[ruby-core:106744] [Ruby master Bug#13754] bigdecimal with lower precision that Float

Issue #13754 has been updated by mrkn (Kenta Murata).

Status changed from Assigned to Third Party's Issue

This was fixed at https://github.com/ruby/bigdecimal/issues/94.

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Bug #13754: bigdecimal with lower precision that Float
https://bugs.ruby-lang.org/issues/13754#change-95439

* Author: lionel_perrin (Lionel PERRIN)
* Status: Third Party's Issue
* Priority: Normal
* Assignee: mrkn (Kenta Murata)
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x64-mingw32]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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Hello,

I'm not sure if I've misunderstood the bigdecimal class but in the following example, I only get 12 significant digits using bigdecimal while using Float, I get a correct value with 17 significant digits.

~~~ ruby
# using floats
101/0.9163472602589686 # 110.22022368622177 (OK: floating point computation)

# using bigdecimal
a = BigDecimal('101'); a.precs # [9, 18] 
b = BigDecimal('0.9163472602589686'); b.precs # [18, 27]
c = a/b; c.precs # [18, 36]              (OK: I understand that c is computed with 18 significant digits)
c.to_s # "0.110220223686e3"              (Mmm: I see only 12 significant digits)
c - BigDecimal('0.110220223686e3') # 0.0 (Looks like c only stores 12 significant digits and not 18)
~~~

Using the Rational class, I've seen that the value I'm expecting is about: 

~~~ ruby
BigDecimal.new(Rational(101/Rational('0.9163472602589686')), 25) # 0.1102202236862217746799312e3
~~~




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