Loop to swap data around in Data Processor?

[clemarescx]

Hello,
thanks a lot for ImHex! Not sure if I'm having skill issues with the Data Processor - I'm new to node-based scripting - or if it's possible at all, but here goes:

I need to preprocess binary data as follow:

1. read data in 10 bytes chunks
2. reverse those 10 bytes
3. swap bytes 2 by 2

Example:

// 10-byte rows
00 01 02 03 04 05 06 07 08 09
0A 0B 0C 0D 0E 0F 10 11 12 13

should become

08 09 06 07 04 05 02 03 00 01
12 13 10 11 0E 0F 0C 0D 0A 0B

The equivalent in a pseudo C# code would be:

byte[] data = someData;
const int rowLength = 10;
int rowsCount = data.Length / rowLength; // assume that the length is always evenly dividable by 10
for(int i = 0; i < rowsCount; i++)
{
    int offset = i * rowLength;
    byte[] row = data.Slice(offset, length: rowLength); // first row would be [ 01 02 03 04 ... ]
    row.Reverse();  // first row would now be [09 08 07 06 ...]
    for(int j = 0; j < row.Length; j += 2)
    {
        // swap bytes 2 by 2
        (row[j+1], row[j]) = (row[j], row[j+1]);
    }
    // first row would now be done: [08 09 06 07...]
    data.Write(offset, row, count: rowLength);
}

I see that there are node functions that I could use like Slice and Reverse, but I don't know how to look back to read from the Read buffer or a data buffer in chunks with an incremented offset... Or how to loop at all in general.
Any help would be appreciated.

[isti115]

I am trying to do something similar to this, and I see that a Loop node has been added since then by @WerWolv, but cannot figure out how to use it in any meaningful way. 🤔

[Lil-Nugs]

The code for the loop node just seems to output whatever is inputted every iteration?

Or if you have start == end, it'll just output the initial value? What's the point of this node?

ImHex/plugins/builtin/source/content/data_processor_nodes/control_nodes.cpp

Lines 123 to 139 in 58228e0

	void process() override {
	if (!m_started) {
	m_started = true;
	auto start = this->getIntegerOnInput(0);
	auto end = this->getIntegerOnInput(1);
	m_value = this->getIntegerOnInput(2);
	for (auto value = start; value < end; value += 1) {
	this->resetProcessedInputs();
	m_value = this->getIntegerOnInput(3);
	}
	m_started = false;
	}
	this->setIntegerOnOutput(4, m_value);
	}