1 | /* |
2 | * Copyright 2017-present Facebook, Inc. |
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 | |
17 | #pragma once |
18 | |
19 | #include <type_traits> |
20 | |
21 | #include <folly/io/Cursor.h> |
22 | #include <folly/io/IOBuf.h> |
23 | #include <folly/lang/Bits.h> |
24 | |
25 | /** |
26 | * Helper functions for compression codecs. |
27 | */ |
28 | namespace folly { |
29 | namespace io { |
30 | namespace compression { |
31 | namespace detail { |
32 | |
33 | /** |
34 | * Reads sizeof(T) bytes, and returns false if not enough bytes are available. |
35 | * Returns true if the first n bytes are equal to prefix when interpreted as |
36 | * a little endian T. |
37 | */ |
38 | template <typename T> |
39 | typename std::enable_if<std::is_unsigned<T>::value, bool>::type |
40 | dataStartsWithLE(const IOBuf* data, T prefix, uint64_t n = sizeof(T)) { |
41 | DCHECK_GT(n, 0); |
42 | DCHECK_LE(n, sizeof(T)); |
43 | T value; |
44 | Cursor cursor{data}; |
45 | if (!cursor.tryReadLE(value)) { |
46 | return false; |
47 | } |
48 | const T mask = n == sizeof(T) ? T(-1) : (T(1) << (8 * n)) - 1; |
49 | return prefix == (value & mask); |
50 | } |
51 | |
52 | template <typename T> |
53 | typename std::enable_if<std::is_arithmetic<T>::value, std::string>::type |
54 | prefixToStringLE(T prefix, uint64_t n = sizeof(T)) { |
55 | DCHECK_GT(n, 0); |
56 | DCHECK_LE(n, sizeof(T)); |
57 | prefix = Endian::little(prefix); |
58 | std::string result; |
59 | result.resize(n); |
60 | memcpy(&result[0], &prefix, n); |
61 | return result; |
62 | } |
63 | |
64 | } // namespace detail |
65 | } // namespace compression |
66 | } // namespace io |
67 | } // namespace folly |
68 | |