Issue #13928 has been updated by nagachika (Tomoyuki Chikanaga).

Backport changed from 2.2: DONTNEED, 2.3: DONTNEED, 2.4: REQUIRED to 2.2: DONTNEED, 2.3: DONTNEED, 2.4: DONE

ruby_2_4 r62171 merged revision(s) 59986.

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Bug #13928: Calling Integer.fdiv with BigDecimal returns unexpected result
https://bugs.ruby-lang.org/issues/13928#change-70138

* Author: calle.vander / gmail.com (Carl Vander)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.4.2p198
* Backport: 2.2: DONTNEED, 2.3: DONTNEED, 2.4: DONE
----------------------------------------
After upgrading a Rails project from 2.3.1 to 2.4.2 I ran into a number of failing tests. Seems like to behaviour of fdiv and conjuction with bigdecimal is wrong.

### Reproduce by running:
```ruby
irb(main):001:0> require 'bigdecimal'
=> true
irb(main):002:0> 1.fdiv(1-BigDecimal.new("0"))
=> 2.1296133346e-314
```
Ruby version: ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16]

### I would expect the calculation to return 1, which is correctly done if converting the big decimal to a float first:
```ruby
irb(main):006:0> 1.fdiv(1-BigDecimal.new("0").to_f)
=> 1.0
```

### Using ruby 2.3.1p112, it also looks OK:
```ruby
irb(main):001:0> require 'bigdecimal'
=> true
irb(main):002:0> 1.fdiv(1-BigDecimal.new("0"))
=> #<BigDecimal:7fb6b8949690,'0.1E1',9(36)>
irb(main):003:0> 1.fdiv(1-BigDecimal.new("0")).to_i
=> 1





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