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#!/usr/bin/env python3
"""a leb128 decoder,encoder"""
import argparse
def devibytes(val):
"""A custom arg handler, just to handle bytes in hex format"""
ret = []
for byte in val.split(","):
ret.append(int(byte, 16))
return bytes(ret)
def LEB128UnsignedDecode(bytelist):
"""LEB128 unsiged decoder"""
result = 0
shift = 0
for byte in bytelist:
result |= (byte & 0x7F) << shift
if (byte & 0x80) == 0:
break
shift += 7
return result
def LEB128SignedDecode(bytelist):
"""LEB128 signed decoder"""
result = 0
shift = 0
for byte in bytelist:
result |= (byte & 0x7F) << shift
last_byte = byte
shift += 7
if (byte & 0x80) == 0:
break
if last_byte & 0x40:
result |= -(1 << shift)
return result
def LEB128UnsignedEncode(int_val):
"""LEB128 signed encoder"""
if int_val < 0:
raise Exception("value must not be negative")
if int_val == 0:
return bytes([0])
byte_array = bytearray()
while int_val:
byte = int_val & 0x7F
byte_array.append(byte | 0x80)
int_val >>= 7
byte_array[-1] ^= 0x80
return byte_array
def LEB128SignedEncode(int_val):
"""LEB128 signed encoder"""
byte_array = bytearray()
while True:
byte = int_val & 0x7F
byte_array.append(byte | 0x80)
int_val >>= 7
if (int_val == 0 and byte & 0x40 == 0) or (
int_val == -1 and byte & 0x40
):
byte_array[-1] ^= 0x80
break
return byte_array
# pylint: disable=too-few-public-methods
class Argparser:
"""CLI args"""
def __init__(self):
parser = argparse.ArgumentParser()
parser.add_argument("--se", type=int, help="leb128 signed encode")
parser.add_argument("--ue", type=int, help="leb128 unsigned encode")
parser.add_argument(
"--sd",
type=devibytes,
help="leb128 signed decode. pass a string like ef1289.",
)
parser.add_argument(
"--ud",
type=devibytes,
help="leb128 unsigned decode. pass a string like ef1290",
)
self.args = parser.parse_args()
def main():
"""entrypoint"""
argparser = Argparser()
# here
if argparser.args.se:
res = LEB128SignedEncode(argparser.args.se)
for byte in res:
print(format(byte, "02x"), end=" ")
print()
if argparser.args.ue:
res = LEB128UnsignedEncode(argparser.args.ue)
for byte in res:
print(format(byte, "02x"), end=" ")
print()
if argparser.args.sd:
print(LEB128SignedDecode(argparser.args.sd))
if argparser.args.ud:
print(LEB128UnsignedDecode(argparser.args.ud))
if __name__ == "__main__":
main()
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