Inside Bitcoin

1# CRC32C
2
3[![Build Status](https://github.com/google/crc32c/actions/workflows/build.yml/badge.svg)](https://github.com/google/crc32c/actions/workflows/build.yml)
4
5New file format authors should consider
6[HighwayHash](https://github.com/google/highwayhash). The initial version of
7this code was extracted from [LevelDB](https://github.com/google/leveldb), which
8is a stable key-value store that is widely used at Google.
9
10This project collects a few CRC32C implementations under an umbrella that
11dispatches to a suitable implementation based on the host computer's hardware
12capabilities.
13
14CRC32C is specified as the CRC that uses the iSCSI polynomial in
15[RFC 3720](https://tools.ietf.org/html/rfc3720#section-12.1). The polynomial was
16introduced by G. Castagnoli, S. Braeuer and M. Herrmann. CRC32C is used in
17software such as Btrfs, ext4, Ceph and leveldb.
18
19
20## Usage
21
22```cpp
23#include "crc32c/crc32c.h"
24
25int main() {
26  const std::uint8_t buffer[] = {0, 0, 0, 0};
27  std::uint32_t result;
28
29  // Process a raw buffer.
30  result = crc32c::Crc32c(buffer, 4);
31
32  // Process a std::string.
33  std::string string;
34  string.resize(4);
35  result = crc32c::Crc32c(string);
36
37  // If you have C++17 support, process a std::string_view.
38  std::string_view string_view(string);
39  result = crc32c::Crc32c(string_view);
40
41  return 0;
42}
43```
44
45
46## Prerequisites
47
48This project uses [CMake](https://cmake.org/) for building and testing. CMake is
49available in all popular Linux distributions, as well as in
50[Homebrew](https://brew.sh/).
51
52This project uses submodules for dependency management.
53
54```bash
55git submodule update --init --recursive
56```
57
58If you're using [Atom](https://atom.io/), the following packages can help.
59
60```bash
61apm install autocomplete-clang build build-cmake clang-format language-cmake \
62    linter linter-clang
63```
64
65If you don't mind more setup in return for more speed, replace
66`autocomplete-clang` and `linter-clang` with `you-complete-me`. This requires
67[setting up ycmd](https://github.com/ycm-core/ycmd#building).
68
69```bash
70apm install autocomplete-plus build build-cmake clang-format language-cmake \
71    linter you-complete-me
72```
73
74## Building
75
76The following commands build and install the project.
77
78```bash
79mkdir build
80cd build
81cmake -DCRC32C_BUILD_TESTS=0 -DCRC32C_BUILD_BENCHMARKS=0 .. && make all install
82```
83
84
85## Development
86
87The following command (when executed from `build/`) (re)builds the project and
88runs the tests.
89
90```bash
91cmake .. && cmake --build . && ctest --output-on-failure
92```
93
94
95### Android testing
96
97The following command builds the project against the Android NDK, which is
98useful for benchmarking against ARM processors.
99
100```bash
101cmake .. -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
102    -DCMAKE_ANDROID_NDK=$HOME/Library/Android/sdk/ndk-bundle \
103    -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \
104    -DCMAKE_ANDROID_STL_TYPE=c++_static -DCRC32C_USE_GLOG=0 \
105    -DCMAKE_BUILD_TYPE=Release && cmake --build .
106```
107
108The following commands install and run the benchmarks.
109
110```bash
111adb push crc32c_bench /data/local/tmp
112adb shell chmod +x /data/local/tmp/crc32c_bench
113adb shell 'cd /data/local/tmp && ./crc32c_bench'
114adb shell rm /data/local/tmp/crc32c_bench
115```
116
117The following commands install and run the tests.
118
119```bash
120adb push crc32c_tests /data/local/tmp
121adb shell chmod +x /data/local/tmp/crc32c_tests
122adb shell 'cd /data/local/tmp && ./crc32c_tests'
123adb shell rm /data/local/tmp/crc32c_tests
124```
125