Bug #17183: Float round working weirdly

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 2.7
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN

[agustincornu (Agustin Cornu)]

I encountered this issue when casting a specific float with a especific round argument.

0.5.round(15)
=> 0.5
0.5.round(16)
=> 0.5000000000000001
0.5.round(17)
=> 0.5

[agustincornu (Agustin Cornu)]

• ruby -v set to 2.7

[agustincornu (Agustin Cornu)]

This is a known issue and not a bug. My bad. I cannot delete the ticket

[marcandre (Marc-Andre Lafortune)]

• Is duplicate of Bug #14635: Float#round(n) returns a wrong result when n is big added

[marcandre (Marc-Andre Lafortune)]

• Is duplicate of deleted (Bug #14635: Float#round(n) returns a wrong result when n is big)

[marcandre (Marc-Andre Lafortune)]

• Related to Bug #14635: Float#round(n) returns a wrong result when n is big added

[marcandre (Marc-Andre Lafortune)]

I think that's a bug. Looks different but maybe related to #14365.

[shyouhei (Shyouhei Urabe)]

Agreed to @marcandre (Marc-Andre Lafortune) . This sounds like a real bug.

• Status changed from Open to Closed

Applied in changeset git|d16b68cb2204eeb5af8bd39149202b630374c67f.

---

Use Rational for Float#round with ndigits > 14

ndigits higher than 14 can result in values that are slightly too
large due to floating point limitations. Converting to rational
for the calculation and then back to float fixes these issues.

Fixes [Bug #14635]
Fixes [Bug #17183]

Co-authored by: Yusuke Endoh [e-mail]