From: matz@... (Yukihiro Matsumoto)
Date: 2003-04-18T00:22:02+09:00
Subject: Re: Roundoff problem with Float and Marshal

Hi,

In message "Re: Roundoff problem with Float and Marshal"
    on 03/04/17, Rudi Cilibrasi <cilibrar@ugcs.caltech.edu> writes:

|The DBL_DIG patch makes the problem less common, but does not solve it;
|
|[[1,2,3,4], [81, 2, 118, 3146]].each { |w,x,y,z|
|a = (x.to_f + y.to_f / z.to_f) * Math.exp(w.to_f / (x.to_f + y.to_f / z.to_f))
|ma = Marshal.dump(a)
|b = Marshal.load(ma)
|if a == b
|  puts "Everything is working fine for #{a}"
|else
|  puts "PROBLEM: a is #{a}, b is #{b}, and ma is #{ma.dump}"
|end
|}
|
|Produces
|
|Everything is working fine for 3.95601527633861
|PROBLEM: a is 3.7517675036461267e+17, b is 3.7517675036461261e+17, 
|and ma is "\004\010f\e3.7517675036461267e+17"

This is caused by bad implementation of strtod that Ruby 1.8 uses (in
util.c).  I will seek for the better one.

							matz.