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"""Varint encoder/decoder | |
varints are a common encoding for variable length integer data, used in | |
libraries such as sqlite, protobuf, v8, and more. | |
Here's a quick and dirty module to help avoid reimplementing the same thing | |
over and over again. | |
""" | |
# byte-oriented StringIO was moved to io.BytesIO in py3k | |
try: | |
from io import BytesIO | |
except ImportError: | |
from StringIO import StringIO as BytesIO | |
import sys | |
if sys.version > '3': | |
def _byte(b): | |
return bytes((b, )) | |
else: | |
def _byte(b): | |
return chr(b) | |
def encode(number): | |
"""Pack `number` into varint bytes""" | |
buf = b'' | |
while True: | |
towrite = number & 0x7f | |
number >>= 7 | |
if number: | |
buf += _byte(towrite | 0x80) | |
else: | |
buf += _byte(towrite) | |
break | |
return buf | |
def decode_stream(stream): | |
"""Read a varint from `stream`""" | |
shift = 0 | |
result = 0 | |
while True: | |
i = _read_one(stream) | |
result |= (i & 0x7f) << shift | |
shift += 7 | |
if not (i & 0x80): | |
break | |
return result | |
def decode_bytes(buf): | |
"""Read a varint from from `buf` bytes""" | |
return decode_stream(BytesIO(buf)) | |
def _read_one(stream): | |
"""Read a byte from the file (as an integer) | |
raises EOFError if the stream ends while reading bytes. | |
""" | |
c = stream.read(1) | |
if c == b'': | |
raise EOFError("Unexpected EOF while reading bytes") | |
return ord(c) |