1# CRC32C 2 3[](https://travis-ci.org/google/crc32c) 4[](https://ci.appveyor.com/project/pwnall/crc32c) 5 6New file format authors should consider 7[HighwayHash](https://github.com/google/highwayhash). The initial version of 8this code was extracted from [LevelDB](https://github.com/google/leveldb), which 9is a stable key-value store that is widely used at Google. 10 11This project collects a few CRC32C implementations under an umbrella that 12dispatches to a suitable implementation based on the host computer's hardware 13capabilities. 14 15CRC32C is specified as the CRC that uses the iSCSI polynomial in 16[RFC 3720](https://tools.ietf.org/html/rfc3720#section-12.1). The polynomial was 17introduced by G. Castagnoli, S. Braeuer and M. Herrmann. CRC32C is used in 18software such as Btrfs, ext4, Ceph and leveldb. 19 20 21## Usage 22 23```cpp 24#include "crc32c/crc32c.h" 25 26int main() { 27 const std::uint8_t buffer[] = {0, 0, 0, 0}; 28 std::uint32_t result; 29 30 // Process a raw buffer. 31 result = crc32c::Crc32c(buffer, 4); 32 33 // Process a std::string. 34 std::string string; 35 string.resize(4); 36 result = crc32c::Crc32c(string); 37 38 // If you have C++17 support, process a std::string_view. 39 std::string_view string_view(string); 40 result = crc32c::Crc32c(string_view); 41 42 return 0; 43} 44``` 45 46 47## Prerequisites 48 49This project uses [CMake](https://cmake.org/) for building and testing. CMake is 50available in all popular Linux distributions, as well as in 51[Homebrew](https://brew.sh/). 52 53This project uses submodules for dependency management. 54 55```bash 56git submodule update --init --recursive 57``` 58 59If you're using [Atom](https://atom.io/), the following packages can help. 60 61```bash 62apm install autocomplete-clang build build-cmake clang-format language-cmake \ 63 linter linter-clang 64``` 65 66If you don't mind more setup in return for more speed, replace 67`autocomplete-clang` and `linter-clang` with `you-complete-me`. This requires 68[setting up ycmd](https://github.com/ycm-core/ycmd#building). 69 70```bash 71apm install autocomplete-plus build build-cmake clang-format language-cmake \ 72 linter you-complete-me 73``` 74 75## Building 76 77The following commands build and install the project. 78 79```bash 80mkdir build 81cd build 82cmake -DCRC32C_BUILD_TESTS=0 -DCRC32C_BUILD_BENCHMARKS=0 .. && make all install 83``` 84 85 86## Development 87 88The following command (when executed from `build/`) (re)builds the project and 89runs the tests. 90 91```bash 92cmake .. && cmake --build . && ctest --output-on-failure 93``` 94 95 96### Android testing 97 98The following command builds the project against the Android NDK, which is 99useful for benchmarking against ARM processors. 100 101```bash 102cmake .. -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \ 103 -DCMAKE_ANDROID_NDK=$HOME/Library/Android/sdk/ndk-bundle \ 104 -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \ 105 -DCMAKE_ANDROID_STL_TYPE=c++_static -DCRC32C_USE_GLOG=0 \ 106 -DCMAKE_BUILD_TYPE=Release && cmake --build . 107``` 108 109The following commands install and run the benchmarks. 110 111```bash 112adb push crc32c_bench /data/local/tmp 113adb shell chmod +x /data/local/tmp/crc32c_bench 114adb shell 'cd /data/local/tmp && ./crc32c_bench' 115adb shell rm /data/local/tmp/crc32c_bench 116``` 117 118The following commands install and run the tests. 119 120```bash 121adb push crc32c_tests /data/local/tmp 122adb shell chmod +x /data/local/tmp/crc32c_tests 123adb shell 'cd /data/local/tmp && ./crc32c_tests' 124adb shell rm /data/local/tmp/crc32c_tests 125``` 126
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