crc32c:CRC32C实现，支持特定于CPU的加速指令

# CRC32C [](https://travis-ci.org/google/crc32c) [](https://ci.appveyor.com/project/pwnall/crc32c) New file format authors should consider [HighwayHash](https://github.com/google/highwayhash). The initial version of this code was extracted from [LevelDB](https://github.com/google/leveldb), which is a stable key-value store that is widely used at Google. This project collects a few CRC32C implementations under an umbrella that dispatches to a suitable implementation based on the host computer's hardware capabilities. CRC32C is specified as the CRC that uses the iSCSI polynomial in [RFC 3720](https://tools.ietf.org/html/rfc3720#section-12.1). The polynomial was introduced by G. Castagnoli, S. Braeuer and M. Herrmann. CRC32C is used in software such as Btrfs, ext4, Ceph and leveldb. ## Usage ```cpp #include "crc32c/crc32c.h" int main() { const std::uint8_t buffer[] = {0, 0, 0, 0}; std::uint32_t result; // Process a raw buffer. result = crc32c::Crc32c(buffer, 4); // Process a std::string. std::string string; string.resize(4); result = crc32c::Crc32c(string); // If you have C++17 support, process a std::string_view. std::string_view string_view(string); result = crc32c::Crc32c(string_view); return 0; } ``` ## Prerequisites This project uses [CMake](https://cmake.org/) for building and testing. CMake is available in all popular Linux distributions, as well as in [Homebrew](https://brew.sh/). This project uses submodules for dependency management. ```bash git submodule update --init --recursive ``` If you're using [Atom](https://atom.io/), the following packages can help. ```bash apm install autocomplete-clang build build-cmake clang-format language-cmake \ linter linter-clang ``` If you don't mind more setup in return for more speed, replace `autocomplete-clang` and `linter-clang` with `you-complete-me`. This requires [setting up ycmd](https://github.com/Valloric/ycmd#building). ```bash apm install autocomplete-plus build build-cmake clang-format language-cmake \ linter you-complete-me ``` ## Building The following commands build and install the project. ```bash mkdir build cd build cmake -DCRC32C_BUILD_TESTS=0 -DCRC32C_BUILD_BENCHMARKS=0 .. && make all install ``` ## Development The following command (when executed from `build/`) (re)builds the project and runs the tests. ```bash cmake .. && cmake --build . && ctest --output-on-failure ``` ### Android testing The following command builds the project against the Android NDK, which is useful for benchmarking against ARM processors. ```bash cmake .. -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \ -DCMAKE_ANDROID_NDK=$HOME/Library/Android/sdk/ndk-bundle \ -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang \ -DCMAKE_ANDROID_STL_TYPE=c++_static -DCRC32C_USE_GLOG=0 \ -DCMAKE_BUILD_TYPE=Release && cmake --build . ``` The following commands install and run the benchmarks. ```bash adb push crc32c_bench /data/local/tmp adb shell chmod +x /data/local/tmp/crc32c_bench adb shell 'cd /data/local/tmp && ./crc32c_bench' adb shell rm /data/local/tmp/crc32c_bench ``` The following commands install and run the tests. ```bash adb push crc32c_tests /data/local/tmp adb shell chmod +x /data/local/tmp/crc32c_tests adb shell 'cd /data/local/tmp && ./crc32c_tests' adb shell rm /data/local/tmp/crc32c_tests ```