[ruby-core:57127] [ruby-trunk - Bug #8894] Fixnum#quo returns wrong result when given a float

Issue #8894 has been updated by marcandre (Marc-Andre Lafortune).


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);
     }

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Bug #8894: Fixnum#quo returns wrong result when given a float
https://bugs.ruby-lang.org/issues/8894#change-41733

Author: marcandre (Marc-Andre Lafortune)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 
ruby -v: p195
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


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]


-- 
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