Why are my BigDecimal objects initialized with unexpected rounding errors?
Initialize with Strings Instead of Floats
In general, you can't get reliable behavior with Floats. You're making the mistake of initializing your BigDecimals with Float values instead of String values, which introduces some imprecision right at the beginning. For example, on my 64-bit system:
float1 = 34.13985572755337float2 = 34.13985572755338# You can use string literals here, too, if your Float can't be properly# represented. For example:## BigDecimal.new("34.13985572755337", 9)## would be safer, but Float#to_s works fine with the provided corpus.bd1 = BigDecimal.new(float1.to_s, 9)bd2 = BigDecimal.new(float2.to_s, 9)bd1.to_s#=> "0.3413985572755337E2"bd2.to_s#=> "0.3413985572755338E2"bd1.to_f == float1#=> truebd2.to_f == float2#=> trueThis is one of those cases where the internal representation of the arguments matter. Therefore, your mileage will vary depending on how you initialize your object.