Bug #8894


Fixnum#quo returns wrong result when given a float

Added by marcandre (Marc-Andre Lafortune) almost 9 years ago. Updated about 5 years ago.

Target version:
ruby -v:


Fixnum#quo is buggy.

2.quo(2.0) # => Rational(2, 2)

  1. Should return a float, not a rational
  2. Moreover, that rational is invalid as it is not reduced.

Noticed by David MacMahon [ruby-core:57121]

Related issues 1 (0 open1 closed)

Related to Ruby master - Bug #5515: Integer#quo(aFloat) の結果が Rational になるClosedmrkn (Kenta Murata)10/30/2011Actions

Updated by marcandre (Marc-Andre Lafortune) almost 9 years ago

Issue is actually with Rational#/ that apparently makes a special case of float values that are "multiples" of the denominator, so that:

Rational(6) / 2.0 # => Rational(6, 2)

Putting aside the bug that the Rational returned is not reduced, I feel it is the wrong to return a Rational for many reasons.

  1. A float is imprecise; other than very special cases one should not obtain exact values whenever one is involved in the calculation.
  2. Inconsistent with Rational(5) / BigDecimal(2) that returns (correctly) a BigDecimal)
  3. Inconsistent with Rational(6) / 1.5, that returns which won't return 4 nor Rational(4)

Is there any reason we should keep that special case?

diff --git a/rational.c b/rational.c
index 652f5ac..f8284d9 100644
--- a/rational.c
+++ b/rational.c
@@ -959,9 +959,6 @@ nurat_div(VALUE self, VALUE other)

        if (isnan(x)) return DBL2NUM(NAN);
        if (isinf(x)) return INT2FIX(0);
  •       if (x != 0.0 && modf(x, &den) == 0.0) {
  •           return rb_rational_raw2(dat->num, f_mul(rb_dbl2big(den), dat->de
  •       }
      return rb_funcall(f_to_f(self), '/', 1, other);

Updated by samu0101 (tatsuro yasukawa) about 5 years ago

  • ruby -v changed from p195 to 2.2

This problem seems to be solved already since I tried this by ruby 2.2 and didn't have any problem.
So we can close this issue.

▼ Result by ruby 2.2

2.quo(2.0) # => 1.0

Rational(6) / 2.0  # => 3.0
Actions #3

Updated by sorah (Sorah Fukumori) about 5 years ago

  • Backport deleted (1.9.3: UNKNOWN, 2.0.0: UNKNOWN)
  • Status changed from Open to Feedback
Actions #4

Updated by marcandre (Marc-Andre Lafortune) about 5 years ago

  • Status changed from Feedback to Closed

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