Bug #20654: Floor and ceil have unexpected behaviour when ndigits is large

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: DONE, 3.3: DONE

[peterzhu2118 (Peter Zhu)]

GitHub PR: https://github.com/ruby/ruby/pull/11257

There is unexpected behaviour in Integer#floor, Float#floor, Integer#ceil, Float#ceil when ndigits is large such that 10**ndigits is a bignum.

Previously, it would return 0 in such cases. However, this would cause unexpected behaviour such as:

puts -1.floor(-5) # => -100000
puts -1.floor(-10) # => -10000000000
puts -1.floor(-20) # => 0

puts 1.ceil(-5) # => 100000
puts 1.ceil(-10) # => 10000000000
puts 1.ceil(-20) # => 0

The PR changes the last result so that it will return -100000000000000000000 and 100000000000000000000, respectively.

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|3af2a7fbe12e11bac7b26bd991d3d02349f47295.

---

Fix floor when ndigits is large

[Bug #20654]

This commit fixes Integer#floor and Float#floor when the number is
negative and ndigits is large such that 10**ndigits is a bignum.

Previously, it would return 0 in such cases. However, this would cause
unexpected behaviour such as:

puts -1.floor(-5) # => -100000
puts -1.floor(-10) # => -10000000000
puts -1.floor(-20) # => 0

This commit changes the last result so that it will return
-100000000000000000000.

[peterzhu2118 (Peter Zhu)]

I opened backport PRs.

3.3: https://github.com/ruby/ruby/pull/11277
3.2: https://github.com/ruby/ruby/pull/11278

[nagachika (Tomoyuki Chikanaga)]

• Backport changed from 3.1: UNKNOWN, 3.2: REQUIRED, 3.3: REQUIRED to 3.1: UNKNOWN, 3.2: DONE, 3.3: DONE

Thank you for preparing the backport PRs. They were merged.