From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2013-01-22T18:48:50+09:00
Subject: [ruby-core:51563] [ruby-trunk - Bug #7724][Open] 6 bugs with Range#bsearch over floats


Issue #7724 has been reported by marcandre (Marc-Andre Lafortune).

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Bug #7724: 6 bugs with Range#bsearch over floats
https://bugs.ruby-lang.org/issues/7724

Author: marcandre (Marc-Andre Lafortune)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0
ruby -v: r38825


Take the following code, with from, to and search all Integer or all Float:

  (from...to).bsearch{|f| f >= search}

I expected it to:
0) never yield and return nil if range is empty, i.e. from >= to ("trivial test")
1) never yield more than 65 times for floats
   or Math.log(to-from, 2)+1 for Integer ("log test")
2) return search if from <= search < to, nil otherwise ("coverage test")
3) never yield the same `f` ("uniqueness test")
4) if range is exclusive, never yield `to` nor return `to`; if range is inclusive and block returns false always yield `to` ("end of range test")
5) never yield a number < from or > to ("out of range test")

These conditions are all respected for Integers but all can be broken for Floats
Test 0, 1, 3, 4 & 5 fail even for small ordinary float values, while test 2 requires some larger floats, say 1e100 to fail.
For example bsearch can yield over 2000 times (instead of at most 65).


These tests and a correct Ruby implementation of bsearch can be found here: https://github.com/marcandre/backports/compare/marcandre:master...marcandre:bsearch
My implementation also passes the MRI tests.


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