Hi Ben,

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

commits@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.

best,

Eliot