Part of the advantage of the structs Per is talking about is this: Structs may
be passed as arguments and used as locals elementwise, with no allocation on
the stack. Think of it as guaranteed escape analysis, or guaranteed unboxing.
-- John
On May 28, 2010, at 3:24 AM, Kresten Krab Thorup wrote:
>
>
> On May 27, 1:17 am, Per Bothner <p...@bothner.com> wrote:
>> This is another example of where structs would be helpful. That would
>> allow:
>>
>> struct Integer {
>> int ivalue;
>> int[] iwords;
>>
>> }
> ....
>>
>> Kawa basically does this using a regular class gnu.math.Integer,
>> and "small" Integers pre-allocated. That is one reason Kawa's
>> arbitrary-precision handling is (mostly) noticeably faster than BigInteger.
>> (Some of that could be achieved by further tweaking BigInteger.)
>
> 1: I'm intrigued. How much does this give you?
>
> I can see that you avoid a virtual call for all math operators where
> you can determine the integer-ness of operands; so it does not have to
> choose between SmallInt and BigInt objects. But it comes at the
> overhead of an extra word per integer.
>
> Integer arithmetic (most notably X+1, X-1, and X==<constant>) used in
> loops is currently a noticeable performance issue in Erjang (when
> comparing to the normal erlang implementation using tags). In many
> such cases, I could avoid a virtual call and that does sound
> appealing.
>
> 2: What is the motivation in Kawa to make your own bignum
> implementation. Why not just have
>
> class KawaInteger {
> int ival;
> BigInteger bval;
>
> ...
> }
>
> i.e., fall back on the standard bignum implementation?
>
>
> Kresten
>
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