From: Tanaka Akira <akr@...>
Date: 2013-04-06T07:34:55+09:00
Subject: [ruby-core:54037] Re: [ruby-trunk - Bug #7829] Rounding error in Ruby Time

2013/4/6 David MacMahon <davidm@astro.berkeley.edu>:

> I understand that the Float returned by Rational#to_f has limited precision and often will only approximate but not equal the value represented by the Rational.  But in the example of 57563.232824357045 we are talking about a Float value that is representable.  I think it is reasonable to expect f.to_r.to_f == f.  I think that this is possible, but it requires changing both Float#to_r and Rational#to_f and I do not have a sense of whether it is practical from a performance point of view.
>

57563.232824357045 is not representable as a Float.
f.to_r.to_f == f is true.

% ruby -e 'f = 57563.232824357045; p "%.1000g" % f, f.to_r.to_f == f'
"57563.2328243570445920340716838836669921875"
true

The actual value of the Float value is
57563.2328243570445920340716838836669921875.
-- 
Tanaka Akira