Memcmp is not implemented

[d0c-s4vage]

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Checklist

• I have included the [relevant portions of the] 010 template used that caused the bug
• I have filled out the environment section

Environment

Platform

• Windows
• Mac
• Linux
• Other (please specify)

Python Version

• Python 2.7
• Python 3.4
• Python 3.5
• Python 3.6
• Python 3.7
• Python 3.8
• Other (please specify)

Describe the bug

Memcmp isn't implemented

Stack Trace

Traceback (most recent call last):
  File "/tmp/venv3/bin/pfp", line 8, in <module>
    sys.exit(main())
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/__main__.py", line 55, in main
    keep_successful=args.keep,
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/__init__.py", line 91, in parse
    printf=printf,
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 788, in parse
    res = self._run(keep_successful)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 992, in _run
    traceback,
  File "/tmp/venv3/lib/python3.6/site-packages/six.py", line 695, in reraise
    raise value.with_traceback(tb)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 965, in _run
    res = self._handle_node(self._ast, None, None, self._stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1117, in _handle_file_ast
    self._handle_node(child, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 2341, in _handle_while
    self._handle_node(node.stmt, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 2155, in _handle_compound
    self._handle_node(child, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1339, in _handle_decl
    field._pfp__init(stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 126, in _pfp__init
    self._pfp__interp._handle_node(decls, ctxt=self, stream=stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1636, in _handle_struct_decls
    self._handle_node(decl, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 2283, in _handle_if
    cond = self._handle_node(node.cond, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1802, in _handle_binary_op
    left_val = self._handle_node(node.left, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 1074, in _handle_node
    res = self._node_switch[node.__class__](node, scope, ctxt, stream)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/interp.py", line 2122, in _handle_func_call
    return func.call(func_args, ctxt, scope, stream, self, node.coord)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/functions.py", line 79, in call
    res = self.func(args, ctxt, scope, stream, coord)
  File "/tmp/venv3/lib/python3.6/site-packages/pfp/native/compat_string.py", line 140, in Memcmp
    raise NotImplementedError()
pfp.errors.PfpError:
Exception at tests/templates/MP4.bt:53

To Reproduce

Use the MP4.bt template from d0c-s4vage/py010parser#17 (MP4.txt)

Expected Behavior

The MP4 template should be able to be used.

Implementation/Fix Notes/Thoughts

Implement the Memcmp function in native/compat_string.py: https://github.com/d0c-s4vage/pfp/blob/master/pfp/native/compat_string.py#L137