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| author | Andrew Lamoureux <andrew@vector35.com> | 2019-03-19 17:32:44 -0400 |
|---|---|---|
| committer | Rusty Wagner <rusty@vector35.com> | 2019-03-20 13:00:17 -0400 |
| commit | 24ead55316ac8497df5842caf4e1d51f2b799787 (patch) | |
| tree | 3dfdfae8a076445c9d24bf6d1b40e57f36ebf94a /python/examples/kaitai/vlq_base128_be.py | |
| parent | 411acbaa4a1d217e731d3df0b189445117be3b26 (diff) | |
kaitai: adjustments and rearrangements for python2/3 compat
Diffstat (limited to 'python/examples/kaitai/vlq_base128_be.py')
| -rw-r--r-- | python/examples/kaitai/vlq_base128_be.py | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/python/examples/kaitai/vlq_base128_be.py b/python/examples/kaitai/vlq_base128_be.py new file mode 100644 index 00000000..69dce835 --- /dev/null +++ b/python/examples/kaitai/vlq_base128_be.py @@ -0,0 +1,102 @@ +# This is a generated file! Please edit source .ksy file and use kaitai-struct-compiler to rebuild + +from pkg_resources import parse_version +from .kaitaistruct import __version__ as ks_version, KaitaiStruct, KaitaiStream, BytesIO +import collections + + +if parse_version(ks_version) < parse_version('0.7'): + raise Exception("Incompatible Kaitai Struct Python API: 0.7 or later is required, but you have %s" % (ks_version)) + +class VlqBase128Be(KaitaiStruct): + """A variable-length unsigned integer using base128 encoding. 1-byte groups + consist of 1-bit flag of continuation and 7-bit value chunk, and are ordered + "most significant group first", i.e. in "big-endian" manner. + + This particular encoding is specified and used in: + + * Standard MIDI file format + * ASN.1 BER encoding + + More information on this encoding is available at + https://en.wikipedia.org/wiki/Variable-length_quantity + + This particular implementation supports serialized values to up 8 bytes long. + """ + SEQ_FIELDS = ["groups"] + def __init__(self, _io, _parent=None, _root=None): + self._io = _io + self._parent = _parent + self._root = _root if _root else self + self._debug = collections.defaultdict(dict) + + def _read(self): + self._debug['groups']['start'] = self._io.pos() + self.groups = [] + i = 0 + while True: + if not 'arr' in self._debug['groups']: + self._debug['groups']['arr'] = [] + self._debug['groups']['arr'].append({'start': self._io.pos()}) + _t_groups = self._root.Group(self._io, self, self._root) + _t_groups._read() + _ = _t_groups + self.groups.append(_) + self._debug['groups']['arr'][len(self.groups) - 1]['end'] = self._io.pos() + if not (_.has_next): + break + i += 1 + self._debug['groups']['end'] = self._io.pos() + + class Group(KaitaiStruct): + """One byte group, clearly divided into 7-bit "value" chunk and 1-bit "continuation" flag. + """ + SEQ_FIELDS = ["b"] + def __init__(self, _io, _parent=None, _root=None): + self._io = _io + self._parent = _parent + self._root = _root if _root else self + self._debug = collections.defaultdict(dict) + + def _read(self): + self._debug['b']['start'] = self._io.pos() + self.b = self._io.read_u1() + self._debug['b']['end'] = self._io.pos() + + @property + def has_next(self): + """If true, then we have more bytes to read.""" + if hasattr(self, '_m_has_next'): + return self._m_has_next if hasattr(self, '_m_has_next') else None + + self._m_has_next = (self.b & 128) != 0 + return self._m_has_next if hasattr(self, '_m_has_next') else None + + @property + def value(self): + """The 7-bit (base128) numeric value chunk of this group.""" + if hasattr(self, '_m_value'): + return self._m_value if hasattr(self, '_m_value') else None + + self._m_value = (self.b & 127) + return self._m_value if hasattr(self, '_m_value') else None + + + @property + def last(self): + if hasattr(self, '_m_last'): + return self._m_last if hasattr(self, '_m_last') else None + + self._m_last = (len(self.groups) - 1) + return self._m_last if hasattr(self, '_m_last') else None + + @property + def value(self): + """Resulting value as normal integer.""" + if hasattr(self, '_m_value'): + return self._m_value if hasattr(self, '_m_value') else None + + self._m_value = (((((((self.groups[self.last].value + ((self.groups[(self.last - 1)].value << 7) if self.last >= 1 else 0)) + ((self.groups[(self.last - 2)].value << 14) if self.last >= 2 else 0)) + ((self.groups[(self.last - 3)].value << 21) if self.last >= 3 else 0)) + ((self.groups[(self.last - 4)].value << 28) if self.last >= 4 else 0)) + ((self.groups[(self.last - 5)].value << 35) if self.last >= 5 else 0)) + ((self.groups[(self.last - 6)].value << 42) if self.last >= 6 else 0)) + ((self.groups[(self.last - 7)].value << 49) if self.last >= 7 else 0)) + return self._m_value if hasattr(self, '_m_value') else None + + |
