# 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/ycm-core/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
```
