migrate an old (somewhat useful) basicblock size vector

[nirizr]

I old incarnations of rematch, we've used a feature extractor that proved to be occasionally useful.

The feature extractor was, put simply, a histogram of basic-block sizes.

This could easily be augmented by adding other types of information into the vector, but was useful enough on it's own so seems like a good start.

Additional data piece: External cross-references (cross-references to objects outside the function, usually other functions through calls or global data access).

Tasks:

• Add Vector class
• Add distance matcher (based on HistMatch or brand new one)
• Include external cross references.
• Include types of cross-references in a different vector portion.

A simple example:

  vector = np.zeros((4096,))
  size = 0
  for item_ea in FuncItems(ea):
    if InternalXrefsToItem(item_ea):
      vector[size] += 1
      size = ItemSize(item_ea)
    if InternalXrefsFromItem(item_ea):
      vector[size] += 1
      size = 0
    else:
      size += ItemSize(item_ea)

  if np.sum(vector) > 8:
    return vector
  else:
    return None