Initial commit. Implemented reading of variable size integers, element sizes, and...

diff --git a/.gitignore b/.gitignore
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+++ b/.gitignore
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+*.pyc

diff --git a/ebml/__init__.py b/ebml/__init__.py
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index 0000000..e69de29

diff --git a/ebml/core.py b/ebml/core.py
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+++ b/ebml/core.py
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+import warnings
+from .exceptions import *
+
+
+EBMLMaxSizeLength = 8
+EBMLMaxIDLength = 4
+
+
+def _read_vint_to_bytearray(stream, max_width=EBMLMaxSizeLength):
+       """
+       
+       Reads a vint from stream and returns a bytearray containing all of the bytes without doing any decoding.
+       
+       :arg stream: the source of the bytes
+       :type stream: a file-like object
+       :arg max_width: the maximum length, in bytes, of the vint (defaults to :data:`EBMLMaxSizeLength`)
+       :type max_width: int
+       :returns: bytearray
+       
+       """
+       
+       marker_found = False
+       vint_bytes = bytearray()
+       vint_len = -7
+       while not marker_found:
+               vint_len += 8
+               if vint_len > max_width:
+                       raise ParseError('vint exceeds max_width (%(max_width)i)' % {
+                               'max_width': max_width
+                       })
+               byte = ord(stream.read(1))
+               vint_bytes.append(byte)
+               for pos in range(0, 8):
+                       mask = 0b10000000 >> pos
+                       if byte & mask:
+                               vint_len += pos
+                               marker_found = True
+                               break
+       
+       remaining_bytes_len = vint_len - len(vint_bytes)
+       if remaining_bytes_len > 0:
+               vint_bytes.extend(ord(remaining_byte) for remaining_byte in stream.read(remaining_bytes_len))
+       
+       if len(vint_bytes) != vint_len:
+               raise ParseError('Unable to read truncated vint of width %(vint_len)s from stream (%(vint_bytes)s bytes available)' % {
+                       'vint_len': vint_len,
+                       'vint_bytes': len(vint_bytes)
+               })
+       
+       return vint_bytes
+
+
+def read_element_size(stream, max_width=EBMLMaxSizeLength):
+       """
+       
+       Reads an EBML element size vint from stream and returns a tuple containing:
+       
+               * the size as an integer, or None if the size is undefined
+               * the length in bytes of the size descriptor (the vint) itself
+       
+       :arg stream: the source of the bytes
+       :type stream: a file-like object
+       :arg max_width: the maximum length, in bytes, of the vint storing the element size (defaults to :data:`EBMLMaxSizeLength`)
+       :type max_width: int
+       :returns: tuple
+       
+       """
+       
+       vint_bytes = _read_vint_to_bytearray(stream, max_width)
+       vint_len = len(vint_bytes)
+       
+       int_bytes = vint_bytes[((vint_len - 1) // 8):]
+       first_byte_mask = 0b10000000 >> ((vint_len - 1) % 8)
+       max_bytes = 0
+       
+       value = int_bytes[0] & (first_byte_mask - 1)
+       
+       if value == (first_byte_mask - 1):
+               max_bytes += 1
+       
+       for int_byte in int_bytes[1:]:
+               if int_byte == 0b11111111:
+                       max_bytes += 1
+               value = (value << 8) | int_byte
+       
+       if max_bytes == len(int_bytes):
+               value = None
+       
+       return value, vint_len
+
+
+def read_element_id(stream, max_width=EBMLMaxIDLength):
+       """
+       
+       Reads an EBML element ID vint from stream and returns a tuple containing:
+       
+               * the ID as an integer
+               * the length in bytes of the ID descriptor (the vint) itself
+       
+       :arg stream: the source of the bytes
+       :type stream: a file-like object
+       :arg max_width: the maximum length, in bytes, of the vint storing the element ID (defaults to :data:`EBMLMaxIDLength`)
+       :type max_width: int
+       :returns: tuple
+       
+       """
+       
+       vint_bytes = _read_vint_to_bytearray(stream, max_width)
+       vint_len = len(vint_bytes)
+       
+       value = 0
+       max_bytes = 0
+       min_bytes = 0
+       
+       for vint_byte in vint_bytes:
+               if vint_byte == 0b11111111:
+                       max_bytes += 1
+               elif vint_byte == 0:
+                       min_bytes += 1
+               value = (value << 8) | vint_byte
+       
+       if max_bytes == vint_len:
+               raise ReservedElementIDError('All value bits set to 1')
+       elif min_bytes == vint_len:
+               raise ReservedElementIDError('All value bits set to 0')
+       
+       return value, vint_len
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diff --git a/ebml/exceptions.py b/ebml/exceptions.py
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+++ b/ebml/exceptions.py
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+class EBMLException(Exception):
+       pass
+
+class ParseError(EBMLException):
+       pass
+
+class ReservedElementIDError(EBMLException):
+       pass
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