From: "tenderlovemaking (Aaron Patterson) via ruby-core" <ruby-core@...>
Date: 2024-09-05T20:34:10+00:00
Subject: [ruby-core:119071] [Ruby master Feature#20692] Rewrite Array#bsearch in Ruby

Issue #20692 has been updated by tenderlovemaking (Aaron Patterson).


I think this is a good idea, but I think we need to make a few changes.  First, `to_enum` and `block_given?` are both method calls. It's possible for people to monkey patch Array and add those methods, but the original implementation of `Array#bsearch` would ignore such monkey patches.  To maintain existing behavior, we must use code that doesn't depend on those methods [the same way the Array#each implementation works](https://github.com/tenderlove/ruby/blob/18744851eb4e1e14be8435f77dabf3bc62bbb81d/array.rb#L47-L49).

Additionally, I think this proposal has the same problem as the initial version of the `Array#each` implementation in Ruby, specifically [a possible thread safety problem between the `<` comparison at the `[]` fetch](https://github.com/ruby/ruby/pull/6687#discussion_r1139265240).  I think we can address that by doing [the same trick as `Array#each`](https://github.com/tenderlove/ruby/blob/18744851eb4e1e14be8435f77dabf3bc62bbb81d/array.rb#L52).

----------------------------------------
Feature #20692: Rewrite Array#bsearch in Ruby
https://bugs.ruby-lang.org/issues/20692#change-109654

* Author: sebyx07 (Sebastian Buza)
* Status: Open
----------------------------------------
inspired by https://bugs.ruby-lang.org/issues/20182

# Proporsal

Rewrite Array#bsearch

```ruby
class Array
  def bsearch
    return to_enum(:bsearch) { size } unless block_given?

    return nil if empty?

    low = 0
    high = size - 1
    mid = size / 2

    case yield(self[low])
    when true, false
      while low < high
        if yield(self[mid])
          high = mid
        else
          low = mid + 1
        end
        mid = low + (high - low) / 2
      end
      yield(self[low]) ? self[low] : nil
    else
      # Find-any mode
      while low <= high
        case yield(self[mid])
        when 0
          return self[mid]
        when 1
          high = mid - 1
        when -1
          low = mid + 1
        else
          raise TypeError, 'wrong argument type (must be -1, 0, 1, true, or false)'
        end
        mid = low + (high - low) / 2
      end
      nil
    end
  end
end
```

https://github.com/sebyx07/native_ruby/blob/master/lib/native_ruby/array/bsearch.rb

I also created this gem:
https://github.com/sebyx07/native_ruby/ - to load patches w/o depending on the ruby/master

## Benchmark

```
ruby 3.3.3 (2024-06-12 revision f1c7b6f435) +YJIT [x86_64-linux]

Benchmark results sorted array (average over 10000000 iterations):
                           user     system      total        real
Original bsearch:     11.499511   0.000000  11.499511 ( 11.500056)
Native bsearch:        2.923645   0.003860   2.927505 (  2.927539)


Benchmark results shuffled (average over 10000000 iterations):
                           user     system      total        real
Original bsearch:      8.726749   0.000001   8.726750 (  8.727679)
Native bsearch:        3.073027   0.000006   3.073033 (  3.073231)
```



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