From: Joel VanderWerf <vjoel@...>
Date: 2006-05-18T06:26:56+09:00
Subject: Re: greatest float smaller than 1.0?

polypus wrote:
> how do i get the greatest float smaller than 1.0?
> 
> thanks
> 

Something like this maybe?

irb(main):006:0> [0.9999999999999999].pack "G"
=> "?\357\377\377\377\377\377\377"

(that was just to find out what floats look like in memory, big-endian).

irb(main):012:0> x = ("?\357" + "\377"*100).unpack "G"
=> [1.0]
irb(main):013:0> "%30f" % x
=> "0.999999999999999888977697537484"

Dunno if that's safe on all platforms...

Incidentally, something is wrong with Float::EPSILON, which Mauricio
suggested and should (AFAIK) work:

irb(main):016:0* f = (1.0 - Float::EPSILON)
=> 1.0
irb(main):017:0> "%.20f" % f
=> "0.99999999999999977796"
irb(main):019:0> x[0]-f
=> 1.11022302462516e-16

Whaa???

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407