private void updateSelectionToViewportTop() {
		
		Pair filePos = model.getFilePositionForRow(getViewportPositionAsRow());
		if (filePos == null) {
			return;
		}
		
		long filePosForTopRow = filePos.getStart();
		model.selectedByteStart = filePosForTopRow;
		table.restoreSelection();
	}
Sets the first row in the viewport to be the start of the current selection range.  The 
end of the selection range remains untouched.
Ghidra/Framework/Project/src/main/java/ghidra/framework/main/logviewer/ui/ViewportUtility.java