[ruby-list:35956] Float#to_r (Re: 9.2 及醒襖互 9.199999999999999)

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箔沓 懇抸匹允﹝

At Tue, 17 Sep 2002 15:07:11 +0900,
<rubyist / mh1.117.ne.jp> wrote:
> 9.2及醒襖毛醫じ仄﹜今六月午9.199999999999999卞卅曰引仄凶﹝
> 仇木勻化﹜酷杅互拑中仇午匹仄斤丹井〝

At Tue, 17 Sep 2002 15:55:45 +0900
<f-hiro / eweb.co.jp> wrote:
> ﹛迕籣卞手方月午反閤中引允互﹜簧蘸毛拑骰允木壬Ruby分午Bignum互銀尹月及匹﹜
> 忏⑹凝醒及醫歹曰卞必正毛反井六凶醒襖匹梢遙允月午中丹及反升丹匹仄斤丹井〝

9.2 仁日中及擎蘸匹中中及卅日壬﹜(井勾簧蘸毛拑骰匹五木壬)
require "rational"
Rational(92,10)
午健尹壬中中井午閤中引允﹝

require "mathn"
手墊卅丹午﹜92/10 匹碧戈及匹﹜棵簽卞惜④中中咫漶阬


う櫆毛优邰卅擎蘸匹 Rational 卞庍晶允月凶戶及憤綜仿奶皮仿伉 ---
填蟲讀卞反 Float class 卞 .to_r(precP (prec反擎蘸) 丟玉毛
勾仃笛尹月 --- 毛驕尥仄化心引仄凶﹝

箔沓 懇抸

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# fl2rat.rb
class Float
  def to_r(precP
    ## Do "include Math" and "require 'rational'" first.

    case self
    when Integer, Rational, 0
      return self.to_r
    end

    if self < 0
      keta**(log10(-self).floor)
    else
      keta**(log10(self).floor)
    end

    keta2**(prec-1)
    (keta.to_r)*((self/keta)*keta2).round/keta2
  end
end

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irb(main):001:0> require  'rational'
true
irb(main):002:0> include Math
Object
irb(main):003:0> require "fl2rat"
true
irb(main):004:0> 9.2.to_r
Rational(46, 5)
irb(main):005:0> 99.999.to_r
Rational(99999, 1000)
irb(main):006:0> 99.9999.to_r
Rational(100, 1)
irb(main):007:0> 99.9999.to_r(6)
Rational(999999, 10000)
irb(main):008:0> -99.9999.to_r(6)
Rational(-999999, 10000)
irb(main):009:0> 9.2e-10.to_r
Rational(23, 25000000000)
irb(main):011:0> 23.0/25000000000
9.2e-10
irb(main):012:0> 

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