CODEWITHSUNDEEP
ruby-on-railsrubybigdecimal
Gus
Gus

Reputation: 954

rails 3.2 BigDecimal and floating point numbers comparison returns absurd result

I'm having problems working with BigDecimal in Rails 3.2.3 and ruby 1.9.3p362
the following sequence of number comparisons output absurd results

1.9.3-p362 :060 >   b = BigDecimal.new('620.56')
=> #<BigDecimal:68665e0,'0.62056E3',18(18)>

1.9.3-p362 :061 > b <= 620.56
=> false
1.9.3-p362 :062 > b > 620.56
=> true

1.9.3-p362 :063 > (b - 620.56) > 0
=> false
1.9.3-p362 :064 > (b - 620.56) == 0
=> true

in other words, this is telling that: 

B > A

and

B - A == 0

what am I missing ?

Upvotes: 1

Views: 1056

Answers (1)

zwippie
zwippie

Reputation: 15515

Welcome to the wonderful world of Floating Point Arithmetic.

This website gives a good introduction of how and why (check the Basic Answers first), but what it comes down to is:

Computer are not very accurate when it comes to floating point numbers. Rounding errors are everywhere, so you have to be careful what you do.

Upvotes: 1

Related Questions