Re: Using Enumerated Types as Array Indexes
On 08/20/2011 01:11 AM, Andreas Leitgeb wrote:
Robert Klemme<shortcutter@googlemail.com> wrote:
On 19.08.2011 22:05, Andreas Leitgeb wrote:
Robert Klemme<shortcutter@googlemail.com> wrote:
All solutions to fix remainder into modulo but keep the wrap around
which have been proposed so far share a common disadvantage: if the
number range is not a multiple of the divisor the value distribution
will not be uniform.
The solution I used to fix this employed a do while loop and
compareAndSet() to reset the value to the beginning of the range (0 in
this case) in a thread safe manner.
There's a much simpler "meta-way" to fix it: just stick to powers of
2 for the array length - then the overflow *does* always happen at a
multiple of the divisor and the value distribution uniform :-)
I reckon you do not mean that suggestion serious. Just in case:
limiting to powers of 2 was not an option here. And if it was, I would
not have used modulo or AtomicInteger's features but just used binary&
to cut off leading bits.
Of course I don't know the wider context, but to me it seemed as if
a power-of-2 sized array would be such a natural choice, that you'd
That never occurred to me. Limiting to powers of 2 does have some
advantages in some situation but it's certainly nothing I would consider
"natural" generally.
surely use one, anyway, already. Under these circumstances, (n % N)
would have seemed to be the same as (n& (N-1)), yet shorter and
clearer - except, as then learned, for negative n ...
May I ask, what other entity imposes the array length on you, and why
choosing the next larger power of 2 will not do?
The value is user configurable and limiting to powers of 2 as valid
values would reduce the range of possible values unnecessarily
especially since the value is resource intensive - so the difference
between 6 and 8 could be significant. That's also why silently
adjusting was not an option.
Kind regards
robert
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