>>>
>>>      Why?  What if the value that you have (and want) happens to be
>>> the value closest to 123.45?  When you multiply that value by 100,
>>> wouldn't you want 100 times the value instead of 12345?
>>
>>Yes, but you won't get it.  You'll get the nearest floating point
>>number, which is 12345.  Am I missing your point?
>
>      Yes.  The value closest to 123.45 can be represented exactly.

Sure.  To be specific, for IEEE 754 double, it's 7B.733333333334 in hex.
Using enough decimal digits to see what happening, that's about

  123.45000000000000284217...

> So can 100 times that value.

That's an odd idea.  Why do you think it might be?

> That value is not 12345.

Yup, it's

  12345.000000000000284217...

> That 100 times value would be what is wanted, not 12345.

It's what you want, but, as I said, what you'll get is the nearest
representable floating point number.  The three candidates are centred
on 12345:

  12344.999999999998181011...
  12345.000000000000000000...
  12345.000000000001818989...

and 12345.0 is the closest.  (Assuming I have not made some blunder with
the arithmetic -- please check it.)

I'm still not sure I've got your point, but you've said what appears to
be the same thing twice now, so I don't know what else to say.

-- 
Ben.

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IE and IEE 754 RobG <rgqld@iinet.net.au> - 2014-08-27 22:44 +1000
  Re: IE and IEEE 754 John Harris <niam@jghnorth.org.uk.invalid> - 2014-08-27 15:23 +0100
  IE and IEEE 754 (was: IE and IEE 754) Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-27 20:59 +0200
  Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-27 22:04 +0200
    Re: IE and IEE 754 "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-27 22:35 +0200
      Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 00:07 +0200
        Re: IE and IEE 754 "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-28 00:47 +0200
          Re: IE and IEE 754 Gene Wirchenko <genew@telus.net> - 2014-08-28 10:13 -0700
            Re: IE and IEE 754 "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-28 22:15 +0200
              Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 23:24 +0200
                Re: IE and IEE 754 "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-29 01:16 +0200
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-29 09:32 +0200
      Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-27 23:59 +0100
        Re: IE and IEE 754 "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-28 02:55 +0200
          Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 09:50 +0200
            Re: IE and IEE 754 Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-28 12:21 +0200
              Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 13:42 +0200
          Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-28 11:27 +0100
            Re: IE and IEE 754 Gene Wirchenko <genew@telus.net> - 2014-08-28 10:16 -0700
              Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 00:04 +0100
                Re: IE and IEE 754 Gene Wirchenko <genew@telus.net> - 2014-08-29 11:15 -0700
                IEEE 754 (was: IE and IEE 754) "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-29 21:30 +0200
                Re: IEEE 754 (was: IE and IEE 754) Gene Wirchenko <genew@telus.net> - 2014-09-02 11:22 -0700
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 20:42 +0100
                IEEE 754 (was: IE and IEE 754) "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-29 23:29 +0200
                Re: IEEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 23:27 +0100
                Re: IE and IEE 754 Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-08-30 20:32 +0100
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-31 01:04 +0100
                IE and IEEE 754 Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-09-01 23:05 +0100
    Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-28 00:05 +0100
      Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 08:56 +0200
        Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 09:51 +0200
          Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-28 11:16 +0100
            Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-28 13:34 +0200
              Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-28 23:41 +0100
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-29 09:09 +0200
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 12:39 +0100
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-29 16:55 +0200
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 18:28 +0100
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 00:37 +0200
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-29 23:53 +0100
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 01:08 +0200
                Re: IE and IEE 754 Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-08-30 00:40 +0100
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 09:32 +0200
                Re: IE and IEE 754 Gene Wirchenko <genew@telus.net> - 2014-08-29 11:22 -0700
                Re: IE and IEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 00:14 +0200
  IE and IEEE 754 (was: IE and IEE 754) "Christoph M. Becker" <cmbecker69@arcor.de> - 2014-08-27 22:08 +0200
    Re: IE and IEEE 754 RobG <rgqld@iinet.net.au> - 2014-08-28 22:50 +1000
    Re: IE and IEEE 754 RobG <rgqld@iinet.net.au> - 2014-08-28 22:55 +1000
    Re: IE and IEEE 754 (was: IE and IEE 754) Dr J R Stockton <reply1400@merlyn.demon.co.uk.invalid> - 2014-08-28 21:50 +0100
      Re: IE and IEEE 754 (was: IE and IEE 754) "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-29 09:43 +0200
        Re: IE and IEEE 754 (was: IE and IEE 754) Denis McMahon <denismfmcmahon@gmail.com> - 2014-08-29 08:42 +0000
        Re: IE and IEEE 754 Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-30 16:24 +0200
          Re: IE and IEEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 17:08 +0200
            Re: IE and IEEE 754 Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2014-08-30 18:12 +0200
              Re: IE and IEEE 754 "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2014-08-30 18:32 +0200

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