Bug #8204: ObjectSpace.each_object(Bignum) can generate Bignums that are to small to be Bignums

• Status: Closed
• Assignee: ko1 (Koichi Sasada)
• Target version: 2.1.0
• ruby -v: ruby 2.1.0dev (2013-04-02 trunk 40068) [x86_64-linux]

[Hanmac (Hans Mackowiak)]

when i do:

p ObjectSpace.each_object(Bignum).to_a
=> [18446744073709551615, 3, 2394213621560389257607583714845333205]
and again:
ObjectSpace.each_object(Bignum).to_a
=> [18446744073709551615, 3, 63326588221939058800767348888534802301, 0, 0, 0]

my question: why does the 3 and the zeros show up?

n = ObjectSpace.each_object(Bignum).min #=> 0
p n.class #Bignum
p n.zero? #=> false
p n < 0 # true

okay this means i have a zero, that looks like zero, but is not a zero and its class is Bignum

(but when i try in a new ruby session)

(2**64) < 0;
p bigZero = ObjectSpace.each_object(Bignum).min #=> 0
p bigZero.class #Bignum
p bigZero.zero? #=> true

okay, this time i get a zero that looks like a zero, and react like a zero, but its still a Bignum

so where does the zeros come from and why does they react so totaly different?

[hsbt (Hiroshi SHIBATA)]

• Category set to core
• Assignee set to ko1 (Koichi Sasada)
• Target version set to 2.1.0

Note that you can obtain whichever Bignum you want using coerce. For
example:

x = (1 << 100).coerce(42).first # => 42
x.class # => Bignum

I saw that used in test/*

I never bothered to investigate it, but I'm pretty sure this could lead to
multiple bugs as MRI assumes that Bignum means big number in many places.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Closed
• % Done changed from 0 to 100

This issue was solved with changeset r40076.
Hans, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.

---

bignum.c: Bignum zero comparison

• bignum.c (rb_big_eq): test as Fixnum if possible and get rid of zero
  length Bignum. [ruby-core:53893] [Bug #8204]

[Hanmac (Hans Mackowiak)]

okay that solvs a bit, so the generated Bignums are zero too,
but for sample

ObjectSpace.each_object(Bignum).select &:zero?

still generates Bignum zeros and the 3 that was inside the Bignum list at the beginning confuses me

[nobu (Nobuyoshi Nakada)]

x = (1 << 100).coerce(42).first # => 42
x.class # => Bignum

It's a Feature.

Numeric#coerce must return a pair of converted interoperable values.

In future version, Fixnum and Bignum might be merged.
However, these commits do not intend it.
Just fixes the comparison, and hides and frees intermediate objects earlier.