bah excuse the grammar...
I constantly invert now vs know and where vs were, I wish your brain is
equipped with auto-correction.

Le dim. 3 mai 2020 à 17:20, Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com> a écrit :

>
>
> 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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