Float#% bug in cornercases
On my platform, current behavior is:
4.0 % Float::INFINITY # => NaN
4.0.send :%, Float::INFINITY # => 4.0
-0.0 % 42 # => 0.0
-0.0.send(:%, 42) # => -0.0
On some platforms, these might return NaN and 0.0 in all cases.
My proposed behavior is to return 4.0 and -0.0 on all cases and on all platforms.
I'm tempted to assume it is clear that this is bug and that my proposed behavior is the right solution, but let me use my guidelines:
Proposed behavior passes my "strict superiority test" as it is clearly more consistent:
- consistent for different calling methods
- consistent accross platforms
- consistent with 4 % Float::INFINITY
- consistent with the IEEE definition of fmod (see http://pubs.opengroup.org/onlinepubs/007904975/functions/fmod.html )
It is also more intuitive and useful, since:
any_small_number % any_big_number == any_small_number
Current behavior passes the "clear defect test" as it is platform dependent (when it can reasonable be platfom independent). I'll add to the list of "clear defect" criteria the fact that calling an operator directly doesn't yield the same result as using
The proposed solution fails my "straightforward" test as the proposed behavior contradicts part of the documentation which states "x.modulo(y) means x-y*(x/y).floor".
Any objection for me to commit this?
Updated by marcandre (Marc-Andre Lafortune) almost 9 years ago
Additional problem case:
4.2 % 0 # => ZeroDivisionError
4.2 % 0.0 # => NaN
4.2.send :%, 0.0 # => ZeroDivisionError
Because returning NaN is not a useful result and to be consistent with BigDecimal, all three will raise a ZeroDivisionError unless someone has arguments to the contrary.
Yui NARUSE wrote:
About the implementation, flodivmod() should be public but internal API and declare prototype in internal.h,
and use it from insns.def.
Ok, thanks, I will do that.
Updated by naruse (Yui NARUSE) almost 9 years ago
- Status changed from Open to Closed
- % Done changed from 0 to 100
This issue was solved with changeset r35176.
Marc-Andre, thank you for reporting this issue.
Your contribution to Ruby is greatly appreciated.
May Ruby be with you.
merge revision(s) 35013:
* numeric.c: fix flodivmod for cornercases [Bug #6044] add ruby_float_mod * insns.def (opt_mod): use ruby_float_mod * internal.h: declare ruby_float_mod * test/ruby/test_float.rb: tests for above * test/ruby/envutil.rb: create helper assert_is_minus_zero