From: "mame (Yusuke Endoh) via ruby-core" <ruby-core@...>
Date: 2023-06-06T05:11:42+00:00
Subject: [ruby-core:113774] [Ruby master Bug#19713] Off-by-one error when computing very large Integer numbers

Issue #19713 has been updated by mame (Yusuke Endoh).



Status changed from Open to Rejected



It is by design. `Integer#/` does integer division.



```

p 2 / 1 #=> 0

```



----------------------------------------

Bug #19713: Off-by-one error when computing very large Integer numbers

https://bugs.ruby-lang.org/issues/19713#change-103423



* Author: bannable (Joe Truba)

* Status: Rejected

* Priority: Normal

* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

----------------------------------------

Ruby computes this Elliptic Curve result incorrectly when using Integer operations, but has the correct result when using Rational:



```

a = 154476802108746166441951315019919837485664325669565431700026634898253202035277999

b = 36875131794129999827197811565225474825492979968971970996283137471637224634055579

c = 4373612677928697257861252602371390152816537558161613618621437993378423467772036

int = a / (b + c) + b / (a + c) + c / (a + b)



a = a.to_r

rational = a / (b + c) + b / (a + c) + c / (a + b)

puts [RUBY_VERSION, int == 4, rational == 4].join(' ')

```



Unfortunately, I'm not sure how to minimize this to something simpler than an EC computation.



## Actual



```

���  ~ asdf local ruby latest && ruby foo.rb

3.2.1 false true

���  ~ asdf local ruby 3.1.3 && ruby foo.rb

3.1.3 false true

���  ~

```



## Expected



```

���  ~ asdf local ruby latest && ruby foo.rb

3.2.1 true true

���  ~ asdf local ruby 3.1.3 && ruby foo.rb

3.1.3 true true

���  ~

```







-- 

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