Arithmetic operation bug

ruby-talk
1

v1="128.015"
puts((v1.to_f*1000).to_i).to_s // giving 128014 instead of 128015

Why the the result is rounding up to 128014 but the correct result
should be 128015.

···

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2

the problem seems to be in to_i

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2009/7/24 Manoj Chourasia <manojchourasia@aol.com>

v1="128.015"
puts((v1.to_f*1000).to_i).to_s // giving 128014 instead of 128015

Why the the result is rounding up to 128014 but the correct result
should be 128015.
--
Posted via http://www.ruby-forum.com/\.

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3

I'm not an expert, but I think because when you write 128.015, the number you
actually get is 128.0149999999999863575... (because 128.015 can't be
represented as a number with a finite number of decimal digits in binary, just
like, for example, 1/17 can't be repsented with a finite decimal number in
decimal). You usually don't see this because by default only a small number of
decimal digits are shown, taking rounding into account. You can obtain a
greater number of digits using, for example, format:

puts format("%.20f", 128.015)
=> 128.01499999999998635758

Now, when you multiply the number by 1000, what you actually get is:
128014.99999999998544808477. And, since Float#to_i truncates the number (it
doesn't round it), you get the number 128014.

I hope this helps

Stefano

···

On Friday 24 July 2009, Manoj Chourasia wrote:

>v1="128.015"
>puts((v1.to_f*1000).to_i).to_s // giving 128014 instead of 128015
>
>Why the the result is rounding up to 128014 but the correct result
>should be 128015.

4

Floats are tricky:
(120..130).each{|x| puts x,((x+0.015)*1000).to_i}

Have a look at "What Every Computer Scientist Should Know About
Floating-Point Arithmetic" (http://docs.sun.com/source/806-3568/
ncg_goldberg.html)

···

On Jul 24, 9:11 am, Manoj Chourasia <manojchoura...@aol.com> wrote:

v1="128.015"
puts((v1.to_f*1000).to_i).to_s // giving 128014 instead of 128015

Why the the result is rounding up to 128014 but the correct result
should be 128015.
--
Posted viahttp://www.ruby-forum.com/.