Issue #22246 has been updated by nobu (Nobuyoshi Nakada). ```console $ ruby -e 'x = 65803600513127829623; [65803600.51312783, 65803600.513127826].each {|n| p ((n*10**12).to_i-x).abs}' 3977 4215 ``` Isn't the current result closer? ---------------------------------------- Bug #22246: Rational#to_f incorrectly rounds when the numerator is a bignum that cannot be represented exactly by a double, and the denominator is a fixnum https://bugs.ruby-lang.org/issues/22246#change-118603 * Author: AndrewDile (Andrew Dile) * Status: Open * ruby -v: 4.0.6 * Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN ---------------------------------------- ``` c Rational(65803600513127829623, 10**12).to_f ``` The bignum numerator cannot be exactly represented by a double, but the code in `rb_big_fdiv_double` rounds it to a double (`dx`) before dividing by the fixnum denominator of 10^12, resulting in `65803600.51312783`, instead of the correctly rounded value, `65803600.513127826`. The `isinf(dx)` test does not cover this case. Moreover, not all fixnums (in 64-bit systems) can be represented exactly as doubles. -- https://bugs.ruby-lang.org/