2000-1992.2 - is this a known bug?


#1

ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]

2000-1992.2
=> 7.79999999999995


#2

2009/3/6 S2 removed_email_address@domain.invalid:

ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]

2000-1992.2
=> 7.79999999999995

http://docs.sun.com/source/806-3568/ncg_goldberg.html


#3

2000-1992.2
=> 7.79999999999995

It is known non-bug:
http://docs.sun.com/source/806-3568/ncg_goldberg.html

Regards,
Rimantas


#4

2009/3/6 S2 removed_email_address@domain.invalid:

ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]

2000-1992.2
=> 7.79999999999995

The use of inexact floating point numbers by default in Ruby (which
follows C and most, but not all, other programming languages) is a
design choice, not a bug. One might dispute whether or not its a good
design choice (personally, I prefer Scheme’s numeric tower and exact
numbers by default with conversion to inexact numbers only when an
inexact operation is applied to an exact number or an explicit
designation of an inexact number is given), but its a point about
which people could debate endlessly, and since BigDecimal is at least
in the standard library, its not a matter of whether Ruby can do exact
math, but just how verbose the code is to do it.

ex:

require ‘bigdecimal’
require ‘bigdecimal/math’

class BigDecimal

BigDecimal.to_s is ugly

def pretty
digits, magnitude = to_s.split(’.’)[1].split(‘E’)
magnitude=magnitude.to_i
digits.insert(0,‘0’*[(1-magnitude),0].max)
digits.insert([magnitude,1].min,’.’)
end
end

include BigMath

(2000-BigDecimal(‘1992.2’)).pretty
=> “7.8”


#5

On Fri, Mar 6, 2009 at 7:42 PM, Christopher D. removed_email_address@domain.invalid
wrote:

design choice, not a bug. One might dispute whether or not its a good
require ‘bigdecimal’
end

include BigMath

(2000-BigDecimal(‘1992.2’)).pretty
=> “7.8”

Or, while that works for the case presented, if you want it to work
right in general:

class BigDecimal
def pretty
return to_i.to_s if self==to_i
digits, magnitude = to_s.split(’.’)[1].split(‘E’)
magnitude = magnitude.to_i
digits.insert(0,‘0’*[(1-magnitude),0].max)
digits.insert([magnitude, 1].max,’.’)
end
end


#6

Hi,

2009/3/7 Christopher D. removed_email_address@domain.invalid:

design choice, not a bug. One might dispute whether or not its a good
require ‘bigdecimal’
end

include BigMath

(2000-BigDecimal(‘1992.2’)).pretty
=> “7.8”

Why not use BigDecimal.to_s(‘F’) ?

Refer to
http://www.ruby-doc.org/stdlib/libdoc/bigdecimal/rdoc/classes/BigDecimal.html#M000032

Regards,

Park H.


#7

On Fri, Mar 6, 2009 at 8:15 PM, Heesob P. removed_email_address@domain.invalid wrote:

  digits.insert(0,‘0’*[(1-magnitude),0].max)

Refer to http://www.ruby-doc.org/stdlib/libdoc/bigdecimal/rdoc/classes/BigDecimal.html#M000032

Because that would be sane?

No, seriouly, I knew there was a BigDecimal formatter somewhere that
I’d seen (and even used, though not recently), but I thought it was
external. Clearly, it’s better to use that than to try to reinvent the
wheel.