Issue #22246 has been updated by rgburger (Robert Burger). This might fix it: ``` double rb_big_fdiv_double(VALUE x, VALUE y) { if (FIXNUM_P(y)) { return big_fdiv_int(x, rb_int2big(FIX2LONG(y))); } else if (RB_BIGNUM_TYPE_P(y)) { return big_fdiv_int(x, y); } else if (RB_FLOAT_TYPE_P(y)) { double dy = RFLOAT_VALUE(y); if (isnan(dy)) return dy; return big_fdiv_float(x, y); } else { return NUM2DBL(rb_num_coerce_bin(x, y, idFdiv)); } } ``` ---------------------------------------- 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-118688 * 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/