WordX/IntX wrap Word#/Int#?

Ben Gamari ben at smart-cactus.org
Mon Jun 12 01:43:16 UTC 2017

Joachim Breitner <mail at joachim-breitner.de> writes:

> Hi,
> Am Sonntag, den 11.06.2017, 10:44 -0400 schrieb Ben Gamari:
>> This is certainly one consideration. Another is that you would also
>> need to teach the garbage collector to understand closures with sub-
>> word-size fields. Currently we can encode whether each field of a
>> closure is a pointer or not with a simple bitmap. If we naively
>> allowed smaller fields we would need to increase the granularity of
>> this representation to encode bytes.
>> Of course, one way to work around this would be to impose an
>> invariant that guarantees that pointers are always word-aligned. Then
>> we would probably want to shuffle sub-word sized fields, allowing two
>> Word16s to inhabit a single word.
> that is not an issue; we already sort field into pointers first, and
> non-pointers later. So all pointers are at the beginning and nicely
> aligned, and all the non-pointer data can follow in whatever weird
> format. The GC only needs to know how many words in total are used by
> the non-pointer data.
Ahh, great point. I stand corrected.


- Ben

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