Ruby

Feature #21650

Updated by koilanetroc (Oleg Tolmashov) about 24 hours ago

## Summary 
 `Rational#floor(ndigits)` with a very large positive ndigits takes tens of seconds in Ruby 3.4, while it returns essentially instantly in Ruby 3.2. Reproducible on macOS and Linux. Looks like a missing fast‑path for rationals whose decimal expansion terminates. 

 ## Steps to reproduce 
 ```ruby 
 require "benchmark" 

 puts RUBY_DESCRIPTION 
 t = Benchmark.realtime { (2 ** -3).floor(2 ** 31) } 
 puts "elapsed: #{t.round(3)}s" 
 ``` 

 Also reproduces with the explicit rational form: 
 ```ruby 
 Benchmark.realtime { Rational(1, 8).floor(2 ** 31) } 
 ``` 

 ### Results on my machine 
 Ruby 3.2.8: 
 ``` 
 ruby 3.2.8 (2025-03-26 revision 13f495dc2c) [arm64-darwin24] 
 slow_math.rb:4: warning: in a**b, b may be too big 
 elapsed: 0.0s 
 ``` 

 Ruby 3.4.7: 
 ``` 
 ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin24] 
 elapsed: 39.214s 
 ``` 
 ## Actual behavior 
 On Ruby 3.4.x this call takes ~tens of seconds (e.g., ~40s on my machine), consuming CPU. Same on macOS and Linux. 

 ## Expected behavior 
 The method should return quickly ышьшдфкдн фы (ideally O(1)).

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