[squeak-dev] Re: [Vm-dev] [commit][3152] Make sure to compile the SmallFloat64 primitives.

Eliot Miranda eliot.miranda at gmail.com
Wed Nov 26 22:42:39 UTC 2014

Hi Ben,

On Wed, Nov 26, 2014 at 2:27 PM, Ben Coman <btc at openinworld.com> wrote:

> commits at squeakvm.org wrote:
>>  Revision: 3152
>> Author:   eliot
>> Date:     2014-11-26 11:57:25 -0800 (Wed, 26 Nov 2014)
>> Log Message:
>> -----------
>> Make sure to compile the SmallFloat64 primitives.
>>         boxedFloat comment: 'My instances hold 64-bit Floats in heap
>> objects.  This is the only representation on 32-bit systems.  But on 64-bit
>> systems SmallFloat64 holds a subset of the full 64-bit double-precision
>> range in immediate objects.'
>>                 stamp: 'eem 11/25/2014 7:54'.
>>         smallFloat comment: 'My instances represent 64-bit Floats whose
>> exponent fits in 8 bits as immediate objects.  This representation is only
>> available on 64-bit systems, not 32-bit systems.'
> So are SmallFloats converted to BoxedFloats on the fly when an image is
> moved from a 64-bit host to a 32-bit host ?

No; there is no automatic conversion between 32-bit and 64-bit images.
 64-bit Spur images will only be  runnable on 64-bit machines.  There are
scripts that convert 32-bit non-Spur images to 32-bit Spur images and from
32-bit Spur images to 64-bit Spur images, and it would be easy to add a
script that converted from a 64-bit Spur image to a 32-bit Spur image.  But
none of these conversions will be provided "automatically" (e.g. as a
side-effect of starting up an image), although they may be wrapped up in
tools.  Currently the conversion time from 32-bit non-Spur to 32-bit Spur
on a fast laptop is 5 minutes, and IIRC conversion from 32-bit Spur to
64-bit Spur takes a couple of minutes.  So I don't think one will ever want
this to happen automatically.

Further, I hope and expect that we're moving to/have already moved to a
construction-oriented image build process where one will take a
pre-prepared base image of the appropriate pointer width and run scripts to
load packages into them.  So I expect the main use of the Spur 32-bit to
64-bit bootstrap is in preparing base release images.

btw, Does that comment need updating... didn't you go with SmallDouble,
> BoxedDouble?

No.  Bert suggested (IIRC) ImmediateFloat64 and BoxedFloat64 and I went
with SmallFloat64 and BoxedFloat64 for two reasons.  SmallFloat64 because I
like the symmetry with SmallInteger, and because this name scheme
gracefully admits SmallFloat32, BoxedFloat32 and BoxedFloat80 if ever there
was the energy to add them.
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