Bug #3609
closedFloat Infinity comparisons in 1.9
Description
=begin
The way <=> works on pretty much everything in Ruby
is that if a <=> b return 0, 1, or 1, it completely
determines the entire set of comparisons
a==b, a>=b, a>b, a<=b, a<b,
b<=>a, b==a, b>=a, b>a, b<=a, b<a.
(and if it doesn't, a==b/b==a will be both true or both false,
everything else will raise exception or return false/nil)
Float Infinity in 1.9 but not 1.8 seems to violate that.
Comparing it with strange things returns 1 if it's on the left,
but raises exception in every other way.
inf = 1.0/0.0
inf <=> "foo" # => 1
"foo" <=> inf # ArgumentError: comparison of String with Float failed
This interacts even more strangely with very large bignums and the
"if bignum converts to float, it equals that float" thing Ruby currently does
[rubycore:31376].
inf=1.0/0.0
huge=10**500
Consistent either way:
inf >= huge # => true
huge <= inf # => true
inf < huge # => false
huge > inf # => false
Consistent only with mathematical interpretation
(or with "equal if converts, except for special cases
for infinities"):
inf <=> huge # => 1
huge<=> inf # => 1
huge < inf # => true
huge >= inf # => false
Consistent only with "equal if converts":
inf == huge # => true
huge == inf # => true
inf > huge # => false
inf <= huge # => true
Now I'd definitely prefer mathematical interpretation of floats,
to "equal if converts", but this just doesn't make any sense
no matter which way I look at it.
=end
Updated by marcandre (MarcAndre Lafortune) almost 12 years ago
 Category set to core
=begin
I completely agree that Math::Float <=> "foo" should return nil.
The current behavior is due to r23742 which wanted to address the fact that Float::Infinity <=> BigDecimal("1.0E500") was returning 0 (I think, see rubydev:38681)
To fix Float::Infinity <=> "foo", the minimum that must be done is:
diff git a/numeric.c b/numeric.c
index eb3d4be..daa5d6d 100644
 a/numeric.c
+++ b/numeric.c
@@ 1038,7 +1038,7 @@ flo_cmp(VALUE x, VALUE y)
break;
default:

if (isinf(a) && (!rb_respond_to(y, rb_intern("infinite?")) 

if (isinf(a) && (rb_respond_to(y, rb_intern("infinite?")) && !RTEST(rb_funcall(y, rb_intern("infinite?"), 0, 0)))) { if (a > 0.0) return INT2FIX(1); return INT2FIX(1);
The fact that <=> is not consistent with <, etc, is also a problem that need to be fixed. Either the special treatment should be extended to the other comparison operators, or the special treatment for infinity should be removed from <=>
I believe the special treatment should be removed altogether:
diff git a/numeric.c b/numeric.c
index eb3d4be..a6c5360 100644
 a/numeric.c
+++ b/numeric.c
@@ 1038,11 +1038,6 @@ flo_cmp(VALUE x, VALUE y)
break;
default:

if (isinf(a) && (!rb_respond_to(y, rb_intern("infinite?")) 

!RTEST(rb_funcall(y, rb_intern("infinite?"), 0, 0)))) {

if (a > 0.0) return INT2FIX(1);

return INT2FIX(1);

}} return rb_num_coerce_cmp(x, y, rb_intern("<=>"));
return rb_dbl_cmp(a, b);
I understand the intent, but the fact is that Float::INFINITY is a very big value, but since it is the float representation of a lot of big real numbers, like 10400, 1040000 or even Infinity itself, I feel that r23742 introduces many inconsistencies. For example, currently:
1.0e200 ** 2 <=> BigDecimal("1.0e99999") # => 1
=end
Updated by nobu (Nobuyoshi Nakada) almost 12 years ago
 Status changed from Open to Closed
 % Done changed from 0 to 100
=begin
This issue was solved with changeset r28751.
Tomasz, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
=end
Updated by nobu (Nobuyoshi Nakada) almost 12 years ago
 Status changed from Closed to Assigned
 Assignee set to yugui (Yuki Sonoda)
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=end
Updated by mame (Yusuke Endoh) almost 12 years ago
 Status changed from Assigned to Closed
=begin
Backported at r28788.
=end
Updated by marcandre (MarcAndre Lafortune) almost 12 years ago
 Status changed from Closed to Open
 Assignee deleted (
yugui (Yuki Sonoda))
=begin
The patch fixes comparison with non numerics, but doesn't address the rest of the issues:
 inconsistency with mathematics
 inconsistency with other operators like <, <=, ..
Is there objection to removing the special test for infinity?
diff git a/numeric.c b/numeric.c
index 740ef54..ed159ce 100644
 a/numeric.c
+++ b/numeric.c
@@ 1039,15 +1039,6 @@ flo_cmp(VALUE x, VALUE y)
break;
default:

if (isinf(a) && (i = rb_check_funcall(y, rb_intern("infinite?"), 0, 0)) != Qundef) {

if (RTEST(i)) {

int j = rb_cmpint(i, x, y);

j = (a > 0.0) ? (j > 0 ? 0 : +1) : (j < 0 ? 0 : 1);

return INT2FIX(j);

}

if (a > 0.0) return INT2FIX(1);

return INT2FIX(1);

}} return rb_num_coerce_cmp(x, y, rb_intern("<=>"));
return rb_dbl_cmp(a, b);
=end
Updated by mame (Yusuke Endoh) almost 12 years ago
 Target version set to 2.0.0
=begin
Hi,
The patch fixes comparison with non numerics, but doesn't address the rest of the issues:
Indeed. I thought nobu aimed to fix only the obvious wrong condition.
Is there objection to removing the special test for infinity?
It looks like a design issue rather then code bug. So I change this
to 1.9.x.
I have no objection against removal of the code in trunk. Though,
I like rather extend the special test to other operators than remove.

Yusuke Endoh mame@tsg.ne.jp
=end
Updated by shyouhei (Shyouhei Urabe) over 11 years ago
 Status changed from Open to Closed
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