PrecisionCascade connections to compression functions

[genevb]

Missing: array of compression levels (contents for cxlevels vector)
Not sure I have everything else correct in TBasket, but it does compile for me.
Makes PR #12 obsolete.

[pcanal]

It comes from the configArray and to extract the information (should probably be done within R__zip....)

if (configArray && configArray->IsPrecisionCascade()) { // just in case something is wrong
    // oups I have not uploaded the implementation yet :(
}

[genevb]

OK....I'll await your implementation and then I'll write the relevant code in RZip.cxx.

[pcanal]

See https://github.com/pcanal/root/pull/13/files#r900478838

[pcanal]

Suggested change

	auto content = reinterpret_cast<ROOT::Internal::PrecisionCascadeConfigArrayContent*>(fConfigArray);
	assert(content->SizeOf() == configsize);
	Int_t *cxlevels = content->GetLevels(); // This an array of size `content->fLen`

[pcanal]

The compression levels are the user provided levels, so they still need offset by 61.

[pcanal]

#include "PrecisionCascadeConfigArrayContent.h" is needed.

[pcanal]

Suggested change

	precisionCascades[i] += nouts[i]; // increment each element by its corresponding nout.
	precisionCascades[i] += nouts[i + 1]; // increment each element by its corresponding nout.

[genevb]

I don't understand the suggestion to look at the nouts value from one ahead. The first thing I do with precisionCascades is push_back the primary buffer, so both it and nouts have the primary buffer first and there should be no offset between them.

[pcanal]

yes, I forgot that early push, so you are right.

[genevb]

These two files are still to be written?
#include "PrecisionCascadeCompressionConfig.h" (from Compression.cxx)
#include "PrecisionCascadeConfigArrayContent.h" (from RZip.cxx)

[pcanal]

I had forgotten to push the file and had misnamed it .... sorry :(

[genevb]

Looks like compilation is happy now on my end, except that it warns that configsize is unused, though it is actually used inside the assert in RZip.cxx. What else is needed before I begin testing? I'll have to figure out how to use the configuration for PrecisionCascade, but presumably I can try the old applyBlast.C macro modified to use a a PrecisionCascade.

[pcanal]

Since it compiles, I will rebase and merge.

[pcanal]

The usage is "simple":

PrecisionCascadeCompressionConfig config( RCompressionSetting::EAlgorithm::kBLAST, { 51, 61 }, true /* want to keep the residual / all the precision);
mybranch->SetCompressionSettings(config);

[pcanal]

@genevb I force pushed to your branch, you probably will have an easier time starting from a new branch for further development.