Thanks for looking into that Vincent.
My 2 cents, for what it is worth:
- NEVER use floating point for equality checks. Ever.
Not only is the precision misleading (Radix 2 - isms/ etc.), but 32 vs. 64
... etc. get in the way, quite often, in fact
- If NSDate in particular, "always use NSDate methods of time calculations
whenever possible"
else
- to_i (as Vincent lists)
On Wed, 2 Feb 2011 08:20:40 +0900
Vincent Isambart <vincent.isamb...@gmail.com> wrote:
My conclusions,
- 0.7 and 0.9 fix return the correct time now, 0.9 fix can't do necessary
time arithmetic
- Ruby Time.to_f is broken in all 3 versions
- Bignum.to_f is broken in all 3 versions
- I believe the to_f method is behind all of these problems but i haven't
had time to find the problem nor
a solution.
Your problems with #to_f are due to the fact that 32-bit MacRuby stores
floats in 30 bits (MRI stores them in objects in 64 bits, 64-bit MacRuby
stores them in 62 bits). The reason is mainly speed related (and we also
don't have to garbage-collect them). At some time I think we had 32-bit mode
using objects for storing them like MRI, and 64-bit mode using 62 bits but we
decided to handle them the same way in both modes to have less code to
maintain.
Seeing that very few people using 32-bit (and we will probably stop
"supporting" it after 0.9), you will never get the precision you want from
them. What you can do with MacRuby's current state though:
- if you don't need sub-second precision, use #to_i and do computations in
integers (you can us Time.at to bring them back in Time instances),
- if you really need sub-second prevision, you would have to use BigDecimal.
To convert a Time into BigDecimal: BigDecimal.new("%d.%06d" % [time.tv_sec,
time.tv_usec]). To convert a BigDecimal back to time: Time.at(bd.to_i, (bd *
1000000).to_i % 1000000)
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