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headius opened this issue Oct 24, 2016 · 2 comments
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Bad to_s output for extremely small floats #4245

headius opened this issue Oct 24, 2016 · 2 comments
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core JRuby 9000 Rails
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JRuby 9.1.16.0

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@headius
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headius commented Oct 24, 2016

This is on JRuby master (pre-9.1.6.0).

[] ~/projects/rails/activesupport $ jruby -e "p 1.0e-100"
0.0

[] ~/projects/rails/activesupport $ ruby23 -e "p 1.0e-100"
1.0e-100

I confirmed the proper value does make it into the Float object, but when we to_s we're losing information.

This is used by Rails in their NumberToRoundedConverter: https://github.com/rails/rails/blob/master/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb#L63

As a result of us to_s'ing this value, we end up with a 0.0 multiplier. This breaks tests in Rails activesupport/test/number_helper_test.rb here: https://github.com/rails/rails/blob/master/activesupport/test/number_helper_test.rb#L195
@etehtsea
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I'm also seeing test_sprintf_float failure on macOS and Ubuntu Xenial:

Failure: test_sprintf_float(TestKernel)
/home/ubuntu/jruby/test/jruby/test_kernel.rb:405:in `test_sprintf_float'
     402:   # JRUBY-4802
     403:   def test_sprintf_float
     404:     assert_equal "0.00000", Kernel.sprintf("%.5f", 0.000004)
  => 405:     assert_equal "0.00001", Kernel.sprintf("%.5f", 0.000005)
     406:     assert_equal "0.00001", Kernel.sprintf("%.5f", 0.000006)
     407:   end
     408:
<"0.00001"> expected but was
<"0.00000">

@kares
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kares commented Jun 20, 2018

this is now working on 9.2 as well as 9.1.16.0 :

jruby-9.1.16.0 :010 > p 1.0e-100
1.0e-100
 => 1.0e-100

@kares kares closed this as completed Jun 20, 2018
@kares kares added this to the JRuby 9.1.16.0 milestone Jun 20, 2018
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@headius @kares @etehtsea