Bug #13928: Calling Integer.fdiv with BigDecimal returns unexpected result

• Status: Closed
• Priority: Normal
• Assignee: -
• Target version: -
• ruby -v: 2.4.2p198
• Backport: 2.2: DONTNEED, 2.3: DONTNEED, 2.4: DONE

[[e-mail] (Carl Vander)]

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:

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:

irb(main):006:0> 1.fdiv(1-BigDecimal.new("0").to_f)
=> 1.0

Using ruby 2.3.1p112, it also looks OK:

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

[nobu (Nobuyoshi Nakada)]

• Backport changed from 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN to 2.2: DONTNEED, 2.3: DONTNEED, 2.4: REQUIRED

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed

Applied in changeset trunk|r59986.

---

numeric.c: use NUM2DBL

• numeric.c (fix_fdiv_double), bignum.c (rb_big_fdiv_double): use
  NUM2DBL on unknown object. RFLOAT_VALUE is only applicable to
  T_FLOAT object. [ruby-core:82924] [Bug #13928]

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)

[nobu (Nobuyoshi Nakada)]

• Related to Bug #13986: Integer#fdiv with Complex returns unexpected value added

[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.