[Vm-dev] Spur Object 64 bit format

Igor Stasenko siguctua at gmail.com
Tue Nov 12 11:37:26 UTC 2013

And let me remind you what i proposed back then:

About immediates zoo.

Keep in mind, that the more immediates we have, the more complex
tends to be.

I would just keep 2 data types:
 - integers
 - floats

and third, special 'arbitrary' immediate , which seen by VM as a 60-bit
The interpretation of this value depends on lookup in range-table,
where developer specifying the correspondence between the value
interval and class:
[min .. max] -> class

intervals, of course, cannot overlap.
Determining a class of such immediate might be slower - O(log2(n)) at
best (where n is size of range table), but from other side,
how many different kinds of immediates you can fit into 60-bit value?
Right, it is 2^60. Much more than proposed 8 isn't? :)

And this extra cost can be mitigated completely by inline cache.
- in case of regular reference, you must fetch the object's class and
then compare it with one, stored in cache.
- in case of immediate reference, you compare immediate value with min
and max stored in cache fields.
And if value is in range, you got a cache hit, and free to proceed.
So, its just 1 extra comparison comparing to 'classic' inline cache.

And, after thinking how inline cache is organized, now you can scratch
the first my paragraph related to  immediates!
We really don't need to discriminate between small integers/floats/rest!!
They could also be nothing more than just one of a range(s) defined in
our zoo of 'special' immediates!

So, at the end we will have just two kinds of references:
 - zero bit == 0 -- an object pointer
 - zero bit == 1 -- an immediate


We can have real zoo of immediates, and simple implementation to support
And not saying that range-table is provided by language-side, so we're
free to rearrange them at any moment.

And of course, it doesn't means that VM could not reserve some of the
ranges for own 'contracted'
immediates, like Characters, and even class reference for example.
Think about it :)

On 12 November 2013 11:56, Henrik Johansen <henrik.s.johansen at veloxit.no>wrote:

> On 12 Nov 2013, at 11:55 , Henrik Johansen <henrik.s.johansen at veloxit.no>
> wrote:
> nterest ~= time and: [skills]
> OT: I swear, missing parenthesis will be the death of me!

Best regards,
Igor Stasenko.
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