Le dim. 3 mai 2020 à 17:13, Tobias Pape <Das.Linux at gmx.de> a écrit :

>
> > On 03.05.2020, at 15:52, Nicolas Cellier <
> nicolas.cellier.aka.nice at gmail.com> wrote:
> >
> > Hi Subbu,
> > Yes those raw bits are somehow like immediates, but not exactly...
>
> So the name maybe should include "raw"?
> :D
> -t
>

Yes, that was the first name that came in my mind.
>From the abstract superclass POV, those are raw bits.
Only subclass really now how to interpret those bits as value objects.
I don't know why I then changed my mind...
Maybe because RawBits does not convey the meaning of FixedWidth.
Note that the class query is #isBits. So the AbstractBitsArray is somehow
in line with that.

>
> > Immediates are objects having their value encoded into the pointer slot
> (either in 4 or 8 bytes, according to 32bits or 64bits VM word size).
> > Currently, this covers only SmallInteger, Character and SmallFloat on
> 64bits.
> >
> > Here we have values encoded into slots of 1, 2, 4 or 8 bytes, but not
> into an object oriented pointer slot.
> > Technically, #(1 2.0 $3) is an Array of immediates, while ((ColorArray
> with: Color black) first) is not an immediate...
> > So even if it is the same notion of encoded value, it's not an exact
> match...
> >
> > Concerning the use cases, I effectively want to use such bit arrays for
> fast data transfer.
> > For example, it is useful for FFI I use exclusivily this kind of array
> for Smallapack...
> > But also when reading big files in Matlab, National Instrument TDMS or
> HDF5 format.
> > it really helps to have all the possible flavours for common elementary
> types of values.
> > Otherwise, I have to use an intermediate ByteArray, or pointers to
> external heap via FFI (like I did in Smallapack).
> >
> > More than often, the data transfer can handle offset and stride via a
> BitBlt tricks (unless we have an odd layout).
> > This enables extracting a single "column" or bloc of data from a big
> file with a single copy.
> > I may need to extend BitBlt to cope with all the available bit-widths,
> not just 8 (byte) or 32 (word) though.
> >
> > Also, those formats offer packed and contiguous memory layout which is
> an advantage too when dealing with large chunks of data.
> > Especially if we have vectorized primitives operating on the arrays.
> >
> > Also, creating non-immediate objects on the fly thru #at: #at:put: is
> very efficient if VM has generation scavenger because those objects are
> generally short-lived.
> > While retaining all the pointers to a whole collection of non immediate
> objects is putting a lot of pressure on the garbage collector.
> >
> > The advantage somehow diminish with the advent of 64bits VM: most values
> can be immediates, so we have quasi-contiguous data at a few exceptions,
> and not so much GC pressure.
> > But still, the primitives can operate on raw bits, without having to
> handle the immediate tag, nor exceptional (non immediate) values.
> >
> > For the anecdote, in the 90s, I started to experiment some crashes in
> objectworks/visualworks when handling large Arrays of Float.
> > The console would only report: *out of memory*.
> > With increasing processor speed, the memory where exhausted before the
> low space monitoring process had a chance to handle the situation.
> > I then decided to handle all my Arrays of Float (Double) thru some
> UninterpretedBytes and ad-hoc primitives for at: at:put:
> > Since then, I never came back to pointer oriented arrays: if we want
> Smalltalk to scale, we need those basic objects  :)
> >
> >
> > Le dim. 3 mai 2020 à 06:50, K K Subbu <kksubbu.ml at gmail.com> a écrit :
> > On 02/05/20 5:41 pm, commits at source.squeak.org wrote:
> > > Nicolas Cellier uploaded a new version of Collections to project The
> Inbox:
> > > http://source.squeak.org/inbox/Collections-nice.891.mcz
> > >
> > > ==================== Summary ====================
> > >
> > > Name: Collections-nice.891
> > > Author: nice
> > > Time: 2 May 2020, 7:40:45.298967 pm
> > > UUID: 08510be0-8293-6744-959d-c1d41bc13ae1
> > > Ancestors: Collections-nice.890
> > >
> > > Experimental - For discussion
> > >
> > > Group some (most) non-pointers collections under an abstract
> FixedBitWifthArray.
> > > I know, the name is hard to pronounce and thus ugly: it's opened to
> discussion.
> > >
> > > This enables factorization of some methods, for example the trick for
> atAllPut:
> > > Also notice that most methods are shared between FloatArray and
> Float64Array.
> >
> > How about ImmediateWord/ImmediateObject and an ImmediateArray (an array
> > consisting only of Immediate elements)? It would be consistent with
> > isImmediateClass method.
> >
> > An object chunk could be checked at loading time to see if it needs to
> > be converted from immediate to pointers or vice versa. In the typical
> > case, this will be a nop. But if the image is moved to a different host
> > type (say from 64b to 32b or from x86 to ARM), then some immediate
> > numbers may be converted into pointers or vice versa. If this increases
> > loading time for large images, then the image may be saved locally.
> >
> > This is just a strawman. I haven't really thought through all its
> > implications.
> >
> > Regards .. Subbu
> >
> >
>
>
>
>
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