1#
2# Copyright (C) 2018 The Android Open Source Project
3#
4# Licensed under the Apache License, Version 2.0 (the "License");
5# you may not use this file except in compliance with the License.
6# You may obtain a copy of the License at
7#
8#      http://www.apache.org/licenses/LICENSE-2.0
9#
10# Unless required by applicable law or agreed to in writing, software
11# distributed under the License is distributed on an "AS IS" BASIS,
12# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13# See the License for the specific language governing permissions and
14# limitations under the License.
15#
16"""This file contains ELF utility functions."""
17
18
19def DecodeSLEB128(data, begin_offset=0):
20    """Decode one int64 from SLEB128 encoded bytes.
21
22    Args:
23        data: A str, bytes to decode.
24        begin_offset: An integer, offset in data to start decode from.
25
26    Returns:
27        A tuple (value, num), the decoded value and number of consumed bytes.
28
29    Raises:
30        IndexError: String index out of range.
31    """
32    cur = begin_offset
33    value = 0
34    shift = 0
35    while True:
36        try:
37            byte, cur = ord(data[cur]), cur + 1
38        except IndexError:
39            raise
40        value |= (byte & 0x7F) << shift
41        shift += 7
42        if byte & 0x80 == 0:
43            break
44    if byte & 0x40:
45        value |= (-1) << shift
46    return value, cur - begin_offset
47