From: foldes.laszlo2@... Date: 2018-05-20T21:16:42+00:00 Subject: [ruby-core:87201] [Ruby trunk Bug#13754] bigdecimal with lower precision that Float Issue #13754 has been updated by karatedog (F��ldes L��szl��). That is the same problem as here: https://bugs.ruby-lang.org/issues/8826 #/ is the same method as #quo (according to documentation both methods are defined in 'bigdecimal.c' at line 1281). Currently you can divide a bigdecimal by using #/, #quo and #div but I don't really understand the design behind these methods (on a "which should do what" level). #div accepts a precision argument, while #quo does not. Without precision argument #div returns Fixnum even if its first argument is a Float, it even returns Fixnum if both divisor and dividend are Float.. Thus far I don't know any method that could be able to calculate a division AND set the proper precision on the result. What you can do is to manually set precision by using #div. If you set the precision to the same amount as the divisor, you will not miss any significant digits, the drawback is that you will see a lot of digit repetition for most of the numbers. (1019 is a long prime, its reciprocal has 1018 significant digits) ~~~ ruby > BigDecimal(1).div(1019,1019).to_s ~~~ ---------------------------------------- Bug #13754: bigdecimal with lower precision that Float https://bugs.ruby-lang.org/issues/13754#change-72190 * Author: lionel_perrin (Lionel PERRIN) * Status: Assigned * Priority: Normal * Assignee: mrkn (Kenta Murata) * Target version: * ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x64-mingw32] * Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN ---------------------------------------- Hello, I'm not sure if I've misunderstood the bigdecimal class but in the following example, I only get 12 significant digits using bigdecimal while using Float, I get a correct value with 17 significant digits. ~~~ ruby # using floats 101/0.9163472602589686 # 110.22022368622177 (OK: floating point computation) # using bigdecimal a = BigDecimal('101'); a.precs # [9, 18] b = BigDecimal('0.9163472602589686'); b.precs # [18, 27] c = a/b; c.precs # [18, 36] (OK: I understand that c is computed with 18 significant digits) c.to_s # "0.110220223686e3" (Mmm: I see only 12 significant digits) c - BigDecimal('0.110220223686e3') # 0.0 (Looks like c only stores 12 significant digits and not 18) ~~~ Using the Rational class, I've seen that the value I'm expecting is about: ~~~ ruby BigDecimal.new(Rational(101/Rational('0.9163472602589686')), 25) # 0.1102202236862217746799312e3 ~~~ -- https://bugs.ruby-lang.org/ Unsubscribe: