[webkit-dev] BigInt implementation

[Filip Pizlo]

Seems like V8’s is an ok place to start. Maybe all you’d have to do is remove the accurate GC artifacts (Handle and such). 

-Filip

> On Oct 19, 2017, at 2:31 AM, Daniel Ehrenberg <littledan at igalia.com> wrote:
> 
> On 2017-10-19 03:18, Filip Pizlo wrote:
>>> On Oct 18, 2017, at 5:50 PM, Caio Lima <ticaiolima at gmail.com> wrote:
>>> 
>>> Hi WebKittens.
>>> 
>>> I’m planning to start implement JS BigInt proposal on JSC, however I
>>> would like to sync with you the way you are planning to implement such
>>> feature.
>>> 
>>> Right now, I’m thinking in implement BigInt operations into C++
>>> (possibly on WTF?) and make the JSBigInt use this implementation.
>> 
>> We need something GC-optimized from the start since that will
>> determine a lot of the details. So, I don’t think that a WTF
>> implementation is appropriate. It should be a JSCell from day one.
>> 
>>> As I
>>> have checked with some other implementors, some of them are going to
>>> use libgmp (SpiderMonkey case), but I don’t think its license (GPLv2)
>>> aligns with WebKit’s license and I heard that V8 is implementing their
>>> BigInt lib as well. By now, I’m thinking in implement a proof of
>>> concept and then, optimize the BigInt lib part. So, what I would like
>>> to collect from you is: Is there any problem start work on that
>>> feature?
>> 
>> We should do a GC-optimized bigint. If there was a great library that
>> had the right license, we could port it to allocate using our GC. I
>> don’t have a strong view on whether we should write our own from
>> scratch or use somebody else’s as a starting point (so long as the
>> license is ok).
> 
> I'm not sure if there is such a great library. The other programming
> languages I've seen BigInt implementations in were either based on
> external libraries and didn't have GC integration, or were based on
> writing their own BigInt library or forking it from another programming
> language. I'm not aware of an existing BigInt library which permits GC
> integration.
> 
> If GC optimization weren't needed,then libtommath [1] could be a good
> choice. However, this does not store BigInts in a single contiguous
> memory region, but rather has a header and discontiguous payload. I
> believe Jordi Montes (cc'd) is working on a library based on libtommath
> which would work more like this, but I'm not sure how far along it is,
> or how well it would integrate into JSC GC.
> 
> If you want to follow the tradition of forking another library, one
> option would be to start with V8's. It's relatively new and not quite
> finished, but the nice thing is that it implements the same operations
> that will be needed in JSC. [2]
> 
> [1] http://www.libtom.net/LibTomMath/
> [2] https://github.com/v8/v8/blob/master/src/objects/bigint.cc
>> 
>> I don’t have any objection to you working on this.
>> 
>> -Filip
>> 
>>> 
>>> It is one of the proposals that I’ve made to my Coding Experience at
>>> Igalia, so I will also have the support of developers from there,
>>> since they are implementing it on SpiderMonkey and the spec champion
>>> is also in the team.
>>> 
>>> Regards,
>>> Caio.
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>