[gambit-list] Tweak possible to "emulate" 64bit features on a 32bit architecture?

Marc Feeley feeley at iro.umontreal.ca
Sun Aug 7 08:34:43 EDT 2016


Forcing 64 bit “words” on a 32 bit machine should be relatively straightforward to implement, but I question the utility of this (factor of 2 space usage).  Better would be to change the object representation so that the header of objects would be always 64 bits (or better, split into a 32 bit length and 32 bit type and GC flags).  The implementation complexity of both is about the same (roughly 2 days of work).  However, too much work for me right now given the low need for this feature.

Aren’t 32 bit architectures pretty much a thing of the past?  These days, even embedded systems are 64 bit architectures.

Marc


> On Aug 3, 2016, at 3:49 AM, Adam <adam.mlmb at gmail.com> wrote:
> 
> Dear Marc,
> 
> Gambit on 32bit architectures suffer badly of the limitations on maximum string, vector and also fixnum sizes.
> 
> For some uses, this is more than enough as reason to disqualify 32bit architecture use altogether.
> 
> 
> A thought struck me the other day - the reason for those low limits on 32bit architectures, is that Gambit delivers the native integer/pointer size of the underlying architecture, and that leads to those limitations because of how Gambit's type system is built. You could say that the overarching reason is speed.
> 
> My thought is, if a given user would like to take the speed argument out of the equation,
> 
> Would it be possible for you to easily provide a "forced 64bit word" compilation mode for Gambit, hence lifting the string, vector and fixnum size limits far beyond their current ones of 4M-chars, 16MB u8vector, and is it 2^29 as max fixnum value.
> 
> (The string and u8vector limits are the central concerns really.
> 
> The effect on fixnum would be higher speed of computation in the 2^29..2^61 interval at the cost of slightly lower speed in the 0..2^29 interval.)
> 
> This would only be relevant to run on some fairly standard architecture and platform.
> 
> 
> If the tweak would be possible, would Gambit's total live objects be able to amount to 2GB or 4GB, or how much?
> 
> Thanks!
> 




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