[Vm-dev] [Fwd: Re: [Pharo-dev] Float hierarchy for 64-bit Spur]

Ben Coman btc at openInWorld.com
Fri Nov 21 04:42:54 UTC 2014

Eliot Miranda wrote:
> On Thu, Nov 20, 2014 at 7:00 PM, Ben Coman <btc at openinworld.com 
> <mailto:btc at openinworld.com>> wrote:
>     Eliot Miranda wrote:
>         Hi All,
>             64-bit Spur can usefully provide an immediate float, a
>         61-bit subset of the ieee double precision float. 
>     I wonder if class SmallDouble would be more intention revealing?
>     In practice 61 bits will be "more than enough"(tm) for anyone. But I
>     can envisage in a business environment environment software needing
>     to comply with (sometimes irrelevant) feature checklists, with one
>     of those likely being full 64 bit compliant IEEE Doubles.  Can we
>     have such a class, to which 61 bit floats are auto-promoted as required?
> Just as SmallInteger is seamless with the large integers, so SmallFloat 
> is seamless with boxed Float.  The SmallFloat representation is used 
> where ever possible, since it is faster both to decode (no memory fetch) 
> and to encode (no allocation).  But operations overflow into the boxed 
> representation if outside the SmallFloat range.

(btw, rather than SmallFloat and BoxedFloat, I think SmallFloat and 
LargeFloat would align better with the Integer hierarchy.)

So I understand that immediate types will overflow to boxes types :)

To try to be more clear, integers don't have a well defined size/format. 
  It varies with architecture word size.  So SmallInteger and 
LargeInteger are reasonable descriptions.  But floats have a well 
defined format defined by IEEE. Since you are pivoting around the IEEE 
Double format (you define it as "61-bit subset of the ieee double 
precision float"), rather than generic SmallFloat and LargeFloat, use 
SmallDouble and LargeDouble. (anyway, maybe I'm off track. Its not a big 

>     My first few pages of search results lead to a few references in
>     conversation, but nothing that described what a boxed float is. Can
>     someone explain?
> Boxed datatypes are those where the data is held in a structure (e.g. an 
> object) and accessed throguh a pointer.  So most Smalltalk objects are 
> "boxed", for example, large integers, points, etc.  But some datatypes 
> (immediate SmallIntegers, and in Spur, the Characters, and in languages 
> like C, all basic numeric types) are represented as pure values.


cheers -ben

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